Journal articles: 'Polar cusps'

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Tsyganenko, N. A. "Magnetic field and electric currents in the vicinity of polar cusps as inferred from Polar and Cluster data." Annales Geophysicae 27, no. 4 (April 2, 2009): 1573–82. http://dx.doi.org/10.5194/angeo-27-1573-2009.

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Abstract. A detailed statistical study of the magnetic structure of the dayside polar cusps is presented, based on multi-year sets of magnetometer data of Polar and Cluster spacecraft, taken in 1996–2006 and 2001–2007, respectively. Thanks to the dense data coverage in both Northern and Southern Hemispheres, the analysis spanned nearly the entire length of the cusps, from low altitudes to the cusp "throat" and the magnetosheath. Subsets of data falling inside the polar cusp "funnels" were selected with the help of TS05 and IGRF magnetic field models, taking into account the dipole tilt and the solar wind/IMF conditions. The selection funnels were shifted within ±10° of SM latitude around the model cusp location, and linear regression parameters were calculated for each sliding subset, further divided into 10 bins of distance in the range 2≤R≤12 RE, with the following results. (1) Diamagnetic depression, caused by the penetrated magnetosheath plasma, becomes first visible at R~4–5 RE, rapidly deepens with growing R, peaks at R~6–9 RE, and then partially subsides and widens in latitude at the cusp's outer end. (2) The depression peak is systematically shifted poleward (by ~2° of the footpoint latitude) with respect to the model cusp field line, passing through the min{|B|} point at the magnetopause. (3) At all radial distances, clear and distinct peaks of the correlation between the local By and By(IMF) and of the corresponding proportionality coefficient are observed. A remarkably regular variation of that coefficient with R quantitatively confirms the field-aligned geometry of the cusp currents associated with the IMF By, found in earlier observations.

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Błęcki, Jan, Roman Wronowski, Jan Słomiński, Sergey Savin, Rafał Iwański, and Roger Haagmans. "Comparative Study of the Energetic Electrons Registered Together with the Broad Band Emissions in Different Regions of the Ionosphere." Artificial Satellites 55, no. 4 (December 1, 2020): 130–49. http://dx.doi.org/10.2478/arsa-2020-0010.

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Abstract ELF/VLF waves have been registered in the outer polar cusps simultaneously with high energy electrons fluxes by the satellites Magion 4 (subsatellite to Interball 1), Polar and CLUSTER. Further, we discuss similar observations in the different regions of the ionosphere, where DEMETER registered energetic electrons. The DEMETER satellite operating on the nearly polar orbit at the altitude 650 km crossed different regions in the ionosphere. Registrations of ELF/VLF/HF waves together with the energetic electrons in the polar cusp, in the ionospheric trough and over thunderstorm areas are presented in this paper. The three satellites of ESA’s Swarm mission provide additional information on the ELF waves in the mentioned areas together with electron density and temperature. A brief discussion of the generation of these emissions by the so-called “fan instability” (FI) and beam instability is presented.

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Chen, S. H., S. A. Boardsen, S. F. Fung, J. L. Green, R. L. Kessel, L. C. Tan, T. E. Eastman, and J. D. Craven. "Exterior and interior polar cusps: Observations from Hawkeye." Journal of Geophysical Research: Space Physics 102, A6 (June 1, 1997): 11335–47. http://dx.doi.org/10.1029/97ja00743.

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Candidi, M., and C. I. Meng. "Low-altitude observations of the conjugate polar cusps." Journal of Geophysical Research 93, A2 (1988): 923. http://dx.doi.org/10.1029/ja093ia02p00923.

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Tsyganenko, N. A., and C. T. Russell. "Magnetic signatures of the distant polar cusps: Observations by Polar and quantitative modeling." Journal of Geophysical Research: Space Physics 104, A11 (November 1, 1999): 24939–55. http://dx.doi.org/10.1029/1999ja900279.

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Lin, N., E. S. Lee, J. McFadden, G. Parks, M. Wilber, M. Maksimovic, N. Cornilleau-Wehrlin, et al. "VLF/ELF wave activity in the vicinity of the polar cusp: Cluster observations." Annales Geophysicae 24, no. 7 (August 9, 2006): 1993–2004. http://dx.doi.org/10.5194/angeo-24-1993-2006.

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Abstract. Observations by the Cluster spacecraft of VLF/ELF wave activity show distinct signatures for different regions in the vicinity of high altitude polar cusps, which are identified by using magnetic field and plasma data along spacecraft trajectories. These waves include: (1) Broad band magnetic noise observed in the polar cusp at frequencies from several Hz to ~100 Hz, below the local electron cyclotron frequency, fce. Similar magnetic noise is also observed in the high latitude magnetosheath and the magnetopause boundary layer. (2) Strong broad band electrostatic emissions observed in the cusp, in the magnetosheath, and in the high latitude magnetopause boundary layer, at frequencies extending from several Hz to tens of kHz, with maximum intensities below ~100 Hz. (3) Narrow-band electromagnetic whistler waves at frequencies ~0.2–0.6 fce, frequently observed in the closed boundary layer (CBL) adjacent to the polar cusp. These waves are for the first time observed in this region to be accompanied by counter-streaming electron beams of ~100 eV, which suggests that the waves are excited by these electrons through wave-particle interaction. (4) Narrow-band electrostatic waves observed slightly above the local fce in the CBL. (5) Lion roars, observed in the high latitude magnetosheath, often in magnetic troughs of mirror mode oscillations. The above wave signatures can serve as indicators of the regions in the vicinity of the magnetospheric cusp.

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Savin, S., J. Büchner, G. Consolini, B. Nikutowski, L. Zelenyi, E. Amata, H. U. Auster, et al. "On the properties of turbulent boundary layer over polar cusps." Nonlinear Processes in Geophysics 9, no. 5/6 (December 31, 2002): 443–51. http://dx.doi.org/10.5194/npg-9-443-2002.

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Abstract. We study properties of nonlinear magnetic fluctuations in the turbulent boundary layer (TBL) over polar cusps during a typical TBL crossing on 19 June 1998. Interball-1data in the summer TBL are compared with that of Geotail in solar wind (SW) and Polar in the northern TBL. In the TBL two characteristic slopes are seen: ~ - 1 at (0.004- 0.08) Hz and ~ - 2.2 at (0.08-2) Hz. We present evidences that random current sheets with features of coherent solitons can result in: (i) slopes of ~ - 1 in the magnetic power spectra; (ii) demagnetization of the SW plasma in "diamagnetic bubbles"; (iii) nonlinear, presumably, 3-wave phase coupling with cascade features; (iiii) departure from the Gaussian statistics. We discuss the above TBL properties in terms of intermittency and self-organization of nonlinear systems, and compare them with kinetic simulations of reconnected current sheet at the nonlinear state. Virtual satellite data in the model current sheet reproduce valuable cascade-like spectral and bi-spectral properties of the TBL turbulence.

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Tsyganenko, N. A., and V. A. Andreeva. "Empirical Modeling of Dayside Magnetic Structures Associated With Polar Cusps." Journal of Geophysical Research: Space Physics 123, no. 11 (November 2018): 9078–92. http://dx.doi.org/10.1029/2018ja025881.

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Voigt, G. H., and R. A. Wolf. "On the configuration of the polar cusps in Earth's magnetosphere." Journal of Geophysical Research 90, A5 (1985): 4046. http://dx.doi.org/10.1029/ja090ia05p04046.

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Yordanova, E., J. Bergman, G. Consolini, M. Kretzschmar, M. Materassi, B. Popielawska, M. Roca-Sogorb, K. Stasiewicz, and A. W. Wernik. "Anisotropic scaling features and complexity in magnetospheric-cusp: a case study." Nonlinear Processes in Geophysics 12, no. 6 (September 14, 2005): 817–25. http://dx.doi.org/10.5194/npg-12-817-2005.

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Abstract. Magnetospheric cusps are high-latitude regions characterized by a highly turbulent plasma, playing a special role in the solar wind-magnetosphere interaction. Here, using POLAR satellite magnetic field vector measurements we investigate the anisotropic scaling features of the magnetic field fluctuations in the northern cusp region. Our results seem to support the hypothesis of a 2D-MHD turbulent scenario which is consequence of a strong background magnetic field. The observed turbulent fluctuations reveal a high degree of complexity, which might be due to the interplay of many competing scales. A discussion of our findings in connection with the complex scenario proposed by Chang et al. (2004) is provided.

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11

Prikryl, P., L. Spogli, P. T. Jayachandran, J. Kinrade, C. N. Mitchell, B. Ning, G. Li, et al. "Interhemispheric comparison of GPS phase scintillation at high latitudes during the magnetic-cloud-induced geomagnetic storm of 5–7 April 2010." Annales Geophysicae 29, no. 12 (December 21, 2011): 2287–304. http://dx.doi.org/10.5194/angeo-29-2287-2011.

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Abstract. Arrays of GPS Ionospheric Scintillation and TEC Monitors (GISTMs) are used in a comparative scintillation study focusing on quasi-conjugate pairs of GPS receivers in the Arctic and Antarctic. Intense GPS phase scintillation and rapid variations in ionospheric total electron content (TEC) that can result in cycle slips were observed at high latitudes with dual-frequency GPS receivers during the first significant geomagnetic storm of solar cycle 24 on 5–7 April 2010. The impact of a bipolar magnetic cloud of north-south (NS) type embedded in high speed solar wind from a coronal hole caused a geomagnetic storm with maximum 3-hourly Kp = 8- and hourly ring current Dst = −73 nT. The interhemispheric comparison of phase scintillation reveals similarities but also asymmetries of the ionospheric response in the northern and southern auroral zones, cusps and polar caps. In the nightside auroral oval and in the cusp/cleft sectors the phase scintillation was observed in both hemispheres at about the same times and was correlated with geomagnetic activity. The scintillation level was very similar in approximately conjugate locations in Qiqiktarjuaq (75.4° N; 23.4° E CGM lat. and lon.) and South Pole (74.1° S; 18.9° E), in Longyearbyen (75.3° N; 111.2° E) and Zhongshan (74.7° S; 96.7° E), while it was significantly higher in Cambridge Bay (77.0° N; 310.1° E) than at Mario Zucchelli (80.0° S; 307.7° E). In the polar cap, when the interplanetary magnetic field (IMF) was strongly northward, the ionization due to energetic particle precipitation was a likely cause of scintillation that was stronger at Concordia (88.8° S; 54.4° E) in the dark ionosphere than in the sunlit ionosphere over Eureka (88.1° N; 333.4° E), due to a difference in ionospheric conductivity. When the IMF tilted southward, weak or no significant scintillation was detected in the northern polar cap, while in the southern polar cap rapidly varying TEC and strong phase scintillation persisted for many hours. This interhemispheric asymmetry is explained by the difference in the location of solar terminator relative to the cusps in the Northern and Southern Hemisphere. Solar terminator was in the immediate proximity of the cusp in the Southern Hemisphere where sunlit ionospheric plasma was readily convected into the central polar cap and a long series of patches was observed. In contrast, solar terminator was far poleward of the northern cusp thus reducing the entry of sunlit plasma and formation of dense patches. This is consistent with the observed and modeled seasonal variation in occurrence of polar cap patches. The GPS scintillation and TEC data analysis is supported by data from ground-based networks of magnetometers, riometers, ionosondes, HF radars and all-sky imagers, as well as particle flux measurements by DMSP satellites.

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12

Edge, W. L. "A plane sextic and its five cusps." Proceedings of the Royal Society of Edinburgh: Section A Mathematics 118, no. 3-4 (1991): 209–23. http://dx.doi.org/10.1017/s030821050002905x.

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SynopsisA certain plane sextic of genus 5 was encountered by Humbert and publicised by him [3] in 1894. Its striking geometrical properties clamour for elucidation; this was eventually supplied in 1951. For the canonical curve of genus 5 is the base curve C of a net N of quadrics in projective space [4], and C models a Humbert curve when all the quadrics of N have a common self-polar simplex [1]. The projection of C from one of its chords onto a plane is a 5-nodal sextic, the nodes all becoming cusps when the chord of C becomes a tangent. The properties to be elucidated become clear visually in the projection.The sextic H described here is a specialisation of the cusped curve; it emerges as linearly dependent on a pair of reducible plane sextics concocted ad hoc.

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Grandin, Maxime, Lucile Turc, Markus Battarbee, Urs Ganse, Andreas Johlander, Yann Pfau-Kempf, Maxime Dubart, and Minna Palmroth. "Hybrid-Vlasov simulation of auroral proton precipitation in the cusps: Comparison of northward and southward interplanetary magnetic field driving." Journal of Space Weather and Space Climate 10 (2020): 51. http://dx.doi.org/10.1051/swsc/2020053.

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Particle precipitation is a central aspect of space weather, as it strongly couples the magnetosphere and the ionosphere and can be responsible for radio signal disruption at high latitudes. We present the first hybrid-Vlasov simulations of proton precipitation in the polar cusps. We use two runs from the Vlasiator model to compare cusp proton precipitation fluxes during southward and northward interplanetary magnetic field (IMF) driving. The simulations reproduce well-known features of cusp precipitation, such as a reverse dispersion of precipitating proton energies, with proton energies increasing with increasing geomagnetic latitude under northward IMF driving, and a nonreversed dispersion under southward IMF driving. The cusp is also found more polewards in the northward IMF simulation than in the southward IMF simulation. In addition, we find that the bursty precipitation during southward IMF driving is associated with the transit of flux transfer events in the vicinity of the cusp. In the northward IMF simulation, dual lobe reconnection takes place. As a consequence, in addition to the high-latitude precipitation spot associated with the lobe reconnection from the same hemisphere, we observe lower-latitude precipitating protons which originate from the opposite hemisphere’s lobe reconnection site. The proton velocity distribution functions along the newly closed dayside magnetic field lines exhibit multiple proton beams travelling parallel and antiparallel to the magnetic field direction, which is consistent with previously reported observations with the Cluster spacecraft. In both runs, clear electromagnetic ion cyclotron waves are generated in the cusps and might further increase the calculated precipitating fluxes by scattering protons to the loss cone in the low-altitude cusp. Global kinetic simulations can improve the understanding of space weather by providing a detailed physical description of the entire near-Earth space and its internal couplings.

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Yordanova, E., M. Grzesiak, A. W. Wernik, B. Popielawska, and K. Stasiewicz. "Multifractal structure of turbulence in the magnetospheric cusp." Annales Geophysicae 22, no. 7 (July 14, 2004): 2431–40. http://dx.doi.org/10.5194/angeo-22-2431-2004.

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Abstract. Magnetospheric cusps are regions which are characterized by highly turbulent plasma. We have used Polar magnetic field data to study the structure of turbulence in the cusp region. The wavelet transform modulus maxima method (WTMM) has been applied to estimate the scaling exponent of the partition function and singularity spectra. Their features are similar to those found in the nonlinear multifractal systems. We have found that the scaling exponent does not allow one to conclude which intermittency model fits the experiment better. However, the singularity spectra reveal that different models can be ascribed to turbulence observed under various IMF conditions. For northward IMF conditions the turbulence is consistent with the multifractal p-model of fully developed fluid turbulence. For southward IMF experimental data agree with the model of non-fully developed Kolmogorov-like fluid turbulence.

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Escoubet, C. P., J. Berchem, K. J. Trattner, F. Pitout, R. Richard, M. G. G. T. Taylor, J. Soucek, et al. "Double cusp encounter by Cluster: double cusp or motion of the cusp?" Annales Geophysicae 31, no. 4 (April 19, 2013): 713–23. http://dx.doi.org/10.5194/angeo-31-713-2013.

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Abstract. Modelling plasma entry in the polar cusp has been successful in reproducing ion dispersions observed in the cusp at low and mid-altitudes. The use of a realistic convection pattern, when the IMF-By is large and stable, allowed Wing et al. (2001) to predict double cusp signatures that were subsequently observed by the DMSP spacecraft. In this paper we present a cusp crossing where two cusp populations are observed, separated by a gap around 1° Invariant Latitude (ILAT) wide. Cluster 1 (C1) and Cluster 2 (C2) observed these two cusp populations with a time delay of 3 min, and about 15 and 42 min later Cluster 4 (C4) and Cluster 3 (C3) observed, respectively, a single cusp population. A peculiarity of this event is the fact that the second cusp population seen on C1 and C2 was observed at the same time as the first cusp population on C4. This would tend to suggest that the two cusp populations had spatial features similar to the double cusp. Due to the nested crossing of C1 and C2 through the gap between the two cusp populations, C2 being first to leave the cusp and last to re-enter it, these observations are difficult to be explained by two distinct cusps with a gap in between. However, since we observe the cusp in a narrow area of local time post-noon, a second cusp may have been present in the pre-noon sector but could not be observed. On the other hand, these observations are in agreement with a motion of the cusp first dawnward and then back duskward due to the effect of the IMF-By component.

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Гульельми, Анатолий, Anatol Guglielmi, Борис Клайн, Boris Klain, Александр Потапов, and Alexander Potapov. "North-south asymmetry of ultra-low-frequency oscillations of Earth’s electromagnetic field." Solar-Terrestrial Physics 3, no. 4 (December 29, 2017): 26–31. http://dx.doi.org/10.12737/stp-34201703.

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In the paper, we present the result of an experimental study of north-south asymmetry of ultralow-frequency electromagnetic oscillations IPCL. This study is based on observations made at Mirny Observatory (Antarctica). IPCLs are excited in the dayside sector of the auroral oval in the range 3–10 min periods and represent one of the most powerful types of oscillations of Earth's magnetosphere. These oscillations were discovered in the 1970s during IPhE AS USSR polar expeditions organized by Prof. V.A. Troitskaya. We have shown that IPCL activity in Mirny depends on the inclination (north-south asymmetry) of interplanetary magnetic field (IMF) lines to the plane of the geomagnetic equator before the front of the magnetosphere. The result suggests a controlling exposure of IMF on the magnetospheric oscillations and gives rise to the hypothesis that IPCL are forced oscillations of a nonlinear dynamical system whose major structural elements are dayside polar cusps. The paper is dedicated to the memory of Professor V.A. Troitskaya (1917–2010).

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Гульельми, Анатолий, Anatol Guglielmi, Борис Клайн, Boris Klain, Александр Потапов, and Alexander Potapov. "North-south asymmetry of ultra-low-frequency oscillations of Earth’s electromagnetic field." Solnechno-Zemnaya Fizika 3, no. 4 (December 27, 2017): 27–33. http://dx.doi.org/10.12737/szf-34201703.

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In the paper, we present the result of an experimental study of north-south asymmetry of ultra-low-frequency electromagnetic oscillations IPCL. This study is based on observations made at obs. Mirny (Antarctica). IPCL are excited in the dayside sector of the auroral oval in the range of 3–10 min periods and represent one of the most powerful types of oscillations of Earth’s magnetosphere. These oscillations were discovered in the 1970s during IPhE AS USSR polar expeditions organized by Prof. V.A. Troitskaya. We have shown that IPCL activity in Mirny depends on the inclination (north-south asymmetry) of interplanetary magnetic field (IMF) lines to the plane of the geomagnetic equator before the front of the magnetosphere. The result suggests a controlling exposure of IMF on the magnetospheric oscillations and gives rise to the hypothesis that IPCL are forced oscillations of a nonlinear dynamical system whose major structural elements are dayside polar cusps. The paper is dedicated to the memory of Professor V.A. Troitskaya (1917–2010).

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Yoon, Duk Yong, Young Kyu Cho, and Hyun Min Jang. "Grain Boundary Roughening Transition." Materials Science Forum 467-470 (October 2004): 825–34. http://dx.doi.org/10.4028/www.scientific.net/msf.467-470.825.

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Flat surfaces and grain boundaries lying on low crystal planes are singular corresponding to the cusps in the polar (Wulff) plots of their energy against their orientation. The theoretical analysis of the entropy effect at high temperatures shows that these interfaces undergo roughening transitions. The molecular dynamics simulations also show disordering to liquid-like structures at high temperatures that can be interpreted as the roughening transition. Experimentally, singular flat surfaces and grain boundaries become curved at high temperatures or with additives, indicating their roughening transition. The grain boundaries in polycrystals are often faceted with hill-and-valley shapes and their defaceting at high temperatures also show their roughening transition.

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Liebert, Evelyn, Christian Nabert, Christopher Perschke, Karl-Heinz Fornaçon, and Karl-Heinz Glassmeier. "Statistical survey of day-side magnetospheric current flow using Cluster observations: magnetopause." Annales Geophysicae 35, no. 3 (May 17, 2017): 645–57. http://dx.doi.org/10.5194/angeo-35-645-2017.

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Abstract. We present a statistical survey of current structures observed by the Cluster spacecraft at high-latitude day-side magnetopause encounters in the close vicinity of the polar cusps. Making use of the curlometer technique and the fluxgate magnetometer data, we calculate the 3-D current densities and investigate the magnetopause current direction, location, and magnitude during varying solar wind conditions. We find that the orientation of the day-side current structures is in accordance with existing magnetopause current models. Based on the ambient plasma properties, we distinguish five different transition regions at the magnetopause surface and observe distinctive current properties for each region. Additionally, we find that the location of currents varies with respect to the onset of the changes in the plasma environment during magnetopause crossings.

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Quillen, Alice C., Nadine Neumayer, Tom Oosterloo, and Daniel Espada. "The Warped Disk of Centaurus A from a Radius of 2 to 6500 pc." Publications of the Astronomical Society of Australia 27, no. 4 (2010): 396–401. http://dx.doi.org/10.1071/as09069.

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AbstractWe compile position and inclination angles for tilted ring fits to the warped dusty and gaseous disk of Cen A, spanning a radius of 1.8 to 6500 pc, from recent observations. For radii exterior to 1 kpc, tilted-ring orientations lie on an arc, on a plot of polar-inclination versus position-angle, suggesting that precession following a merger can account for the ring morphology. Three kinks in the ring orientations are seen on the polar plot, the one at radius of about 1.3 kpc we suspect corresponds to the location where self-gravity in the disk affects the ring precession rate. Another at a radius of about 600 pc may be associated with a gap in the gas distribution. A third kink is seen at a radius of 100 pc. A constant inclination tilted disk precessing about the jet axis may describe the disk between 100 and 20 pc but not interior to this. A model with disk orientation matching the molecular circumnuclear disk at 100 pc that decays at smaller radii to an inner flat disk perpendicular to the jet may account for disk orientations within 100 pc. Neither model would account for the cusps or changes in disk orientation at 100 or 600 pc.

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Wang, Mei-Qing, Min Zhang, and Jun-Hua Zhang. "Photoelastic Study of the Effects of Occlusal Surface Morphology on Tooth Apical Stress from Vertical Bite Forces." Journal of Contemporary Dental Practice 5, no. 1 (2004): 74–93. http://dx.doi.org/10.5005/jcdp-5-1-74.

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Abstract The aim of the study was to determine how the morphology of occlusal surfaces might affect occlusal loading that is transferred to the tooth apex. Photoelastic methods were used to assess apical stress generated by seven variations of occlusions. A test assembly with a 2 kg weight was applied to teeth to create a vertical load. By analyzing the direction and magnitude of the apical principle stress under the polar light that was measured at the apexes of mandibular teeth, the occlusal loading position of each tooth and its direction was obtained based on general mechanical principles. It was found distal incline planes (or slopes) of cusps and lingual incline planes (or slope) of buccal cusps of mandibular posterior teeth carried the greatest occlusal load in normal occlusion. In the other six variations of occlusion presented in this study, the principle apical stresses changed more or less as a result of the different occlusal contact relationships. The magnitude of principle apical stress increased considerably in the flat surface occlusion because of the lack of distribution of occlusion loading by the smooth dentition surface. It is concluded the occlusal surface morphology has a significant effect on the direction and magnitude of apical stress. To establish a suitable relationship of occlusion that can conduct favorable occlusal loading physiologically is very important. Citation Wang M, Zhang M, Zhang J. Photoelastic Study of the Effects of Occlusal Surface Morphology on Tooth Apical Stress from Vertical Bite Forces . J Contemp Dent Pract 2004 February;(5)1:074-093.

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Farrugia, C. J., A. Grocott, P. E. Sandholt, S. W. H. Cowley, Y. Miyoshi, F. J. Rich, V. K. Jordanova, R. B. Torbert, and A. Sharma. "The magnetosphere under weak solar wind forcing." Annales Geophysicae 25, no. 1 (February 1, 2007): 191–205. http://dx.doi.org/10.5194/angeo-25-191-2007.

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Abstract. The Earth's magnetosphere was very strongly disturbed during the passage of the strong shock and the following interacting ejecta on 21–25 October 2001. These disturbances included two intense storms (Dst*≈−250 and −180 nT, respectively). The cessation of this activity at the start of 24 October ushered in a peculiar state of the magnetosphere which lasted for about 28 h and which we discuss in this paper. The interplanetary field was dominated by the sunward component [B=(4.29±0.77, −0.30±0.71, 0.49±0.45) nT]. We analyze global indicators of geomagnetic disturbances, polar cap precipitation, ground magnetometer records, and ionospheric convection as obtained from SuperDARN radars. The state of the magnetosphere is characterized by the following features: (i) generally weak and patchy (in time) low-latitude dayside reconnection or reconnection poleward of the cusps; (ii) absence of substorms; (iii) a monotonic recovery from the previous storm activity (Dst corrected for magnetopause currents decreasing from ~−65 to ~−35 nT), giving an unforced decreased of ~1.1 nT/h; (iv) the probable absence of viscous-type interaction originating from the Kelvin-Helmholtz (KH) instability; (v) a cross-polar cap potential of just 20–30 kV; (vi) a persistent, polar cap region containing (vii) very weak, and sometimes absent, electron precipitation and no systematic inter-hemisphere asymmetry. Whereas we therefore infer the presence of a moderate amount of open flux, the convection is generally weak and patchy, which we ascribe to the lack of solar wind driver. This magnetospheric state approaches that predicted by Cowley and Lockwood (1992) but has never yet been observed.

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Maynard, N. C., W. J. Burke, J. D. Scudder, D. M. Ober, G. L. Siscoe, W. W. White, K. D. Siebert, et al. "Observed and simulated depletion layers with southward IMF." Annales Geophysicae 22, no. 6 (June 14, 2004): 2151–69. http://dx.doi.org/10.5194/angeo-22-2151-2004.

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Abstract. We present observations from the Polar satellite that confirm the existence of two types of depletion layers predicted under southward interplanetary magnetic field (IMF) conditions in magnetohydrodynamic simulations. The first depletion type occurs along the stagnation line when IMF BX and/or dipole tilt are/is present. Magnetic merging occurred away from the equator (Maynard et al., 2003) and flux pile-ups developed while the field lines drape to the high-latitude merging sites. This high-shear type of depletion is consistent with the depletion layer model suggested by Zwan and Wolf (1976) for low-shear northward IMF conditions. Expected sites for depletion layers are associated with places where IMF tubes of force first impinge upon the magnetopause. The second depletion type develops poleward of the cusp. Under strongly driven conditions, magnetic fields from Region 1 current closure over the lobes (Siscoe et al., 2002c) cause the high-latitude magnetopause to bulge outward, creating a shoulder above the cusp. These shoulders present the initial obstacle with which the IMF interacts. Flow is impeded, causing local flux pile-ups and low-shear depletion layers to form poleward of the cusps. Merging at the high-shear dayside magnetopause is consequently delayed. In both low- and high-shear cases, we show that the depletion layer structure is part of a slow mode wave standing in front of the magnetopause. As suggested by Southwood and Kivelson (1995), the depletions are rarefactions on the magnetopause side of slow-mode density compressions. While highly sheared magnetic fields are often used as proxies for ongoing local magnetic merging, depletion layers are prohibited at merging locations. Therefore, the existence of a depletion layer is evidence that the location of merging must be remote relative to the observation.

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Potapov, Alexander, Anatol Guglielmi, and Boris Dovbnya. "ULTRA LOW FREQUENCY EMISSIONS RANGING FROM 0.1 TO 3 Hz IN CIRCUMPOLAR AREAS." Solnechno-Zemnaya Fizika 6, no. 3 (September 22, 2020): 48–55. http://dx.doi.org/10.12737/szf-63202006.

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We examine the characteristics of oscillations of two types in the high-frequency edge of the ULF range (0.1–3 Hz), serpentine emission (SE), and discrete frequency dispersed signals (DS). Oscillations of both the types are observed in the polar caps exclusively with induction magnetometers. Since these instruments are currently practically absent at high latitudes, the analysis has been carried out from records obtained at the stations Vostok and Thule close to the geomagnetic poles in 1968–1971. The DS occurrence rate is shown to have a sharp peak at local magnetic noon. This fact indicates that DS emergence is rigidly tied to the geomagnetic field line passing through the observation station. At the same time, the seasonal variation in the frequency of DS occurrence has a main peak in local summer and an additional peak in local winter. We have revealed before that at least a part of DS is excited in the foreshock region. Taking this into account, we can assume that the wave packets incident to the magnetopause fall on the external field lines mainly in the noon region and propagate along these lines in both directions, eventually reaching Earth’s surface in the polar regions. Unlike DS, the SE occurrence rate has neither a daily nor a seasonal variation. We have tested and confirmed indirectly the hypothesis put forward earlier about the excitation of SE by cyclotron instability of protons in the solar wind, simulating frequency variations in ion-cyclotron waves at different levels of interplanetary plasma perturbation and comparing the results with the SE frequency variations observed under similar conditions. We conclude that it is necessary to resume continuous observations of ULF emissions, using induction magnetometers installed in polar caps near the projections of cusps and near geomagnetic poles.

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Potapov, Alexander, Anatol Guglielmi, and Boris Dovbnya. "ULTRA LOW FREQUENCY EMISSIONS RANGING FROM 0.1 TO 3 Hz IN CIRCUMPOLAR AREAS." Solar-Terrestrial Physics 6, no. 3 (September 22, 2020): 40–45. http://dx.doi.org/10.12737/stp-63202006.

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We examine the characteristics of oscillations of two types in the high-frequency edge of the ULF range (0.1–3 Hz), serpentine emission (SE), and discrete frequency dispersed signals (DS). Oscillations of both the types are observed in the polar caps exclusively with induction magnetometers. Since these instruments are currently practically absent at high latitudes, the analysis has been carried out from records obtained at the stations Vostok and Thule close to the geomagnetic poles in 1968–1971. The DS occurrence rate is shown to have a sharp peak at local magnetic noon. This fact indicates that DS emergence is rigidly tied to the geomagnetic field line passing through the observation station. At the same time, the seasonal variation in the frequency of DS occurrence has a main peak in local summer and an additional peak in local winter. We have revealed before that at least a part of DS is excited in the foreshock region. Taking this into account, we can assume that the wave packets incident to the magnetopause fall on the external field lines mainly in the noon region and propagate along these lines in both directions, eventually reaching Earth’s surface in the polar regions. Unlike DS, the SE occurrence rate has neither a daily nor a seasonal variation. We have tested and confirmed indirectly the hypothesis put forward earlier about the excitation of SE by cyclotron instability of protons in the solar wind, simulating frequency variations in ion-cyclotron waves at different levels of interplanetary plasma perturbation and comparing the results with the SE frequency variations observed under similar conditions. We conclude that it is necessary to resume continuous observations of ULF emissions, using induction magnetometers installed in polar caps near the projections of cusps and near geomagnetic poles.

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26

Gunell, Herbert, Romain Maggiolo, Hans Nilsson, Gabriella Stenberg Wieser, Rikard Slapak, Jesper Lindkvist, Maria Hamrin, and Johan De Keyser. "Why an intrinsic magnetic field does not protect a planet against atmospheric escape." Astronomy & Astrophysics 614 (June 2018): L3. http://dx.doi.org/10.1051/0004-6361/201832934.

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The presence or absence of a magnetic field determines the nature of how a planet interacts with the solar wind and what paths are available for atmospheric escape. Magnetospheres form both around magnetised planets, such as Earth, and unmagnetised planets, like Mars and Venus, but it has been suggested that magnetised planets are better protected against atmospheric loss. However, the observed mass escape rates from these three planets are similar (in the approximate (0.5–2) kg s−1 range), putting this latter hypothesis into question. Modelling the effects of a planetary magnetic field on the major atmospheric escape processes, we show that the escape rate can be higher for magnetised planets over a wide range of magnetisations due to escape of ions through the polar caps and cusps. Therefore, contrary to what has previously been believed, magnetisation is not a sufficient condition for protecting a planet from atmospheric loss. Estimates of the atmospheric escape rates from exoplanets must therefore address all escape processes and their dependence on the planet’s magnetisation.

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27

Ji, Wu, Bai Qingjiang, and Xu Yongjian. "International cooperation: A brief history We’ve experienced." Journal of Space Weather and Space Climate 11 (2021): 27. http://dx.doi.org/10.1051/swsc/2021008.

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The solar-terrestrial space is of considerable significance for human activities. Since the first artificial satellite Sputnik 1 was launched in 1957, more knowledge about the dynamic conditions of the space environment has been acquired. With growing dependence on modern technology – both in space and on the ground, the vulnerability of the modern society and its infrastructure to space weather has increased dramatically. To better understand, forecast and reduce the adverse effects of space weather, science programs on space weather always prioritize the measurement or acquisition of the data from different locations of the geo-space, such as in magnetopause, polar cusps, and the magnetic tail. For the ground observations, it is necessary to locate the instruments in different longitudes and latitudes. For a single country, it is impossible to cover all these observation points. Therefore, international cooperation is very much needed. The paper reviews some of the international space weather observation programs we have experienced at the system design level. It may provide lessons learned for the community that may enable such kind of cooperative programs in the future.

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Spjeldvik, W. N., T. A. Fritz, J. Chen, and Q. G. Zong. "Energetic ion observations of the Earth’s magnetic cusps during an extended geomagnetically quiescent period in April 2001 using detectors on S/C ISTP/Polar." Advances in Space Research 36, no. 10 (January 2005): 1946–50. http://dx.doi.org/10.1016/j.asr.2004.07.015.

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29

Escoubet, C. P., A. Masson, H. Laakso, and M. L. Goldstein. "Recent highlights from Cluster, the first 3-D magnetospheric mission." Annales Geophysicae 33, no. 10 (October 2, 2015): 1221–35. http://dx.doi.org/10.5194/angeo-33-1221-2015.

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Abstract. The Cluster mission has been operated successfully for 14 years. During this time period, the evolution of the orbit has enabled Cluster to sample many more magnetospheric regions than was initially anticipated. So far, the separation of the Cluster spacecraft has been changed more than 30 times and has ranged from a few kilometres up to 36 000 km. These orbital changes have enabled the science team to address a wide variety of scientific objectives in key regions of Earth's geospace environment: the solar wind and bow shock, the magnetopause, polar cusps, magnetotail, plasmasphere and the auroral acceleration region. Recent results have shed new light on solar wind turbulence. They showed that the magnetosheath can be asymmetric under low Mach number and that it can contain density enhancement that may affect the magnetosphere. The magnetopause was found to be thinner and to have a higher current density on the duskside than on the dawnside. New methods have been used to obtain characteristic of the magnetotail current sheet and high-temporal-resolution measurements of electron pitch angle within flux transfer events (FTEs). Plasmaspheric wind has been discovered, and the refilling of the plasmasphere was observed for the first time over a very wide range of L shells. New models of global electric and magnetic fields of the magnetosphere have been obtained where Cluster, due to its polar orbit, has been essential. Finally, magnetic reconnection was viewed for the first time with high-resolution wave and electron measurements and acceleration of plasma was observed during times of varying rate of magnetic reconnection. The analysis of Cluster data was facilitated by the creation of the Cluster Science Data System (CSDS) and the Cluster Science Archive (CSA). Those systems were implemented to provide, for the first time for a plasma physics mission, a long-term public archive of all calibrated high-resolution data from all instruments.

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30

Escoubet, C. P., M. G. G. T. Taylor, A. Masson, H. Laakso, J. Volpp, M. Hapgood, and M. L. Goldstein. "Dynamical processes in space: Cluster results." Annales Geophysicae 31, no. 6 (June 13, 2013): 1045–59. http://dx.doi.org/10.5194/angeo-31-1045-2013.

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Abstract. After 12 years of operations, the Cluster mission continues to successfully fulfil its scientific objectives. The main goal of the Cluster mission, comprised of four identical spacecraft, is to study in three dimensions small-scale plasma structures in key plasma regions of the Earth's environment: solar wind and bow shock, magnetopause, polar cusps, magnetotail, plasmasphere and auroral zone. During the course of the mission, the relative distance between the four spacecraft has been varied from 20 km to 36 000 km to study the scientific regions of interest at different scales. Since summer 2005, new multi-scale constellations have been implemented, wherein three spacecraft (C1, C2, C3) are separated by 10 000 km, while the fourth one (C4) is at a variable distance ranging between 20 km and 10 000 km from C3. Recent observations were conducted in the auroral acceleration region with the spacecraft separated by 1000s km. We present highlights of the results obtained during the last 12 years on collisionless shocks, magnetopause waves, magnetotail dynamics, plasmaspheric structures, and the auroral acceleration region. In addition, we highlight Cluster results on understanding the impact of Coronal Mass Ejections (CME) on the Earth environment. We will also present Cluster data accessibility through the Cluster Science Data System (CSDS), and the Cluster Active Archive (CAA), which was implemented to provide a permanent and public archive of high resolution Cluster data from all instruments.

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31

Russell, C. T. "The polar cusp." Advances in Space Research 25, no. 7-8 (January 2000): 1413–24. http://dx.doi.org/10.1016/s0273-1177(99)00653-5.

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32

Akasofu, S. I. "The polar cusp." Planetary and Space Science 34, no. 11 (November 1986): 1167. http://dx.doi.org/10.1016/0032-0633(86)90030-9.

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33

Eather, R. H. "Polar cusp dynamics." Journal of Geophysical Research 90, A2 (1985): 1569. http://dx.doi.org/10.1029/ja090ia02p01569.

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Escoubet, C. P., M. Fehringer, and M. Goldstein. "<i>Introduction</i>The Cluster mission." Annales Geophysicae 19, no. 10/12 (September 30, 2001): 1197–200. http://dx.doi.org/10.5194/angeo-19-1197-2001.

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Abstract. The Cluster mission, ESA’s first cornerstone project, together with the SOHO mission, dating back to the first proposals in 1982, was finally launched in the summer of 2000. On 16 July and 9 August, respectively, two Russian Soyuz rockets blasted off from the Russian cosmodrome in Baikonour to deliver two Cluster spacecraft, each into their proper orbit. By the end of August 2000, the four Cluster satellites had reached their final tetrahedral constellation. The commissioning of 44 instruments, both individually and as an ensemble of complementary tools, was completed five months later to ensure the optimal use of their combined observational potential. On 1 February 2001, the mission was declared operational. The main goal of the Cluster mission is to study the small-scale plasma structures in three dimensions in key plasma regions, such as the solar wind, bow shock, magnetopause, polar cusps, magnetotail and the auroral zones. With its unique capabilities of three-dimensional spatial resolution, Cluster plays a major role in the International Solar Terrestrial Program (ISTP), where Cluster and the Solar and Heliospheric Observatory (SOHO) are the European contributions. Cluster’s payload consists of state-of-the-art plasma instrumentation to measure electric and magnetic fields from the quasi-static up to high frequencies, and electron and ion distribution functions from energies of nearly 0 eV to a few MeV. The science operations are coordinated by the Joint Science Operations Centre (JSOC), at the Rutherford Appleton Laboratory (UK), and implemented by the European Space Operations Centre (ESOC), in Darmstadt, Germany. A network of eight national data centres has been set up for raw data processing, for the production of physical parameters, and their distribution to end users all over the world. The latest information on the Cluster mission can be found at http://sci.esa.int/cluster/.

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35

MacDougall, J., and P. T. Jayachandran. "Polar cap influx." Annales Geophysicae 23, no. 5 (July 28, 2005): 1755–61. http://dx.doi.org/10.5194/angeo-23-1755-2005.

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Abstract. This study uses digital ionosonde data from a cusp latitude station (Cambridge Bay, 77° CGM lat.) to study the convection into the polar cap. Days when the IMF magnetic field was relatively steady were used. On many days it was possible to distinguish an interval near noon MLT when the ionosonde data had a different character from that at earlier and later times. Based on our data, and other published measurements, we used the interval 10:00-13:00 MLT as the cusp interval and calculated the convection into the polar cap in this interval. The integrated convection accounted for only ~1/3 of the open polar cap flux. If the convection through the prenoon/postnoon regions on either side of the cusp was calculated the remaining 2/3 of the flux could be accounted for. The characteristics of the prenoon/postnoon regions were different from the cusp region, and we attribute this to transient flank merging versus more steady frontside merging for the cusp. Keywords. Ionosphere (Plasma convection) Magnetospheric physics (Polar cap phenomenon)

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36

Lepidi, Stefania, Patrizia Francia, Lili Cafarella, Domenico Di Mauro, and Martina Marzocchetti. "Determining the Polar Cusp Longitudinal Location from Pc5 Geomagnetic Field Measurements at a Pair of High Latitude Stations." Proceedings of the International Astronomical Union 13, S335 (July 2017): 139–41. http://dx.doi.org/10.1017/s174392131701002x.

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AbstractWe use low frequency geomagnetic field measurements at two Antarctic stations to statistically investigate the longitudinal location of the polar cusp. The two stations are both located in the polar cap at a geomagnetic latitude close to the cusp latitude; they are separated by one hour in magnetic local time. At each station the Pc5 power maximizes when the station approaches the cusp, i.e. around magnetic local noon. The comparison between the Pc5 power at the two stations allows to determine the longitudinal location of the cusp. Our analysis is conducted considering separately different orientation of the interplanetary magnetic field. The results, which indicate longitudinal shifts of the polar cusp depending on the selected conditions, are discussed in relation to previous studies of the polar cusp location based on polar magnetospheric satellite data.

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37

Saunders, Mark. "The polar cusp ionosphere: a window on solar wind–magnetosphere coupling." Antarctic Science 1, no. 3 (September 1989): 193–203. http://dx.doi.org/10.1017/s0954102089000313.

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The polar cusp ionosphere is an important part of near-Earth space which is best monitored by ground-based observations made in the remote polar regions. Antarctica seems certain to play a key role in its future exploration. The region is characterized by the direct entry of solar wind particles along magnetic field lines projecting to the dayside magnetopause (outer boundary of the magnetosphere). Thus the polar cusp ionosphere provides a splendid window for examining processes transferring solar wind mass and momentum to the magnetosphere. The review will emphasize this aspect of polar cusp ionosphere research, an area where the pace of recent work has been rapid. New results highlight the relevance of both the interplanetary magnetic field direction and changes in solar wind pressure for dynamic effects in the polar cusp ionosphere. These phenomena include surges in plasma flow, auroral activity, magnetic impulses and field-aligned (Birkeland) currents. Among the theoretical advances emerging just this past year are ones for the origin of plasma transport in the dayside polar ionosphere and for the source of the dayside Region 1 and cusp Birkeland currents.

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38

Burch, J. L. "Quasi-neutrality in the polar cusp." Geophysical Research Letters 12, no. 7 (July 1985): 469–72. http://dx.doi.org/10.1029/gl012i007p00469.

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39

EGELAND, A., and P. E. SANDHOLT. "Characteristics of the Polar Cusp Region." Annals of the New York Academy of Sciences 452, no. 1 (October 1985): 96–113. http://dx.doi.org/10.1111/j.1749-6632.1985.tb30003.x.

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40

Olson, John V. "ULF signatures of the polar cusp." Journal of Geophysical Research 91, A9 (1986): 10055. http://dx.doi.org/10.1029/ja091ia09p10055.

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41

Sandholt, P. E., C. J. Farrugia, S. W. H. Cowley, M. Lester, and J. C. Cerisier. "Excitation of transient lobe cell convection and auroral arc at the cusp poleward boundary during a transition of the interplanetary magnetic field from south to north." Annales Geophysicae 19, no. 5 (May 31, 2001): 487–93. http://dx.doi.org/10.5194/angeo-19-487-2001.

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Abstract. We document the activation of transient polar arcs emanating from the cusp within a 15 min long intermediate phase during the transition from a standard two-cell convection pattern, representative of a strongly southward interplanetary magnetic field (IMF), to a "reverse" two-cell pattern, representative of strongly northward IMF conditions. During the 2–3 min lifetime of the arc, its base in the cusp, appearing as a bright spot, moved eastward toward noon by ~ 300 km. As the arc moved, it left in its "wake" enhanced cusp precipitation. The polar arc is a tracer of the activation of a lobe convection cell with clockwise vorticity, intruding into the previously established large-scale distorted two-cell pattern, due to an episode of localized lobe reconnection. The lobe cell gives rise to strong flow shear (converging electric field) and an associated sheet of outflowing field-aligned current, which is manifested by the polar arc. The enhanced cusp precipitation represents, in our view, the ionospheric footprint of the lobe reconnection process.Key words. Magnetospheric physics (auroral phenomena; magnetopause, cusp, and boundary layers; plasma convection)

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42

Carlson, H. C., K. Oksavik, and J. Moen. "On a new process for cusp irregularity production." Annales Geophysicae 26, no. 9 (September 23, 2008): 2871–85. http://dx.doi.org/10.5194/angeo-26-2871-2008.

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Abstract. Two plasma instability mechanisms were thought until 2007 to dominate the formation of plasma irregularities in the F region high latitude and polar ionosphere; the gradient-drift driven instability, and the velocity-shear driven instability. The former mechanism was accepted as accounting for plasma structuring in polar cap patches, the latter for plasma structuring in polar cap sun aligned arcs. Recent work has established the need to replace this view of the past two decades with a new patch plasma structuring process (not a new mechanism), whereby shear-driven instabilities first rapidly structure the entering plasma, after which gradient drift instabilities build on these large "seed" irregularities. Correct modeling of cusp and early polar cap patch structuring will not be accomplished without allowing for this compound process. This compound process explains several previously unexplained characteristics of cusp and early polar cap patch irregularities. Here we introduce additional data, coincident in time and space, to extend that work to smaller irregularity scale sizes and relate it to the structured cusp current system.

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43

Laakso, H., R. Pfaff, and P. Janhunen. "Polar observations of electron density distribution in the Earth’s magnetosphere. 2. Density profiles." Annales Geophysicae 20, no. 11 (November 30, 2002): 1725–35. http://dx.doi.org/10.5194/angeo-20-1725-2002.

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Abstract. Using spacecraft potential measurements of the Polar electric field experiment, we investigate electron density variations of key plasma regions within the magnetosphere, including the polar cap, cusp, trough, plasmapause, and auroral zone. The statistical results were presented in the first part of this study, and the present paper reports detailed structures revealed by individual satellite passes. The high-altitude (> 3 RE) polar cap is generally one of the most tenuous regions in the magnetosphere, but surprisingly, the polar cap boundary does not appear as a steep density decline. At low altitudes (1 RE) in summer, the polar densities are very high, several 100 cm-3 , and interestingly, the density peaks at the central polar cap. On the noonside of the polar cap, the cusp appears as a dense, 1–3° wide region. A typical cusp density above 4 RE distance is between several 10 cm-3 and a few 100 cm-3 . On some occasions the cusp is crossed multiple times in a single pass, simultaneously with the occurrence of IMF excursions, as the cusp can instantly shift its position under varying solar wind conditions, similar to the magnetopause. On the nightside, the auroral zone is not always detected as a simple density cavity. Cavities are observed but their locations, strengths, and sizes vary. Also, the electric field perturbations do not necessarily overlap with the cavities: there are cavities with no field disturbances, as well as electric field disturbances observed with no clear cavitation. In the inner magnetosphere, the density distributions clearly show that the plasmapause and trough densities are well correlated with geomagnetic activity. Data from individual orbits near noon and midnight demonstrate that at the beginning of geomagnetic disturbances, the retreat speed of the plasmapause can be one L-shell per hour, while during quiet intervals the plasmapause can expand anti-earthward at the same speed. For the trough region, it is found that the density tends to be an order of magnitude higher on the day-side (~1 cm-3) than on the nightside (~0.1–1 cm-3), particularly during low Kp.Key words. Magnetospheric physics (auroral phenomena; plasmasphere; polar cap phenomena)

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44

Rae, I. J., M. Lester, S. E. Milan, T. A. Fritz, M. Grande, and J. D. Scudder. "Polar observations of the time-varying cusp." Journal of Geophysical Research: Space Physics 106, A9 (September 1, 2001): 19057–65. http://dx.doi.org/10.1029/2000ja003015.

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Arridge, C. S., J. M. Jasinski, N. Achilleos, Y. V. Bogdanova, E. J. Bunce, S. W. H. Cowley, A. N. Fazakerley, et al. "Cassini observations of Saturn's southern polar cusp." Journal of Geophysical Research: Space Physics 121, no. 4 (April 2016): 3006–30. http://dx.doi.org/10.1002/2015ja021957.

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46

Farrell, W. M., R. P. Lepping, and C. W. Smith. "ULF turbulence in the Neptunian polar cusp." Journal of Geophysical Research: Space Physics 98, A3 (March 1, 1993): 3631–43. http://dx.doi.org/10.1029/92ja02204.

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47

Engebretson, M. J., and J. T. Nelson. "Atomic nitrogen densities near the polar cusp." Journal of Geophysical Research 90, A9 (1985): 8407. http://dx.doi.org/10.1029/ja090ia09p08407.

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Fritz, T. A., Jiasheng Chen, Robert B. Sheldon, Harlan E. Spence, Joseph F. Fennell, Stefano Livi, Christopher T. Russell, and Jolene S. Pickett. "Cusp energetic particle events measured by POLAR spacecraft." Physics and Chemistry of the Earth, Part C: Solar, Terrestrial & Planetary Science 24, no. 1-3 (January 1999): 135–40. http://dx.doi.org/10.1016/s1464-1917(98)00020-8.

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Sandholt, P. E. "Dayside polar cusp/cleft aurora: Morphology and dynamics." Physics and Chemistry of the Earth 22, no. 7-8 (January 1997): 675–84. http://dx.doi.org/10.1016/s0079-1946(97)00195-x.

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Palmaerts, B., A. Radioti, E. Roussos, D. Grodent, J. C. Gérard, N. Krupp, and D. G. Mitchell. "Pulsations of the polar cusp aurora at Saturn." Journal of Geophysical Research: Space Physics 121, no. 12 (December 2016): 11,952–11,963. http://dx.doi.org/10.1002/2016ja023497.

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Journal articles on the topic 'Polar cusps'

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