Swarm in situ observations of F region polar cap patches created by cusp precipitation

High-resolution in situ measurements from the three Swarm spacecraft, in a string-of-pearls configuration, provide new insights about the combined role of flow channel events and particle impact ionization in creating F region electron density structures in the northern Scandinavian dayside cusp. We present a case of polar cap patch formation where a reconnection-driven low-density relative westward flow channel is eroding the dayside solar-ionized plasma but where particle impact ionization in the cusp dominates the initial plasma structuring. In the cusp, density features are observed which are twice as dense as the solar-ionized background. These features then follow the polar cap convection and become less structured and lower in amplitude. These are the first in situ observations tracking polar cap patch evolution from creation by plasma transport and enhancement by cusp precipitation, through entrainment in the polar cap flow and relaxation into smooth patches as they approach the nightside auroral oval.

[1]  H. Carlson,et al.  Ionospheric patch formation: Direct measurements of the origin of a polar cap patch , 2004 .

[2]  Beichen Zhang,et al.  On the importance of interplanetary magnetic field ∣By∣ on polar cap patch formation , 2011 .

[3]  Nils Olsen,et al.  The CHAOS-4 Geomagnetic Field Model , 2013 .

[4]  W. Rideout,et al.  Multiradar observations of the polar tongue of ionization , 2005 .

[5]  J. K. Bekkeng,et al.  In situ measurements of plasma irregularity growth in the cusp ionosphere , 2012 .

[6]  Q.‐H. Zhang,et al.  On the importance of interplanetary magnetic field B on polar cap patch formation , 2011 .

[7]  J. Foster.  Ionospheric signatures of magnetospheric convection , 1984 .

[8]  Mike Lockwood,et al.  Motion of the dayside polar cap boundary during substorm cycles: I. Observations of pulses in the magnetopause reconnection rate , 2005 .

[9]  Raymond A. Greenwald,et al.  Dependencies of high-latitude plasma convection: Consideration of interplanetary magnetic field, seasonal, and universal time factors in statistical patterns , 2005 .

[10]  J. King,et al.  Solar wind spatial scales in and comparisons of hourly Wind and ACE plasma and magnetic field data , 2005 .

[11]  H. Carlson,et al.  Production of polar cap electron density patches by transient magnetopause reconnection , 1992 .

[12]  Peter. Dyson,et al.  A decade of the Super Dual Auroral Radar Network (SuperDARN): scientific achievements, new techniques and future directions , 2007 .

[13]  P. T. Jayachandran,et al.  Climatology of GPS phase scintillation and HF radar backscatter for the high-latitude ionosphere under solar minimum conditions , 2011 .

[14]  H. Carlson,et al.  On the collocation between dayside auroral activity and coherent HF radar backscatter , 2000 .

[15]  H. Lühr,et al.  Swarm An Earth Observation Mission investigating Geospace , 2008 .

[16]  H. Carlson,et al.  Reversed flow events in the winter cusp ionosphere observed by the European Incoherent Scatter (EISCAT) Svalbard radar , 2007 .

[17]  I. K. Walker,et al.  On the possible role of cusp/cleft precipitation in the formation of polar-cap patches , 1999 .

[18]  P. Guzdar,et al.  Plasma patch structuring by the nonlinear evolution of the gradient drift instability in the high‐latitude ionosphere , 2004 .

[19]  Tsunoda,et al.  High-latitude F-region irregularities: a review and synthesis. Technical report, 1 January 1986-1 July 1987 , 1988 .

[20]  S. E. Pryse,et al.  EISCAT observations of plasma patches at sub-auroral cusp latitudes , 2006 .

[21]  D. Decker,et al.  Modeling the formation of polar cap patches using large plasma flows , 1996 .

[22]  S. Basu,et al.  Characteristics of plasma structuring in the cusp/cleft region at Svalbard , 1998 .

[23]  Luca Spogli,et al.  Space weather challenges of the polar cap ionosphere , 2017, 1708.08617.

[24]  P. Blelly,et al.  Electron density in the cusp ionosphere: increase or depletion? , 2003 .

[25]  Bodo W. Reinisch,et al.  F layer ionization patches in the polar cap , 1983 .

[26]  S. E. Pryse,et al.  Polar patches observed by ESR and their possible origin in the cusp region , 2000 .

[27]  J. Ruohoniemi,et al.  Climatological patterns of high-latitude convection in the Northern and Southern hemispheres: Dipole tilt dependencies and interhemispheric comparisons , 2010 .

[28]  C. Hegarty,et al.  Modeling the effects of ionospheric scintillation on GPS/Satellite‐Based Augmentation System availability , 2003 .

[29]  Hermann Lühr,et al.  Fifth‐generation lithospheric magnetic field model from CHAMP satellite measurements , 2007 .

[30]  T. A. Bekkeng,et al.  First in‐situ measurements of HF radar echoing targets , 2012 .

[31]  S. Basu,et al.  Irregularity structures in the cusp/cleft and polar cap regions , 1994 .

[32]  Michael C. Kelley,et al.  On the origin and spatial extent of high-latitude F region irregularities , 1982 .

[33]  Hermann Lühr,et al.  NOAA/NGDC candidate models for the 11th generation International Geomagnetic Reference Field and the concurrent release of the 6th generation Pomme magnetic model , 2010 .

[34]  Q.‐H. Zhang,et al.  Polar cap patch segmentation of the tongue of ionization in the morning convection cell , 2013 .

[35]  J. Moen,et al.  On the entry and transit of high-density plasma across the polar cap , 2010 .

[36]  D. B. Payne,et al.  Stereo CUTLASS - A new capability for the SuperDARN HF radars , 2004 .

[37]  Y. Otsuka,et al.  Global imaging of polar cap patches with dual airglow imagers , 2014 .

[38]  S. Wing,et al.  A new magnetic coordinate system for conjugate studies at high latitudes , 1989 .