10 Feb 2022
10 Feb 2022
Status: a revised version of this preprint is currently under review for the journal ANGEO.

Storm time polar cap expansion: IMF clock angle dependence

Beket Tulegenov1, Joachim Raeder1, William Douglas Cramer1, Banafsheh Ferdousi1, Timothy Fuller-Rowell2, Naomi Maruyama3, and Robert Strangeway4 Beket Tulegenov et al.
  • 1Space Science Center, University of New Hampshire, Durham, NH, USA
  • 2Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA
  • 3NOAA Space Weather Prediction Center, Boulder, CO, USA
  • 4University of California, Los Angeles, CA, USA

Abstract. It is well known that the polar cap, delineated by the Open Closed field line Boundary (OCB), responds to changes in the Interplanetary Magnetic Field (IMF). In general, the boundary moves equatorward when the IMF turns southward and contracts poleward when the IMF turns northward. However, observations of the OCB are spotty and limited in local time, making more detailed studies of its IMF dependence difficult. Here, we simulate five solar storm periods with the coupled model consisting of the Open Geospace General Circulation model (OpenGGCM) coupled with Coupled Thermosphere Ionosphere Model (CTIM) and the Rice Convection Model (RCM), i.e., the OpenGGCM-CTIM-RCM model, to estimate the location and dynamics of the OCB. For these events, polar cap boundary location observations are also obtained from Defense-Meteorological Satellite Program (DMSP) precipitation spectrograms and compared with the model output. There is a large scatter in the DMSP observations and in the model output. However, we generally find good agreement between the model and the observations. On average, the model overestimates the latitude of the open-closed field line boundary by 1.61 degrees. Additional analysis of the simulated polar cap boundary dynamics across all local times shows that the MLT of the largest polar cap expansion closely correlates with the IMF clock angle; that the strongest correlation occurs when the IMF is southward; that during strong southward IMF the polar cap shifts sunward; and that the polar cap rapidly contracts at all local times when the IMF turns northward.

Beket Tulegenov et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on angeo-2022-9', Anonymous Referee #1, 04 Mar 2022
    • AC2: 'Reply on RC1', Joachim Raeder, 16 May 2022
  • RC2: 'Comment on angeo-2022-9', Anonymous Referee #2, 11 Mar 2022
    • AC1: 'Reply on RC2', Joachim Raeder, 16 May 2022

Beket Tulegenov et al.

Beket Tulegenov et al.


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Short summary
We study how the polar regions of the earth connect to space along magnetic field lines. While the earth's magnetic field is mostly of the shape of a dipole, at high latitudes the field lines tend to be open and connect to interplanetary space. This area of open field line is called the polar cap and it is highly dynamic. We find through data analysis and computer simulations that the shape of the polar cap is closely controlled by the magnetic field embedded in the solar wind.