Thermospheric density enhancements in the dayside cusp region during strong B_Y conditions

Abstract

Tri‐axial accelerometer data from the Challenging Minisatellite Payload (CHAMP) satellite have revealed the thermospheric density and its variability in unprecedented detail. The data often contain regions of high density located in the cusp sector at high latitudes. In this paper we provide the first detailed explanation of a high latitude density enhancement observed by CHAMP, focusing on the August 24, 2005 interval. The Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIMEGCM) was driven by high‐fidelity high‐latitude inputs specified by the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) algorithm, and reproduced the main features of the density enhancements. The TIMEGCM and AMIE provide a global framework for interpretation of the CHAMP densities. Our simulations reveal that the observed density enhancement in the dayside cusp region resulted from unexpectedly large amounts of energy entering the Ionosphere‐Thermosphere system at cusp latitudes during an interval of strong (+20 nT) BY.

Studies of ionospheric F-region response in the Latin American sector during the geomagnetic storm of 21–22 January 2005

“…Specifically, the high latitude particle and convection forcing is specified by the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) technique. AMIE assimilates magnetometer, DMSP and SuperDARN data to produce the electrodynamic specification (see Crowley et al, 2010) used by the TIME-GCM. AMIE is run at a 5 min cadence, and so the TIME-GCM is able to capture much of the variability in the forcing.…”

“…Lee et al (2010) in their recent paper entitled "Can intense substorms occur under northward IMF conditions" mention that the occurrence of such (intense) substorms implies that a certain (large) amount of energy remains in the tail even under northward IMF conditions. Crowley et al (2010) also showed that large amounts of energy can be deposited into the high latitude regions during B z northward or strong B y conditions, driving large perturbations in the neutral density at times when they would not previously have been expected. However, they argue that the energy is deposited as a result of reconnection in the lobes under B z northward or strong B y conditions, and not stored in the tail.…”

“…The dominance occurs when the vertical (downward) component of the field-aligned plasma flow is greater than the vertical (upward) component of the E × B drift. Also, the observed ionospheric parameters during the storm at different stations are compared with from the TIME-GCM (ThermosphereIonosphere-Mesosphere-Electrodynamics General Circulation Model) (Roble and Ridley, 1994;Crowley et al, 1999Crowley et al, , 2010 simulation results. Figure 2 shows the variations of the geomagnetic indices (Kp, AE, and Dst), solar wind (number density and velocity), interplanetary magnetic field (IMF -three magnetic field components B x , B y , and B z ), and total magnetic field (B), observed on UT days 21 and 22 January.…”

Alfvén Mach number and IMF clock angle dependencies of sunward flow channels in the magnetosphere

“…It remains to be seen whether the magnitude of the corresponding ionospheric ExB drift within sunward flow channels and the embedded Poynting flux directly correlates with M A in the solar wind. It is likely that sunward flow channels and enhanced Poynting fluxes exist in the ionosphere during these low M A solar wind conditions which is potentially very important for neutral density enhancements in low Earth orbit and the resulting increased satellite drag [Lühr et al, 2004;Crowley et al, 2010].…”

“…Crowley et al [2010] used the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure for one of these anomalous events and verified that the high 60 mW/m 2 values of localized Joule heating were present at the foot points of the near-cusp and polar cap field lines and associated them with heretofore unmodeled neutral density enhancements in this region [Lühr et al, 2004]. Knipp et al [2011] demonstrated that the same ExB flow channels examined by Eriksson et al [2008] were related to unprecedented and large earthward-directed Poynting fluxes at 850 km altitude.…”