Mapping Of Ionospheric Electrodynamics Procedure Research Articles

Inverse procedure for high‐latitude ionospheric electrodynamics: Analysis of satellite‐borne magnetometer data

AbstractThis paper presents an analysis of data from the magnetometers on board the Defense Meteorological Satellite Program (DMSP) F‐15, F‐16, F‐17, and F‐18 satellites and the Iridium satellite constellation, using an inverse procedure for high‐latitude ionospheric electrodynamics, during the period of 29–30 May 2010. The Iridium magnetometer data are made available through the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) program. The method presented here is built upon the assimilative mapping of ionospheric electrodynamics procedure but with a more complete treatment of the prior model uncertainty to facilitate an optimal inference of complete polar maps of electrodynamic variables from irregularly distributed observational data. The procedure can provide an objective measure of uncertainty associated with the analysis. The cross‐validation analysis, in which the DMSP data are used as independent validation data sets, suggests that the procedure yields the spatial prediction of DMSP perturbation magnetic fields from AMPERE data alone with a median discrepancy of 30–50 nT. Discrepancies larger than 100 nT are seen in about 20% of total samples, whose location and magnitude are generally consistent with the previously identified discrepancy between DMSP and AMPERE data sets. Resulting field‐aligned current (FAC) patterns exhibit more distinct spatial patterns without spurious high‐frequency oscillatory features in comparison to the FAC products provided by AMPERE. Maps of the toroidal magnetic potential and FAC estimated from both AMPERE and DMSP data under four distinctive interplanetary magnetic field (IMF) conditions during a magnetic cloud event demonstrate the IMF control of high‐latitude electrodynamics and the opportunity for future scientific investigation.

Upper thermospheric responses to forcing from above and below during 1–10 April 2010: Results from an ensemble of numerical simulations

AbstractIn this report we examine the spatial and temporal variability of the quiescent thermosphere leading up to and after the 5 April 2010 geomagnetic disturbance. We attribute the dominant driver of this variability to a combination of tides generated in situ and in the troposphere, stratosphere, and mesosphere. We identify nonmigrating tidal signatures attributable to the latter source that are ubiquitous, persistent, and significant at all thermospheric latitudes. Further, these perturbations underlie the upper atmospheric response to solar geomagnetic disturbances and are measurably altered, along with their migrating counterparts, during the storm. Our investigation is centered on a series of National Center for Atmospheric Research thermosphere‐ionosphere‐mesosphere‐electrodynamics general circulation model simulations during 1–10 April 2010, including an optimal simulation with lower boundary forcing based on Modern‐Era Retrospective Analysis for Research and Application reanalysis data and upper boundary forcing based on satellite and ground magnetometer measurements and the Assimilative Mapping of Ionospheric Electrodynamics procedure and three diagnostic simulations. The differences between the optimal and diagnostic simulations allow us to quantify thermospheric variability attributable to solar geomagnetic forcing and dynamical effects propagating into the thermosphere from below. We find that they can be comparable at high latitudes for some nonmigrating tidal components.

Nonlinear response of the polar ionosphere to large values of the interplanetary electric field

During large geomagnetic storms the polar cap potential drop fluctuates, but its average value seldom reaches 150 kV and its peak value seldom reaches 200 kV. Since the quiet time potential drop is about 40 kV and since the interplanetary electric field (IEF) is greatly enhanced during storms, this relative constancy appears to be due to a saturation effect. This apparent saturation phenomenon has been previously noted but has not received much attention in the recent literature, in spite of its importance during magnetic storms and in spite of the fact that it seems not to be understood. The IEF and the polar cap potential drop appear to have a very linear relationship up to about 80 kV. At greater IEF the potential drop increases only slightly. We use the assimilative mapping of ionospheric electrodynamics procedure to illustrate this saturation on a case‐by‐case basis during a number of recent storms. We confirm using DE 2 data that the saturation of the potential drop is a real effect and is not an artifact of the measurement process. Observations of the plasmapause and the buildup of the ring current indicate a linear response to the IEF over a wide range of solar wind conditions. Thus the convection of the magnetospheric plasma and the injection of energy into the ring current seem not to be affected by this saturation.

High‐latitude ionospheric electrodynamics as determined by the assimilative mapping of ionospheric electrodynamics procedure for the conjunctive SUNDIAL/ATLAS 1/GEM period of March 28–29, 1992

During the conjunctive SUNDIAL/ATLAS 1/GEM campaign period of March 28–29, 1992, a set of comprehensive data has been collected both from space and from ground. The assimilative mapping of ionospheric electrodynamics (AMIE) procedure is used to derive the large‐scale high‐latitude ionospheric conductivity, convection, and other related quantities, by combining the various data sets. The period was characterized by several moderate substorm activities. Variations of different ionospheric electrodynamic fields are examined for one substorm interval. The cross‐polar‐cap potential drop, Joule heating, and field‐aligned current are all enhanced during the expansion phase of substorms. The most dramatic changes of these fields are found to be associated with the development of the substorm electrojet in the post midnight region. Variations of global electrodynamic quantities for this 2‐day period have revealed a good correlation with the auroral electrojet (AE) index. In this study we have calculated the AE index from ground magnetic perturbations observed by 63 stations located between 55° and 76° magnetic latitudes north and south, which is larger than the standard AE index by about 28% on the average over these 2 days. Different energy dissipation channels have also been estimated. On the average over the 2 days, the total globally integrated Joule heating rate is about 102 GW and the total globally integrated auroral energy precipitation rate is about 52 GW. Using an empirical formula, the ring current energy injection rate is estimated to be 125 GW for a decay time of 3.5 hours, and 85 GW for a decay time of 20 hours. We also find an energy‐coupling efficiency of 3% between the solar wind and the magnetosphere for a southward interplanetary magnetic field (IMF) condition.