Global Ionosphere Thermosphere Research Articles

Statistical Characterization of GITM Thermospheric Horizontal Winds in Comparison to GOCE Estimations

AbstractCharacterization of the thermospheric horizontal wind is an important challenge in atmospheric modeling due to its vital role in the transport of densities and energy, associations with the diurnal tide, and interplay with vertical winds that drive changes in the thermosphere neutral composition. The mechanisms and drivers that underlie the physics of thermospheric horizontal winds remain under investigation and, to date, no comprehensive statistical study between thermospheric winds generated by a physics‐based atmospheric model and those retrieved from satellite measurements has been performed. Comparisons between cross‐track horizontal winds from a 10‐month run of Global Ionosphere‐Thermosphere (GITM) and those derived from the Gravity field and steady‐state Ocean Circulation Explorer (GOCE) satellite show that GITM did best modeling horizontal winds in the polar zone but overestimated horizontal wind speeds at midlatitudes just outside of the equatorial ionization anomaly region. GITM's wind response to AE was best at polar noon and worst in the midnight auroral zone, its ability to capture seasonality was best in the northern high latitudes and worst in the southern high latitudes, and GITM displayed less wind variability as a function of F10.7 than GOCE, matching it best for F10.7 >∼150. Discrepancies in GITM's performance may be explained by inaccurate modeling of ion drift, ion drag, and electron densities.

Revisiting Ionosphere‐Thermosphere Responses to Solar Wind Driving in Superstorms of November 2003 and 2004

AbstractWe revisit three complex superstorms of 19–20 November 2003, 7–8 November 2004, and 9–11 November 2004 to analyze ionosphere‐thermosphere (IT) effects driven by different solar wind structures associated with complex interplanetary coronal mass ejections (ICMEs) and their upstream sheaths. The efficiency of the solar wind‐magnetosphere connection throughout the storms is estimated by coupling functions. The daytime IT responses to the complex driving are characterized by combining and collocating (where possible) measurements of several physical parameters (total electron content or TEC, thermospheric infrared nitric oxide emission, and composition ratio) from multiple satellite platforms and ground‐based measurements. A variety of metrics are utilized to examine global IT phenomena at ~1 h timescales. The role of direct driving of IT dynamics by solar wind structures and the role of IT preconditioning in these storms, which feature complex unusual TEC responses, are examined and contrasted. Furthermore, IT responses to ICME magnetic clouds and upstream sheaths are separately characterized. We identify IT feedback effects that can be important for long‐lasting strong storms. The role of the interplanetary magnetic field By component on ionospheric convection may not be well captured by existing coupling functions. Mechanisms of thermospheric overdamping and consequential ionospheric feedback need to be further studied.