First Palmer and Millstone Hill midlatitude conjugate observation of thermospheric winds

Abstract

The first midlatitude conjugate thermospheric wind observations in the American sector showed various degrees of conjugacy between Palmer (64°S, 64°W, magnetic latitude (MLAT) 50°S) and Millstone Hill (42.82°N, 71.5°W, MLAT 53°N) under three different geomagnetic conditions (recovery after a substorm, moderately active, and quiet). The agreement with the National Center for Atmospheric Research's Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) simulations also varies with the geomagnetic activity level. During substorm recovery, the observations at Palmer (PA) and Millstone Hill (MH) both showed strong westward zonal winds, which the standard TIEGCM greatly underestimated. Inadequate ion convection pattern size and lack of effect from Subauroral Polarization Streams (SAPS) may be the cause of the large discrepancy. The TIEGCM with a SAPS model produced stronger westward zonal winds near PA but did not change the zonal wind near MH. The empirical SAPS model needs further refinements. In general, there is better conjugacy with moderate geomagnetic activity levels. The TIEGCM also agrees better with the observations. Under geomagnetically quiet conditions, the meridional winds appear to be less conjugate. The agreement between the observations and model is reasonable. Optical conjugate observations are severely limited by the seasons and weather conditions in the two hemispheres. Yet they are necessary to understanding the thermospheric dynamics in the subauroral region and its relationship with geomagnetic activity levels. The comparisons with TIEGCM are necessary for future model improvements.

High‐latitude thermospheric wind observations and simulations with SuperDARN data driven NCAR TIEGCM during the December 2006 magnetic storm

“…Wu et al . [] compared the FPI observations from southern hemisphere to northern high latitudes at Resolute with TIEGCM simulations with HLM. Some discrepancies at high latitude between the FPI and TIEGCM were observed, which may arise from the similar source namely not including the saturation in the HLM.…”

An Auroral Boundary‐Oriented Model of Subauroral Polarization Streams (SAPS)

“…The increased friction drives westward neutral winds to upward of 500 m/s and heats up the thermosphere, which changes the vertical neutral density distribution (H. Wang et al, ; Wang, Lühr, et al, ). The predictions from coupled thermosphere/ionosphere models, which incorporate a prescription for a SAPS electric field, are, in general, more successful at reproducing observations of the subauroral thermosphere and ionosphere (Pintér et al, ; W. Wang, Talaat, et al, ; Wu et al, ).…”

“…The predictions from coupled thermosphere/ionosphere models, which incorporate a prescription for a SAPS electric field, are, in general, more successful at reproducing observations of the subauroral thermosphere and ionosphere (Pintér et al, 2006;W. Wang, Talaat, et al, 2012;Wu et al, 2014).…”

The Midlatitude Thermospheric Dynamics From an Interhemispheric Perspective

“…While the midlatitude thermosphere is the region most observed and investigated for insight into upper atmospheric dynamics (e.g., Hernandez et al, ; Hernandez & Roble, , , ; Huang et al, ; Wu et al, ; Wu et al, ), it remains least understood in many respects. Midlatitude thermospheric winds respond to lower thermospheric waves, geomagnetic activity, solar EUV conditions, and Sub‐Auroral Polarization Streams (SAPS), and vary with latitude, longitude/UT, and season (e.g.,Wang et al, ; Wang et al, ; Wang et al, ; Wang & Lühr, ; Wu, Noto, et al, ; Wu, Yuan, et al, ). It is hard to isolate and quantify the forcing that drives neutral winds and their variability in the midlatitude thermosphere.…”

“…Wu, Noto, et al () used simultaneous Millstone Hill and Palmer Fabry‐Perot interferometer (FPI) observations to examine interhemispheric wind differences. One major limitation to that study is that there were no austral summer observations at the Palmer station due to its relatively high geographic latitude (64°S).…”