Effect of IMF B_Y on thermospheric composition at high and middle latitudes: 1. Numerical experiments

Abstract

[1] Magnetic storms and their effects on the thermosphere and ionosphere have been studied for many years, yet there are many aspects of the thermospheric and ionospheric responses that are not understood. The purpose of this paper is to show how the high-latitude composition depends on the sign of the IMF B Y component, using controlled simulations with a global first principles model. Because the high-latitude convection and neutral wind systems are strongly controlled by the IMF B Y component, it seems likely that the compositional response that is driven by high-latitude forcing should also be sensitive to the B Y component. To date, no first-principles modeling has been performed to test the idea of IMF B Y effects on composition. Numerical experiments using model simulations provide insight into this important scientific question, since the thermospheric compositional response to the convection patterns for different IMF B Z and B Y can be studied in isolation in a model. In this paper we use a first-principles model to determine the effect of the IMF B Y component on the compositional response of the high-latitude thermosphere. We show for the first time that a clockwise rotation of the potential pattern resulting from a change from B Y -negative to B Y -positive drives a corresponding rotation in the wind, neutral density, and composition distributions. B Y control of thermospheric composition has been invoked in the literature to explain an apparent variability in the effectiveness of auroral activity in causing thermospheric storm effects at middle latitudes, as observed in global images of the far-ultraviolet (FUV) OI 130.4-nm emission from the DE-1 auroral imager. However, the effect in the simulations presented here is opposite from that suggested by earlier work based on DE data, indicating another explanation must be sought for the DE results. These simulations are highly relevant for interpreting data being provided by more modern UV imaging instruments on the DMSP, TIMED, and IMAGE satellites.

Thermospheric mass density: A review

“…Caspers and Prölss (1999) compared a selection of mass spectrometer latitudinal passes, at altitudes below 350 km, with the TIGCM modeling results of Crowley et al (1996) and Schoendorf et al (1996a,b), finding that the observations support the multiple cell patterns in the simulations, but that other interpretations of the data are possible. Crowley et al (2006) simulated northern hemisphere density at 140 and 200 km altitude using TIME-GCM with high-latitude convection patterns under different B y conditions. They found that the density cells at these altitudes rotated along with the convection pattern as B y changes from negative to positive.…”

A computationally compact representation of Magnetic‐Apex and Quasi‐Dipole coordinates with smooth base vectors

“…[35] Figure 7 shows winds near a height of 250 km simulated by the Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME-GCM) [Roble and Ridley, 1994;Crowley et al, 2006]. The results are for a geomagnetically quiet day (21 June 2004, daily Kp = 1), and were selected from the continuous four-year simulation described by Drob et al [2008].…”

Effect of IMF By on thermospheric composition at high and middle latitudes: 2. Data comparisons

“…Further corrections for solar EUV flux variations use daily measured solar 10.7‐cm radio flux as a proxy for solar EUV. DE‐1 images in this and the accompanying report [ Crowley et al , 2006] are only shown after the application of this processing technique.…”

“…It is run with the above‐specified inputs over the time frame beginning on Day 263 (20 September), 1981 and finishing at the end of Day 284 (11 October). This interval covers the two event intervals beginning on Days 267 and 280 discussed by Immel et al [1997] and noted by Crowley et al [2006]. Starting the run several days before the first event interval and running it continuously on through the second interval allows the TIMEGCM to best simulate the atmospheric conditions existing prior to the onset of significant magnetic activity.…”