Abstract
Abstract. The controls of merging electrical field, Em, and IMF (interplanetary magnetic field) magnitude, B, on the storm-time changes in upper thermospheric mass density are statistically investigated using GRACE accelerometer observations and the OMNI data of solar wind and IMF for 35 great storms during 2002–2006. It reveals the following: (1) The correlation coefficients between the air mass density changes and the parameters of Em and B are generally larger at lower latitudes than at higher latitudes, and larger in noon and midnight sectors than in dawn and dusk. (2) The most likely delay time (MLDT) of mass density changes in respect to Em is about 1.5 h (4.5 h) at high (low) latitudes, having no distinct local time dependence, while it is 6 h at middle latitudes in all the local time sectors except for noon, which is longer than at low latitudes. A similar fact of longer delay time at mid-latitude is also seen for B. The MLDTs for B at various latitudes are all local time dependent distinctly with shorter delay time in noon/midnight sector and larger in dawn/dusk. Despite of widely spread of the delay time, IMF B exhibits still larger correlation coefficients with mass density changes among the interplanetary parameters. (3) The linear control factor of B on the density changes increases for large B, in contrast to somewhat saturation trend for larger Em. (4) The influence of B and Em on the mass densities shows different behavior for different types of storms. The influence intensity of Em is much stronger for CIR-driven than for CME-driven storm, while it is not so distinct for B. On the local time asymmetry of the influence, both Em and B have largest influence at noon sector for CME-driven storms, while an obviously larger intensification of the influence is found in dawn/dusk sector during CIR storms, especially for parameter Em.
Highlights
Thermospheric total mass density is important for understanding the coupling process in the solar wind– magnetosphere–ionosphere–thermosphere system, and for predicting the atmospheric drag that is needed in precise orbit determination and tracking of low orbit satellites
Burke et al (2007) found that thermospheric total mass density observed by Gravity Recovery and Climate Experiment (GRACE) is roughly proportional to polar cap potentials and magnetospheric electric fields derived from interplanetary parameters with lag time of about 4 h
In order to find the effective and practical control parameters composed by solar wind and IMF observation data for predicting storm-time changes in thermospheric mass densities, we firstly examined the relationships between the mass density changes and various interplanetary parameters including merging electric field, various IMF components, Akasofu coupling function, solar wind speed and plasma density, solar wind dynamic pressure, and so on
Summary
Thermospheric total mass density is important for understanding the coupling process in the solar wind– magnetosphere–ionosphere–thermosphere system, and for predicting the atmospheric drag that is needed in precise orbit determination and tracking of low orbit satellites. Kwak et al (2009) studied the influences of the IMF By and Bz on observed thermospheric mass density using the high-latitude southern summer thermospheric mass density near 400 km altitude derived from accelerometer on board CHAMP They found that the difference density distributions, which are obtained by subtracting values for zero IMF from those for nonzero IMF, vary strongly with respect to the direction of IMF. They obtained a linear empirical relation between mass density averaged over two latitudinal segments (low latitude segment and mid-latitude one) and lag-time–integrated merging electric fields They suggested that the dynamic pressure may have an influence on the storm-time density enhancement by analyzing the unusual magnetic storm of 21 January 2005. The controls of the selected parameters of Em and B on the storm-time mass density changes in the upper thermosphere are investigated by using GRACE accelerometer observations, emphasizing on the varying of the control factors and delay times versus latitude and local time mainly for mid- and low latitude thermosphere
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