Effect of the solar activity variation on the Global Ionosphere Thermosphere Model (GITM)

Davide Masutti,Aaron J Ridley,Günther March,Jan Thoemel

doi:10.5194/angeo-34-725-2016

Abstract

Abstract. The accuracy of global atmospheric models used to predict the middle/lower thermosphere characteristics is still an open topic. Uncertainties in the prediction of the gas properties in the thermosphere lead to inaccurate computations of the drag force on space objects (i.e. satellites or debris). Currently the lifetime of space objects and therefore the population of debris in low Earth orbit (LEO) cannot be quantified with a satisfactory degree of accuracy. In this paper, the Global Ionosphere Thermosphere Model (GITM) developed at the University of Michigan has been validated in order to provide detailed simulations of the thermosphere. First, a sensitivity analysis has been performed to investigate the effect of the boundary conditions on the final simulations results. Then, results of simulations have been compared with flight measurements from the CHallenging Minisatellite Payload (CHAMP) and Gravity Recovery and Climate Experiment (GRACE) satellites and with existing semi-empirical atmospheric models (IRI and MSIS). The comparison shows a linear dependency of the neutral density values with respect to the solar activity. In particular, GITM shows an over-predicting or under-predicting behaviour under high or low solar activity respectively. The reasons for such behaviour can be attributed to a wrong implementation of the chemical processes or the gas transport properties in the model.

Highlights

The thermosphere is the layer of the Earth’s atmosphere directly above the mesosphere and directly below the exosphere (90–600 km altitude)
The analysis suggests that the quality of the results obtained from Global Ionosphere Thermosphere Model (GITM) simulations are in general grid-dependent below a certain refinement threshold
Three distinct storms (Ap >= 150) impacted the thermosphere between 22 and 27 July 2004. Both the data and simulations show an increase of the neutral density by almost 1 order of magnitude

Summary

Introduction

The thermosphere is the layer of the Earth’s atmosphere directly above the mesosphere and directly below the exosphere (90–600 km altitude). These models are finely tuned to match a database of flight measurements, but when applied outside the interpolated ranges they are subjected to large uncertainties in atmosphere density and composition These uncertainties affect the orbital propagator calculation by leading to an error of several kilometres in the estimated position of LEO satellites (Vallado and Finkleman, 2014). In 2016, the QB50 mission will launch one of the biggest CubeSat constellations in order to perform multi-point measurements of the predominant species down to 200 km altitude (Thoemel et al, 2014) These scientific measurements will enhance the understanding of atmospheric characteristics in the middle and lower thermosphere and they will provide data for a more accurate validation of GCMs. In Sect.

Methodology

Validation data

Sensitivity to solar and geomagnetic variability

Comparison with flight data

Effect of the solar activity

Conclusions