Variability in the thermospheric neutral mass density: A multiple model comparison

Variability in the thermospheric neutral mass density in LEO/VLEO altitudes has been investigated using outputs from five models (MSIS2.0, HASDM, WACCM-X, TIEGCM, and WAM-IPE) under different geophysical conditions: geomagnetically quiet, moderate storm and super storm. These models are selected to represent empirical, assimilation, and physics-based methods. We compared the global neutral mass density distribution and the time variations in the densities using equatorial and polar orbits at three fixed LEO/VLEO altitudes (100, 200, and 300 km) from the five models. Our key findings from the analyses are: (1) there are significant systematic biases among the model results; (2) WACCM-X, TIEGCM and HASDM peak densities are roughly consistent with each other during a super storm. However, their UT differences are up to a half day; (3) WAM-IPE and MSIS-2.0 models tend to give lower densities than other models; (4) the geomagnetic activity impact on neutral mass densities increases with altitude and it is negligible at 100 km altitude, becomes evident at 150 km, and is significant at 200 km; (5) geomagnetic storms tend to reduce the biases among the model densities The systematic biases among models are likely due to the different parameterizations, drivers and boundary conditions used in the models. A systematic evaluation of the models using multiple and cross-calibrated ground truth data sets is needed to fully address the biases and offer the insight required to improve the models.