Assessment of the non‐hydrostatic effect on the upper atmosphere using a general circulation model (GCM)

Abstract

Under hydrostatic equilibrium, a typical assumption used in global thermosphere ionosphere models, the pressure gradient in the vertical direction is exactly balanced by the gravity force. Using the non‐hydrostatic Global Ionosphere Thermosphere Model (GITM), which solves the complete vertical momentum equation, the primary characteristics of non‐hydrostatic effects on the upper atmosphere are investigated. Our results show that after a sudden intense enhancement of high‐latitude Joule heating, the vertical pressure gradient force can locally be 25% larger than the gravity force, resulting in a significant disturbance away from hydrostatic equilibrium. This disturbance is transported from the lower altitude source region to high altitudes through an acoustic wave, which has been simulated in a global circulation model for the first time. Due to the conservation of perturbation energy, the magnitude of the vertical wind perturbation increases with altitude and reaches 150 (250) m/s at 300 (430) km during the disturbance. The upward neutral wind lifts the atmosphere and raises the neutral density at high altitudes by more than 100%. These large vertical winds are not typically reproduced by hydrostatic models of the thermosphere and ionosphere. Our results give an explanation of the cause of such strong vertical winds reported in many observations.

Solar wind interaction with the Martian upper atmosphere: Crustal field orientation, solar cycle, and seasonal variations

“…Therefore, currently M-GITM does not include the calculation of hydrogen. There is no hydrostatic assumption in this model; thus, it can deal with large vertical velocities [Ridley et al, 2006;Deng et al, 2008]. It is noteworthy that the previous Mars Thermospheric General Circulation Model (M-TGCM) is based on the hydrostatic assumption [ Bougher et al, 2000Bougher et al, , 2006 and thus cannot deal with large vertical winds appropriately, especially when experiencing extreme events, such as interplanetary coronal mass ejections (ICMEs) and solar energetic particles (SEPs) heating.…”

Simulation of non-hydrostatic gravity wave propagation in the upper atmosphere

“…GITM can also be run both globally and regionally. One limitation of GITM is the small time step (2-3 s), due to its explicit solver and the presence of vertically propagating acoustic waves in the solution (Deng et al, 2008), while other hydrostatic implicit GCMs may be run with much larger time steps (2-5 min).…”

“…Upper atmospheric non-hydrostatic models (Chang and St.-Maurice, 1991;Deng et al, 2008Deng et al, , 2011 showed that sudden enhancements of Joule heating during geomagnetically disturbed periods generate intensive acoustic waves. Meanwhile, significant amounts of energy are deposited in the thermosphere through the acoustic waves propagating from the lower atmosphere (Hickey et al, 2001;Rind, 1977).…”

Retrospective-Cost Subsystem Identification for the Global Ionosphere-Thermosphere Model

“…These extensions are based on the improved retrospective cost algorithm given in [8], which requires less modeling information than prior versions of this algorithm. This distinction is crucial for GITM, which is a highly nonlinear simulation code, whereas RCSI was originally developed in [5] for linear models.…”

“…The grid structure within GITM is fully parallel and covers the entire surface of the Earth by using a block-based two-dimensional domain decomposition in the horizontal coordinates [5]. The number of latitude and longitude blocks can be specified at run time in order to modify the horizontal resolution.…”