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Akmaev: WHOLE ATMOSPHERE MODELING RG4004 RG4004 Akmaev: WHOLE ATMOSPHERE MODELING RG4004 RG4004 3 of 30 Akmaev: WHOLE ATMOSPHERE MODELING RG4004 RG4004 Akmaev: WHOLE ATMOSPHERE MODELING RG4004 RG4004 6 of 30 Akmaev: WHOLE ATMOSPHERE MODELING RG4004 RG4004 7 of 30

[1] A Whole Atmosphere Model (WAM) has been used to explore the possible physical connection between a sudden stratospheric warming (SSW) and the dynamics and electrodynamics of the lower thermosphere. WAM produces SSWs naturally without the need for external forcing. The classical signatures of an SSW appear in the model with a warming of the winter polar stratosphere, a reversal of the temperature gradient, and a breakdown of the stratospheric polar vortex. Substantial changes in the amplitude of stationary planetary wave numbers 1, 2, and 3 occur as the zonal mean zonal wind evolves. The simulations also show a cooling in the mesosphere and a warming in the lower thermosphere consistent with observations. The magnitude of this particular SSW is modest, belonging to the category of minor warming. In the lower thermosphere the amplitude of diurnal, semidiurnal, and terdiurnal, eastward and westward propagating tidal modes change substantially during the event. Since the magnitude of the warming is minor and the tidal interactions with the mean flow and planetary waves are complex, the one-to-one correspondence between tidal amplitudes in the lower thermosphere and the zonal mean and stationary waves in the stratosphere is not entirely obvious. The increase in the magnitude of the terdiurnal tide (TW3) in the lower thermosphere has the clearest correlation with the SSW, although the timing appears delayed by about three days. The fast group velocity of the long vertical wavelength TW3 tide would suggest a faster onset for the direct propagation of the tide from the lower atmosphere. It is possible that changes in the magnitude of the diurnal and semidiurnal tides, with their slower vertical propagation, may interact in the lower thermosphere to introduce a terdiurnal tide with a longer delay. An increase in TW3 in the lower thermosphere would be expected to alter the local time variation of the electrodynamic response. The day-to-day changes in the lower thermosphere winds from WAM are shown to introduce variability in the magnitude of dayside low latitude electric fields, with a tendency during the warming for the dayside vertical drift to be larger and occur earlier, and for the afternoon minimum to be smaller. The numerical simulations suggest that it is quite feasible that a major SSW, with a magnitude seen in January 2009, could cause large changes in lower thermosphere electrodynamics and hence in total electron content.Citation: Fuller-Rowell, T., F. Wu, R. Akmaev, T.-W. Fang, and E. Araujo-Pradere (2010), A whole atmosphere model simulation of the impact of a sudden stratospheric warming on thermosphere dynamics and electrodynamics,

A whole atmosphere model has been used to simulate the changes in the global atmosphere dynamics and electrodynamics during the January 2009 sudden stratospheric warming (SSW). In a companion paper, it has been demonstrated that the neutral atmosphere response to the 2009 warming can be simulated with high fidelity and can be forecast several days ahead. The 2009 warming was a major event with the polar stratospheric temperature increasing by 70 K. The neutral dynamics from the whole atmosphere model (WAM) was used to drive the response of the electrodynamics. The WAM simulation predicted a substantial increase in the amplitude of the 8‐hour terdiurnal tide in the lower thermosphere dynamo region in response to the warming, at the expense of the more typical semidiurnal tides. The increase in the terdiurnal mode had a significant impact on the diurnal variation of the electrodynamics at low latitude. The changes in the winds in the dayside ionospheric E region increased the eastward electric field early in the morning, and drove a westward electric field in the afternoon. The initial large increase in upward drifts gradually moved to later local times, and decreased in magnitude. The change in the amplitude and phase of the electrodynamic response to the SSW is in good agreement with observations from the Jicamarca radar. The agreement with observations serves to validate the whole atmosphere dynamic response. Since WAM can forecast the neutral dynamics several days ahead, the simulations indicate that the electrodynamic response can also be predicted.

[1] The upper atmosphere and ionosphere exhibit variability on spatial and temporal scales characteristic of tides and planetary waves originating in the lower atmosphere. To study their generation, vertical propagation, possible nonlinear interactions and effects a new Whole Atmosphere Model (WAM) has been developed as part of the Integrated Dynamics through Earth's Atmosphere (IDEA) project. WAM is a 150-layer general circulation model based on the US National Weather Service's operational Global Forecast System (GFS) model extended upward to cover the atmosphere from the ground to about 600 km. First simulations reveal the presence of migrating and nonmigrating tides modulated at planetary wave periods in the upper atmosphere. Comparisons with observations from the TIMED satellite in the lower thermosphere show that WAM reproduces the seasonal variability of tides remarkably well, including the diurnal eastward harmonic with zonal wavenumber 3 (DE3) recently implicated in the observed spatial morphology of the ionosphere. Citation: Akmaev, R.

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[1] The Whole Atmospheric Model (WAM) initialized with a data assimilation scheme is capable of simulating real sudden stratospheric warming (SSW) events. The electrodynamics in the Coupled Thermosphere Ionosphere and Plasmasphere with Electrodynamics model (CTIPe) was driven by the WAM thermospheric winds in January 2009 to study the response of ionospheric drifts during the SSW. Simulation results are compared with observations of the vertical drift at Jicamarca and the equatorial electrojet (EEJ) in the Asian sectors. Early morning upward drift and afternoon downward drift are reproduced in all longitudes in the simulations, and are consistent with the available observations. Results also show that the occurrence time of the early morning upward drift and afternoon downward drift have significant phase differences between different longitudes. Simulations suggest that during the SSW the longitude dependence of the amplitude and phase of the equatorial vertical plasma drift is caused by the changing magnitudes of the migrating tides modulated by the geometry of the geomagnetic field. Some additional day-to-day variability and modulation of the phase structures at different longitudes in ionospheric vertical drifts during the SSW are possibly produced by the short-term changes in the non-migrating tides and by planetary waves.

[1] Hydrostatic expansion in a gravity field of an atmospheric layer with elevated temperatures, such as the long known thermospheric midnight temperature maximum (MTM), results in a total mass density increase at a given altitude above the layer. Long-term simulations with the Whole Atmosphere Model reveal a noticeable midnight density maximum (MDM), appropriately lagging behind the MTM at the same height. The MDM magnitude, timing, and variability are in good agreement with available in-situ observations. Of particular importance is the observation of a downward phase progression of the MDM peak time obtained from the San Marco satellites and closely reproduced in the model results. This is consistent with the suggestion, made over 30 years ago, that both the MTM and MDM are driven by tidal waves, in particular, the terdiurnal tide propagating upward from the lower atmosphere and interacting with a diurnally varying ion drag. The accompanying wind variations are also found in good agreement with radar observations, which first related them to the nighttime ionosphere collapse in the early 1970s.