Browsing by Author "Fang, T. W."

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    A whole atmosphere model simulation of the impact of a sudden stratospheric warming on thermosphere dynamics and electrodynamics
    (American Geophysical Union, 2010-10-15) Fuller‐Rowell, T.; Wu, Fei; Akmaev, Rashid; Fang, T. W.; Araujo‐Pradere, Eduardo
    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.
    Palabras clave:Sudden stratospheric warmingThermosphere electrodynamicsAtmospheric modeling
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    First forecast of a sudden stratospheric warming with a coupled whole‐atmosphere/ionosphere model IDEA
    (American Geophysical Union, 2014-03-10) Wang, H.; Akmaev, R. A.; Fang, T. W.; Fuller-Rowell, T. J.; Wu, F.; Maruyama, N.; Iredell, M. D.
    We present the first “weather forecast” with a coupled whole‐atmosphere/ionosphere model of Integrated Dynamics in Earth's Atmosphere (IDEA) for the January 2009 Sudden Stratospheric Warming (SSW). IDEA consists of the Whole Atmosphere Model and Global Ionosphere‐Plasmasphere model. A 30 day forecast is performed using the IDEA model initialized at 0000 UT on 13 January 2009, 10 days prior to the peak of the SSW. IDEA successfully predicts both the time and amplitude of the peak warming in the polar cap. This is about 2 days earlier than the National Centers for Environmental Prediction operational Global Forecast System terrestrial weather model forecast. The forecast of the semidiurnal, westward propagating, zonal wave number 2 (SW2) tide in zonal wind also shows an increase in the amplitude and a phase shift to earlier hours in the equatorial dynamo region during and after the peak warming, before recovering to their prior values about 15 days later. The SW2 amplitude and phase changes are shown to be likely due to the stratospheric ozone and/or circulation changes. The daytime upward plasma drift and total electron content in the equatorial American sector show a clear shift to earlier hours and enhancement during and after the peak warming, before returning to their prior conditions. These ionospheric responses compare well with other observational studies. Therefore, the predicted ionospheric response to the January 2009 SSW can be largely explained in simple terms of the amplitude and phase changes of the SW2 zonal wind in the equatorial E region.
    Palabras clave:Space weather forecastSudden stratospheric warmingSemidiurnal tide