Gravity waves simulated by high‐resolution Whole Atmosphere Community Climate Model

Abstract

For the first time a mesoscale-resolving whole atmosphere general circulation model has been developed, using the National Center for Atmospheric Research Whole Atmosphere Community Climate Model with ∼0.25 • horizontal resolution and 0.1 scale height vertical resolution above the middle stratosphere (higher resolution below). This is made possible by the high accuracy and high scalability of the spectral element dynamical core from the High-Order Method Modeling Environment. For the simulated January-February period, the latitude-height structure and the magnitudes of the temperature variance compare well with those deduced from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) observations. The simulation reveals the increasing dominance of gravity waves (GWs) at higher altitudes through both the height dependence of the kinetic energy spectra, which display a steeper slope (∼ −3) in the stratosphere and an increasingly shallower slope above, and the increasing spatial extent of GWs (including a planetary-scale extent of a concentric GW excited by a tropical cyclone) at higher altitudes. GW impacts on the large-scale flow are evaluated in terms of zonal mean zonal wind and tides: with no GW drag parameterized in the simulations, forcing by resolved GWs does reverse the summer mesospheric wind, albeit at an altitude higher than climatology, and only slows down the winter mesospheric wind without closing it. The hemispheric structures and magnitudes of diurnal and semidiurnal migrating tides compare favorably with observations.

Gravity Wave Variation from the Troposphere to the Lower Thermosphere during a Stratospheric Sudden Warming Event: A Case Study

“…Two major SSW cases are identified in the simulations, one in February and one in November-December, and the former is analyzed in this study. The GW potential energy density and absolute momentum flux deduced from the simulation are in general agreement with satellite observations (Liu et al 2014b;Liu 2016), though the zonal wind reversal produced by the resolved GW occurs at altitudes higher than climatology.…”

“…1), including the development of the elevated stratopause, changes in the mesosphere and lower thermosphere and inter-hemispheric coupling patterns (downward shift of eastward acceleration near 80km at mid to high southern latitudes, cooling at similar location while warming above), are similar to those obtained in previous studies (mostly using parameterized GW). As discussed in Liu et al (2014b), the resolved gravity waves in the model are not sufficiently strong and their breaking altitudes are too high. Therefore, the mesopause and stratopause heights are higher than climatology.…”

“…WACCM used in the current study is the same as that described in Liu et al (2014b): it employs the spectral element (SE) dynamical core based on a cubed-sphere with a quasi-uniform horizontal resolution of ~25 km (NE120NP4). The vertical resolution is 0.1 scale-height above 40hPa and the model has 209 levels (L209), extending to 5.9 × 10 −6 hPa (~145 km).…”

“…With a quasi-uniform horizontal resolution of ~25 km and vertical resolution of 0.1 scale-height, the model can resolve waves with horizontal wavelengths down to ~200 km without excessive numerical damping (Liu et al 2014b). WACCM model and simulations used for this study and the analysis method are described in Section 2.…”

Medium-scale traveling ionospheric disturbances over Taiwan observed with HF Doppler sounding

“…Hence, including their parametrization into atmospheric models is required (Liu et al 2014). They also play an important role in the energy budget of the lower thermosphere, and transport momentum and energy from lower to higher atmospheric layers (Laštovička 2009).…”