Ruiping Ma

Nonlinear interactions between gravity waves with different wavelengths and diurnal tide

By using a compressible nonlinear two-dimensional gravity wave model, we simulate the nonlinear interactions between gravity waves (GWs) with three different vertical wavelengths and a meridional component of the diurnal tidal wind and temperature (30 degrees N, September) calculated from GSWM-00. We also compare the results with the simulation of GWs propagation in a background with zero wind. Consistent with the dispersion relation, the numerical experiments show that tidal wind reduces the vertical wavelengths of the GWs when it is in the same direction as the wave propagation, and thus increases the perturbative shear and the likelihood of instability and wave breaking, especially for waves with shorter vertical wavelengths. The breaking of GWs below the critical level can increase the amplitude of diurnal tidal wind due to the momentum deposition. Because the GW penetration height increases with vertical wavelength, the amplitude of diurnal tidal wave at higher altitudes is more likely to be affected by GWs with large vertical wavelengths. Therefore gravity wave breaking not only accelerates the mean winds, but also increases the amplitudes of the diurnal tide at various altitudes.

Seasonal and latitudinal differences of the saturation effect between ionospheric NmF2 and solar activity indices

The seasonal and latitudinal differences of the correlations between daytime ionospheric F-2 peak electron density (NmF2) and solar activity indices in the east Asian/Australian sector have been analyzed using data from 15 ionosonde stations at different geomagnetic latitudes during 1969 similar to 1990. It is found that the characteristics of the correlations between NmF2 and solar activity indices have significant seasonal and latitudinal variations and hemispheric asymmetry. At middle and high latitudes, there is a clear saturation trend in NmF2 as solar activity increases in summer. However, there is no apparent saturation trend in winter, rather a tendency of nonlinear increase of NmF2 with solar activity. This nonlinear increasing effect is more pronounced in the Northern Hemisphere. In the equatorial anomaly region, the saturation effect is stronger, and the equinox has the strongest saturation effect. All seasons considered, the equatorial anomaly region has the strongest saturation effect, followed by the magnetic equatorial region. The saturation effect becomes relatively weak at middle latitudes. At higher latitudes and in the Northern Hemisphere, there is even a trend of nonlinear increase of NmF2 with solar activity. Our results indicate that thermospheric global circulation is probably an important factor that introduces seasonal, latitudinal, and north-south differences in the correlations between NmF2 and solar activity indices.

Effects of gravity waves on the distributions of O3 and OH in the mesopause region

A dynamical-photochemical model of atmospheric gravity waves is used to study the influences of gravity waves on distributions of atmospheric minor species through transportation and photochemical reactions. We mainly study the effect of gravity waves on the distributions of atmospheric trace gases through the nonlinear photochemical reactions. O3 and OH are taken as examples in this note. The calculations indicate that the effect of gravity waves on the distributions of atmospheric trace gases is mainly through the nonlinear photochemical reactions in the mesopause region. The contribution of the nonlinear photochemical reaction caused by gravity waves can exceed the nonlinear transportation and the eddy diffusion.