New results on the midnight temperature maximum with the NATION Fabry-Perot network for the central eastern continental US
Thursday, 18 December 2014
We have analyzed ~300 nights of 630-nm Fabry-Perot interferometer (FPI) thermospheric temperature and wind measurements obtained by the North American Thermospheric Ionospheric Observing Network (NATION) acquired from 2010 to the present. We have examined these results to search for evidence regarding the appearance of the midnight temperature maximum (MTM) within the latitudinal range spanning from 33.1 N to 44.4 N, located in the central eastern continental US. The MTM is regarded to be the result of the blending of the upward propagating diurnal, semi-diurnal, and other higher order tidal modes and presents itself in intensities and temperatures as a poleward traveling feature with a slight eastward motion. The MSIS-00 model is used as a reference to determine the MTM amplitude for these nights. The statistical analysis of these results shows the detection of the MTM structure with an amplitude greater than or equal to 50 K to occur for ~25% of the nights, with a greater probability for summer periods. The observed MTM amplitude varies from a few tens of degrees to 250 K, maximum. Not only is variability in the local time of the MTM peak seen from one site to another, but a spatial variation of the MTM amplitude is also observed within the NATION latitude coverage. We suggest that this variability is a result of the tidal wave forcing mechanism changing from site to site due to the spatial variation of tidal wave dissipation caused by the latitudinal variation in the E- and F-region plasma densities. The additional measurements of intensities provide further insight into the MTM phenomenology with corresponding enhancements seen where there are temperature maxima. These results illustrate the advantages provided by a network of FPI observatories to help understand large-scale neutral atmosphere dynamical behavior.