DWM07: A global empirical model of upper thermospheric storm-induced disturbance winds
We present a global empirical disturbance wind model (DWM07) that represents average geospace-storm- induced perturbations of upper thermospheric (200-600 km altitude) neutral winds. DWM07 depends on three parameters: magnetic latitude, magnetic local time, and the 3-hour Kp geomagnetic activity index. The latitude and local time dependences are represented by vector spherical harmonic functions (up to degree 10 in latitude and order 3 in local time), and the Kp dependence is represented by quadratic B splines. DWM07 is the storm time thermospheric component of the provisional Horizontal Wind Model (HWM07) and is based on data from the Wind Imaging Interferometer (WINDII) on board the Upper Atmosphere Research Satellite (UARS), the Wind and Temperature Spectrometer (WATS) on board Dynamics Explorer 2 (DE 2), and seven ground-based Fabry-Perot interferometers (FPIs). The perturbation winds derived from the three data sets are in good mutual agreement under most conditions, and the model captures most of the climatological variations evident in the data.
Observations of Thermospheric Winds at Middle Latitude During the Current Solar Minimum
We summarize observations of winds in the lower and upper thermosphere by the Millstone Hill incoherent scatter radar (42.6N, 288.5E) during the current solar minimum and compare them with the previous results at the same location. The core dataset consists of two 30-day campaigns in September 2005 and March 2006 as well as by-weekly experiments from March 2007 to April 2008 in support of IPY/IHY program. In the lower thermosphere, the most pronounced feature is a sustained increase in the amplitude of semidiurnal tide in both zonal and meridional wind components. At the F-region heights, strong equatorward winds are observed during nighttime. We discuss relative importance of high latitude heat sources, EUV and electron density on the observed circulation.
Assessing the validity of the approaches to extracting secular trends in number density due to global warming
Numerous studies on deducing the secular trends associated with climate change have indicated that global warming leads to a decrease in neutral density in the upper atmosphere. However, different studies found rather different decreasing trends ranging from 7% per decade to 4% per decade. Evidently, data analysis plays an important role in obtaining the results. Here we wish to re-examine the approaches adopted in previous studies that were used to deduce the trends. We have conducted a few tests to see if the approaches and the assumptions used in the previous studies were physically sound. Our study indicates that we need to be cautious about the approaches we use for data analyses and the interpretations therefrom.