Winter Thermospheric Weather Study

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The upper atmosphere above about 85 km altitude is called the Thermosphere, because it is much hotter than the Mesosphere below, with temperatures ranging from about 500K at night at minimum solar activity to about 2000K for daytime maximum solar activity. This can be contrasted with Mesospheric temperatures in the range 150 to 200K. The high Thermospheric temperatures arise from several sources; the absorption of solar UV and X-rays during the day; the heating due to particle precipitation and electric fields associated with auroral activity; and the dissipation of the energy from gravity waves and tides that propagates up from the lower atmosphere. Measurements of the temperature of the thermosphere are made by optical interferometers and incoherent scatter radars, and latitudinal profiles are now available from a chain of four sites extending from the equator (Jicamarca in Peru) to Greenland (Sondestrom). During a January 1986 campaign anomalously low temperatures were observed at Arecibo (Puerto Rico), in comparison with results for the other sites, and it has been theorized that tides (or the absence thereof) are the cause. This award is to perform numerical modelling using the facilities of Millstone Hill Observatory to test the hypothesis.