Abstract
Abstract. The meteor trail echo decay rates are analysed on-site to provide daily temperatures near 90 km. In order to get temperatures from trail decay times, either knowledge of the pressure or the background temperature height gradient near 90 km is required (Hocking, 1999). Hocking et al. (2004) have developed an empirical 90 km temperature gradient model depending only on latitude and time of year, which is used in the SKiYMET on-site meteor temperature analysis. Here we look at the sensitivity of the resulting temperature to the assumed gradient and compare it and the temperatures with daily AuraMLS averages near Eureka. Generally there is good agreement between radar and satellite for winter temperatures and their short-term variations. However there is a major difference in mid-summer both in the temperatures and the gradients. Increased turbulence in summer, which may overwhelm the ambipolar diffusion even at 90 km, is likely a major factor. These differences are investigated by generating ambipolar-controlled decay times from satellite pressure and temperature data at a range of heights and comparing with radar measurements. Our study suggests it may be possible to use these data to estimate eddy diffusion coefficients at heights below 90 km. Finally the simple temperature analysis (using satellite pressures), and a standard meteor wind analysis are used to compare mean diurnal variations of temperature (T) with those of zonal wind (U) and meridional wind (V) in composite multi-year monthly intervals.
Highlights
Discussions of the pressure or the background temperature height gradient near 90 km is required (Hocking, 1999)
Hocking et The Eureka meteor radar (MR) has been operating since agwalnr.haaid(lcy2ihes0ni0ists4.m)usohedadveleinddetephveeenlSdoKipneigYdoMannElyTeomonpnli-arsiticittaeuldm9e0eatkenmodrtittomeemmfepptoeehCfrraayeltteiuumarrPree, aatsetFi2rna0edb1caor1rul)lt.aaerTbmyohp2reea0rtp0iaro6teun.srSeweonsimt.thpeatwhpeeinrSdivsdaalobtuaarrhdfiarvMsetRalol(roMeokaafdanyttshCboEDenueilesriencemtPukpasaualsa.bim,otsl2neies0stthe0eo9dr, Here we look at the sensitivity of the resulting temperature
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Summary
Temperature and geopotential height (GPH) data are available from the MLS. The “EOS MLS Version 2.2 Level 2 data quality document and description document” (JPL D-33509) gives vertical resolution for temperature as 14 km, and for geopotential height, 700 m, near 0.001 hPa (∼ 90 km GPH). All the suggested selection criteria are applied except for the occasional stated use of one, or sometimes two, levels above the recommended upper limit of 0.001 hPa. Data from latitude bin 79.9◦ N and longitudes within one-half of the satellite track spacing (about 230 km) from Eureka are included in the analysis. Geopotential height and temperature data files are combined, along with the MLS fixed pressure level grid, in order to interpolate the temperatures, their gradients, and pressure parameter log P to GPH levels, e.g. 90 km. For present offline use in this paper, we have very simple rules: for decay times, non-ambiguous echo location 0.0150 s < τ1/2 < 2 s, and additional criteria for wind analysis, zenith angle between 10 and 70◦ and relative error in Doppler velocity σVr /Vr < 0.25
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