Abstract
Abstract. The climatological behaviour of the thermospheric meridional wind above Kiruna, Sweden (67.4°N, 20.4°E) has been investigated for seasonal and solar cycle dependence using six different techniques, comprising both model and experimental sources. Model output from both the empirical Horizontal Wind Model (HWM) (Hedin et al., 1988) and the numerical Coupled Thermosphere and Ionosphere Model (CTIM) are compared to the measured behaviour at Kiruna, as a single site example. The empirical International Reference Ionosphere (IRI) model is used as input to an implementation of servo theory, to provide another climatology combining empirical input with a theoretical framework. The experimental techniques have been introduced in a companion paper in this issue and provide climatologies from direct measurements, using Fabry-Perot Interferometers (FPI), together with 2 separate techniques applied to the European Incoherent Scatter radar (EISCAT) database to derive neutral winds. One of these techniques uses the same implementation of servo theory as has been used with the IRI model. Detailed comparisons for each season and solar activity category allow for conclusions to be drawn as to the major influences on the climatological behaviour of the wind at this latitude. Comparison of the incoherent scatter radar (ISR) derived neutral winds with FPI, empirical model and numerical model winds is important to our understanding and judgement of the validity of the techniques used to derive thermospheric wind databases. The comparisons also test model performance and indicate possible reasons for differences found between the models. In turn, the conclusions point to possible improvements in their formulation. In particular it is found that the empirical models are over-reliant on mid-latitude data in their formulation, and fail to provide accurate estimates of the winds at high-latitudes. Key words. Meteorology and atmospheric dynamics (thermospheric dynamics), Ionosphere (ionosphere-atmosphere interactions, auroral ionosphere)
Highlights
The companion paper has presented an introduction to shortterm comparisons and neutral wind climatologies using Fabry-Perot Interferometers (FPI) and incoherent scatter radar (ISR) databases from several sites (Griffin et al, 2004)
The results showed that the overall mean winds in HWM87 are about 50% greater than those calculated from the European Incoherent Scatter radar (EISCAT) incoherent scatter data
The Meridional Wind Model (MWM) (Miller et al, 1997) is used in the EISCAT-MWM technique, which applies servo theory to deduce winds by using hmF2 values derived from EISCAT experiments as input to the MWM, and uses the same experimental data set as the EISCAT-ISR technique
Summary
The companion paper has presented an introduction to shortterm comparisons and neutral wind climatologies using FPI and ISR databases from several sites (Griffin et al, 2004). The authors speculate that an underestimate of the high-latitude Joule heating could be the cause of this difference between the winds derived from the radar and the winds from the coupled models, including CTIM, used in the comparison. The companion paper describes direct measurements of the meridional wind by FPI and 2 techniques applied to EISCAT radar data that derive the meridional wind from plasma parameters. The Meridional Wind Model (MWM) (Miller et al, 1997) is used in the EISCAT-MWM technique, which applies servo theory to deduce winds by using hmF2 values derived from EISCAT experiments as input to the MWM, and uses the same experimental data set as the EISCAT-ISR technique. The climatologies described extend the scope and depth of the experimental climatologies presented in the companion paper, as well as provide a critique of the success of the individual techniques
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