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Proceedings with Extended Abstracts (single PDF file) - Radio ...

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interpolation from the original grid points of the model to give conditions over the radar.These RUC data were averaged in height intervals of 0.5 km, in order to match the verticalresolution of the VHF winds. In addition, the VHF data were averaged in time, in order tomatch the 1h temporal resolution of the RUC data. Fig. 3. presents the results of thiscomparison.Fig. 3. VHF and RUC comparisons. Left: Wind direction. Right: Wind speed. Upper: scatterplot of RUC winds vs. VHF winds. Bottom: Wind difference as a function of height.3. Vortical motions.Due to the geographical location of this VHF radar, the sampling of the upper-troposphere,mid-latitude jet stream is quite frequent. Strong vortical motions have been observed duringthese events, and wind directions can often rotate by a full 360 degrees in only a few hours.Such structures can be quite deep, extending several kilometers up in the troposphere.The observations on November 23 rd , 2002, near 6 UTC, are an example of these vorticalmotions. A significant bearing of the wind can be observed through all the troposphere andthe lower stratosphere (Figure 4). This particular situation is associated <strong>with</strong> the passage of afront over the site, as well as an upper tropospheric trough embedded into the jet stream.Although not shown here, this was confirmed by operational analyses from the CanadianMeteorological Centre (CMC-MSC).In addition, comparisons between the vertical pro<strong>file</strong> of winds measured by our VHF radarand computed by the CMC-MSC operational model (i.e., GEM regional, zero hour forecast)were analyzed (not presented here). It is found that the good agreement is lost during theoccurrence of the vortical motion. This suggests the opportunity for data assimilation of VHFwind observations into numerical meteorological models.417

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