Typical weather station wind measurements are horizontal wind speed and direction. This two dimensional value can broken apart into one dimensional components. The typical convention is to express wind speeds in components oriented north/south and east/west. The "u" component is the east/west one dimensional speed and the "v" component is the north/south one dimensional speed. The featured chart presents the climatology of these two values (top panel) based on long term data from the Des Moines Airport weather station. The bottom panel is the simple average of the magnitude of the wind speed. This type of plot tells an interesting story about the "v" component wind. This wind is typically responsible for the warm and cold air mass transport into Iowa. The plot shows a clear annual cycle between northerly winds (negative v) during the cold season and southerly winds (positive v) during the warm half. The transition from northerly to southerly happens about this time of year! Of course, not every day during the warm season experiences southerly winds, but when you average all the data out it is southerly.

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Tags:   wind