Measurement of Momentum Fluxes near the Summer Mesopause at Poker Flat, Alaska

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Abstract
Observations of the motion field near the summer mesopause using the Poker Flat MST radar in a symmetric six-beam configuration during 8 days of July 1986 were used to examine the mean structure, the wave variances, and the momentum fluxes due to gravity wave and tidal motions. Our results reveal a mean horizontal wind structure generally consistent with previous observations, but with considerable daily variability and large mean shears. Particularly significant is a mean downward (Eulerian) vertical velocity of ∼0.3 m s−1, which implies a significant upward flux of wave energy. Horizontal and vertical velocity variances are found to be ∼1500 and 6 m2 s−2 and to remain nearly constant with height. Momentum flux measurements reveal a largely zonal mean flux of ∼5 to 15 m2 s−2 that achieves a maximum just below the height of wind reversal. Daily mean values, on the other hand, exhibit large variability, with maxima as large as ∼30 to 40 m2 s−2. Hourly momentum flux profiles were found to achieve m... Abstract Observations of the motion field near the summer mesopause using the Poker Flat MST radar in a symmetric six-beam configuration during 8 days of July 1986 were used to examine the mean structure, the wave variances, and the momentum fluxes due to gravity wave and tidal motions. Our results reveal a mean horizontal wind structure generally consistent with previous observations, but with considerable daily variability and large mean shears. Particularly significant is a mean downward (Eulerian) vertical velocity of ∼0.3 m s−1, which implies a significant upward flux of wave energy. Horizontal and vertical velocity variances are found to be ∼1500 and 6 m2 s−2 and to remain nearly constant with height. Momentum flux measurements reveal a largely zonal mean flux of ∼5 to 15 m2 s−2 that achieves a maximum just below the height of wind reversal. Daily mean values, on the other hand, exhibit large variability, with maxima as large as ∼30 to 40 m2 s−2. Hourly momentum flux profiles were found to achieve m...

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