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Daytona Beach


Physical Sciences

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Using meteor radar, radiosonde and digisonde observations and MERRA-2 reanalysis data from 12 August to 31 October 2006, we report a dynamical coupling from the tropical lower atmosphere to the mesosphere and ionospheric F2 region through a quasi 27-day intraseasonal oscillation (ISO). It is interesting that the quasi 27-day ISO is active in the troposphere and stratopause and mesopause regions, exhibiting a three-layer structure. In the mesosphere and lower thermosphere (MLT), the amplitude in the zonal wind increases from about 4 ms at 90 km to 15 ms at 100 km, which is different from previous observations that ISOs generally have the amplitude peak at about 80-85 km, and then weakens with height. OLR and specific humidity data demonstrate that there is a quasi 27-day periodicity in convective activity in the tropics, which causes the ISO of the zonal wind and gravity wave (GW) activity in the troposphere. GW energy in the stratosphere also exhibits a sharp spectral speak at 27-day period, meaning that the convectively modulated GWs play a vital role in driving the oscillation in the MLT. The quasi 27-day variability arises clearly in the hmF2. Wavelet analysis shows that the dominant period and active time of the hmF2 oscillation are in good agreement with those in the zonal wind of the MLT and OLR rather than in the F10.7 and Kp index. Hence, tropical convective activity has an influence on the dynamics of the MLT and F2 region through modulated waves and ISOs.




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