Abstract
Abstract. Simultaneous observations of the mean zonal winds at 88 km obtained by the medium-frequency (MF) radars at Kolhapur (16.8° N, 74.2° E) and Tirunelveli (8.7° N, 77.8° E) have been used to study the intraseasonal oscillation (ISO) in the MLT region. The influences of the intraseasonal variations in the lower tropospheric convective activity associated with the Madden-Julian oscillations on the latitudinal behavior of intraseasonal oscillations (ISO) of the zonal winds in the equatorial mesosphere and lower thermosphere (MLT) have been studied. The ISO activity in the lower tropospheric convective activity is examined by employing outgoing long wave radiation (OLR) as a proxy for deep convective activity occurring in the tropical lower atmosphere. The ISO activity in the zonal wind over TIR is more correlated with that in the convective activity compared to the ISO over KOL. The latitudinal and temporal variabilities of the ISO in MLT zonal winds are explained in terms of the intraseasonal variabilities in the convective activity.
Highlights
The equatorial/low latitude region is the source region of many unique atmospheric processes that couple the entire atmosphere vertically
Generated waves such as Kelvin, Rossby-gravity and gravity waves play a crucial role in driving the quasi-biennial oscillation (QBO) in the lower stratosphere and the stratospheric semi-annual oscillation (SAO) (SSAO) (Lindzen and Holton, 1968; Dunkerton, 1979, 1997; Garcia, 2000), whereas Kelvin waves and gravity waves are considered to be important for driving the mesospheric SAO (MSAO) (Hirota, 1978; Dunkerton, 1982)
Zonal winds in the equatorial mesosphere and lower thermosphere (MLT) region are characterized by long-term variations such as the annual oscillation (AO) and the semiannual oscillation (SAO) (e.g., Vincent, 1993)
Summary
The equatorial/low latitude region is the source region of many unique atmospheric processes that couple the entire atmosphere vertically. We attempt to understand the latitudinal nature of the ISO in low latitude MLT region and its relation to the intraseasonal variability of convective activity associated with the MJO in the troposphere. The outgoing long-wave radiation (OLR) data (obtained from the National Oceanic and Atmospheric Administration – National Centers for Environmental Prediction (NOAANCEP)) has been used as a proxy for deep tropical convection (Hendon and Woodberry, 1993), to study the nature of the ISO activity in the lower tropospheric convection. Very high and cold clouds (low OLR) at tropical latitudes are presumed to be associated with deep convection
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