Tropospheric winds over Sumatra – the diurnal evolution and its variability in response to large-scale phenomena

The environment of the Maritime Continent (MC) is known to be affected by numerous interactions between local and large-scale weather modes. Here, the primary mode of variability in tropospheric winds – the diurnal cycle – is investigated based on Equatorial Atmosphere Radar (EAR) which provides powerful information about tropospheric dynamics over a wide range of altitudes, with high temporal frequency and over a long period.

The study focuses on mean profiles for the three wind components, as well as their decomposition into diurnal and semi-diurnal cycles. The mean diurnal evolution of winds during boreal winter as well as variability associated with assorted weather phenomena has been investigated. Interannual modes such as Quasi-Biennial Oscillation (QBO), ENSO and Indian Ocean Dipole (IOD) were analyzed. On subseasonal time scale, the effects of Madden-Julian Oscillations (MJO) and convectively coupled Kelvin waves (CCKW) on diurnal wind evolution were studied. All of the above-mentioned weather phenomena are known to affect precipitation patterns across the MC region. This analysis contributes to understanding of physical processes responsible for such interactions. Obtained results were compared against the ERA-5 reanalysis.

The results show a large discrepancy between the vertical wind profiles between EAR and reanalysis. The observed variability in the vertical profiles of wind components was related to the temperature profile and the occurrence of cumulus congestus clouds in the MC area. Furthermore, a substantial effect of ENSO phase, as well as MJO and CCKW on the magnitude of diurnal and semi-diurnal cycle amplitudes, was observed at all altitudes. Meanwhile, it is found that the influence of IOD is imperceptible, while QBO effects are limited to levels above 200mb. It is noteworthy that the described impacts are larger in the EAR observations than in the reanalysis data.