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Abstract:
We carried out two campaign observations over the southwestern coastal land and adjacent sea of Sumatera Island, Indonesia, during November-December 2015 (pre-YMC 2015, hereafter Y15) (49 days) and November 2017-January 2018 (YMC-Sumatra 2017, hereafter Y17) (61 days). We deployed two land observation sites in Bengkulu city on the southwestern coast of Sumatra Island with various kinds of instruments including an X-band dual polarization (DP) and operational C-band Doppler radars, and the R/V Mirai over the coastal sea with a C-band DP radar. Intensive 3-hourly soundings were conducted both over the land and the vessel during both periods. Synoptic conditions during the Y15 (Y17) corresponded to El Niño (La Niña) and large scale cloud areas of active Madden-Julian Oscillation (MJO) passed over Sumatra Island in the about later (former) 10 days of the period, i.e., most of both campaign periods were convectively MJO inactive phases. Rainfall at Bengkulu during Y15 showed clear diurnal variation with active thunderstorms every day (31 days) during the Y15 until MJO active phase onset over Sumatra. Whereas rainfall diurnal variation in Y17 was quite unclear and its peak time was delayed approximately 2 hours than that in Y15 though both periods corresponded to mostly MJO inactive phases. In particular, the thunderstorm during Y17 was quite a few (9 days) and only a short time within an hour. Characteristics that brought different convective activities between two campaign periods, e.g., diurnally developed local winds, atmospheric instabilities, and spatiotemporal variations of radar echo distribution, were analyzed for further discussion.
