TY - JOUR
T1 - Diurnal cycle of precipitation observed in the western coastal area of Sumatra Island
T2 - Offshore preconditioning by gravity waves
AU - Yokoi, Satoru
AU - Mori, Shuichi
AU - Katsumata, Masaki
AU - Geng, Biao
AU - Yasunaga, Kazuaki
AU - Syamsudin, Fadli
AU - Nurhayati,
AU - Yoneyama, Kunio
N1 - Publisher Copyright:
© 2017 American Meteorological Society.
PY - 2017/9/1
Y1 - 2017/9/1
N2 - This study analyzes data obtained by intensive observation during a pilot field campaign of the Years of the Maritime Continent Project (Pre-YMC) to investigate the diurnal cycle of precipitation in the western coastal area of Sumatra Island. The diurnal cycle during the campaign period (November-December 2015) is found to have a number of similaritieswith statistical behavior of the diurnal cycle as revealed by previous studies, such as afternoon precipitation over land, nighttime offshore migration of the precipitation zone, and dependency on Madden-Julian oscillation (MJO) phase. Composite analyses of radiosonde soundings from the Research Vessel (R/V) Mirai, deployed about 50 km off the coast, demonstrate that the lower free troposphere starts cooling in late afternoon (a couple of hours earlier than the cooling in the boundary layer), making the lower troposphere more unstable just before precipitation starts to increase. As the nighttime offshore precipitation tends to bemore vigorous on days when the cooling in the lower free troposphere is larger, it is possible that the destabilization due to the cooling contributes to the offshore migration of the precipitation zone via enhancement of convective activity. Comparison of potential temperature and water vapor mixing ratio tendencies suggests that this cooling is substantially due to vertical advection by an ascent motion, which is possibly a component of shallow gravity waves. These results support the idea that gravity waves emanating from convective systems over land play a significant role in the offshore migration of the precipitation zone.
AB - This study analyzes data obtained by intensive observation during a pilot field campaign of the Years of the Maritime Continent Project (Pre-YMC) to investigate the diurnal cycle of precipitation in the western coastal area of Sumatra Island. The diurnal cycle during the campaign period (November-December 2015) is found to have a number of similaritieswith statistical behavior of the diurnal cycle as revealed by previous studies, such as afternoon precipitation over land, nighttime offshore migration of the precipitation zone, and dependency on Madden-Julian oscillation (MJO) phase. Composite analyses of radiosonde soundings from the Research Vessel (R/V) Mirai, deployed about 50 km off the coast, demonstrate that the lower free troposphere starts cooling in late afternoon (a couple of hours earlier than the cooling in the boundary layer), making the lower troposphere more unstable just before precipitation starts to increase. As the nighttime offshore precipitation tends to bemore vigorous on days when the cooling in the lower free troposphere is larger, it is possible that the destabilization due to the cooling contributes to the offshore migration of the precipitation zone via enhancement of convective activity. Comparison of potential temperature and water vapor mixing ratio tendencies suggests that this cooling is substantially due to vertical advection by an ascent motion, which is possibly a component of shallow gravity waves. These results support the idea that gravity waves emanating from convective systems over land play a significant role in the offshore migration of the precipitation zone.
UR - http://www.scopus.com/inward/record.url?scp=85028940992&partnerID=8YFLogxK
U2 - 10.1175/MWR-D-16-0468.1
DO - 10.1175/MWR-D-16-0468.1
M3 - 学術論文
AN - SCOPUS:85028940992
SN - 0027-0644
VL - 145
SP - 3745
EP - 3761
JO - Monthly Weather Review
JF - Monthly Weather Review
IS - 9
ER -