An explosive cyclone that took place over the Northwestern Pacific from 12 UTC 18 to 18 UTC 21 November 2007 was investigated.The synoptic situations and structure of this cyclone were documented by using the 1°×1°final analysis data of the National Center for Environmental Prediction.This cyclone developed explosively around 18 UTC 19 and reached its maximum deepening rate(MDR,1.3 Bergeron)around 06 UTC 20 November 2007.At its MDR moment,the surface cyclone center was located in the downstream of the upper-level trough and northern entrance zone of the upper-level jet.The diagnosis using Zwack-Okossi equation suggested that cyclonic-vorticity advection and warm air advection acted to deepen this cyclone,while adiabatic cooling suppressed its development.In an investigation of this cyclone development,numerical sensitivity results obtained by using the Weather and Research Forecasting model showed that the latent heat release in the lower level had less contribution,whereas the surface sensible and latent fluxes played important roles.With a warmer ocean surface,the cyclone tended to intensify.Two topography tests were designed to examine the mountain influences on the development of this cyclone:removing a mountain and doubling the height of a mountain.Results show that the Changbai Mountains suppressed the development of the cyclone by preventing the southern moisture air from invading the inland.Without the moisture air,no latent heat release occurs when this cyclone passes over the Changbai Mountains.
SUN BaitangLI PengyuanZHANG ShuqinGUO JingtianFU Gang
Explosive cyclones(ECs)over two basins in the Northern Hemisphere(20°-90°N)from January 1979 to December2016 are investigated using ERA-Interim and Optimum Interpolation Sea Surface Temperature(OISST)data.The classical definition of an EC is modified considering not only the rapid drop of the central sea level pressure of the cyclone,but also the strong wind speed at the height of 10 m in which maximum wind speeds greater than 17.2 m s^-1are included.According to the locations of the northern Atlantic and northern Pacific,the whole Northern Hemisphere is divided into the"A region"(20°-90°N,90°W-90°E)and"P region"(20°-90°N,90°E-90°W).Over both the A and P regions,the climatological features of ECs,such as their spatial distribution,intensity,seasonal variation,interannual variation,and moving tracks,are documented.
2012年9月21日山东半岛南部海岸发生了一次局地性的极端暴雨过程,在约13h内降雨量达到394.1mm。该降雨过程不属于常规的暴雨天气形势,在高低空均没有典型的天气系统。本文利用自动气象站观测资料、雷达探测资料和0.25(°)×0.25(°)的ECMWF(European Centre for Medium-Range Weather Forecasts)再分析资料,对引发这次暴雨过程的多个影响因素进行了分析。结果显示:该天气系统并不深厚,但低空水汽辐合显著。自高层到低层大气层结呈现稳定-不稳定-稳定-不稳定的态势,利用位涡来表征的动力对流层顶出现明显的折叠现象,中高层干冷空气下滑与低层暖湿气流混合产生凝结可能是产生此次强降水的主要原因。湿位涡(MPV)的2个分量MPV1和MPV2的变化均发生在降雨前,MPV2在低层对降雨落区具有较好的示踪效果。中低层的等位温面上具有较强的向东位涡平流,风向与等位涡线几乎垂直,说明本次过程移动较快。
In this paper,we use FNL grid data obtained from the National Centers for Environmental Prediction(NCEP)to analyze an explosive cyclone(EC)that occurred over the northwestern Pacific Ocean from January 11 to 13,2012.To simulate the EC,we used the Weather Research and Forecasting model(WRFV3.5).The cyclone outbreak occurred east of Japan from January 11 to 12 and weakened near the Kamchatka Peninsula on January 13.The analysis results show a distinct frontal structure,in which the high potential vorticity(PV)of the upper troposphere extends downward to the surface,which can facilitate EC development.A low-level jet stream develops with the EC,which can lead to more distinct convergence.The results of sea surface temperature(SST)sensitivity tests suggest that changes in the SST can affect cyclone intensity,but have little effect on its path.When small changes are made to the SST,the air pressure at the cyclonic center responds more distinctly to an increased SST than a decreased SST.The results of our latent heat release test suggest that diabatic heating processes lead to maximum PV values in the lower troposphere.Latent heat is also one of the important factors influencing EC development.
The synoptic situation and mesoscale structure of an explosive extratropical cyclone over the Northwestern Pacific in March 2007 are investigated through weather station observations and data reanalysis. The cyclone is located beneath the poleward side of the exit of a 200 hPa jet, which is a strong divergent region aloft. At mid-level, the cyclone lies on the downstream side of a well-developed trough, where a strong ascending motion frequently occurs. Cross-section analyses with weather station data show that the cyclone has a warm and moist core. A ‘nose' of the cold front, which is characterized by a low-level protruding structure in the equivalent potential temperature field, forms when the cyclone moves offshore. This ‘nose' structure is hypothesized to have been caused by the heating effect of the Kuroshio Current. Two low-level jet streams are also identified on the western and eastern sides of the cold front. The western jet conveys cold and dry air at 800–900 hPa. The wind in the northern part is northeasterly, and the wind in the southern part is northwesterly. By contrast, the eastern jet carries warm and moist air into the cyclone system, ascending northward from 900 hPa to 600–700 hPa. The southern part is dominated by the southerly wind, and the wind in the northern part is southwesterly. The eastern and western jets significantly increase the air temperature and moisture contrast in the vicinity of the cold front. This increase could play an important role in improving the rapid cyclogenesis process.
Spatial distribution and seasonal variation of explosive cyclones （ECs） over the North Atlantic from October 2000 to September 2016 are investigated using the reanalysis data of Final Analysis （FNL）, Mean Sea Level Pressure （MSLP） and Optimum Interpolation （OI） Sea Surface Temperature （SST） provided by the National Centers for Environmental Prediction （NCEP）, the European Centre for Medium-Range Weather Forecasts （ECMWF） and the National Oceanic and Atmospheric Administration （NOAA）, respectively. Considering the meridional distribution of ECs and 10-m height wind field associated with the ECs, the definition of EC given by Yoshida and Asuma （2004） is modified. It is found that the ECs occurred mainly in four regions during winter season, namely, North America continent （NAC）, the Northwest Atlantic （NWA）, the North-centzal Atlantic （NCA）, and the Northeast Atlantic （NEA）, depending on the spatial distribution of EC＇s maximum deepening rate of central sea level pressure （SLP）. According to the magnitude of maximum deepening rate, the trend of EC numbers basically decrease with the increase of EC＇s maximum deepening rate over the North Atlantic during the whole time period. Over the North Atlantic basin, for monthly statistics, the NEA, NCA, and NWA cyclones occur mainly in December, from December to March, and from January to February, respectively. NWA, NCA and NEA cyclones in winter are associated with low-level barocliincity, both low-level baroclinicity and upper-level forcing and upper-level forcing, respectively. According to monthly variation, the averaged maximum deepening rate of central SLP firstly increases and then decreases from July to June. Overall, the distribution of ECs＇ tracks is basically in the southwest-northeast direction. During winter circulation stage （from October to May）, the averaged maximum deepening rate of central SLP and the averaged minimum central SLP of ECs decrease, and the averaged explosive-deepening duration
利用美国国家环境预报中心(NCEP,National Centers for Environmental Prediction)提供的FNL(Final Analysis)格点资料和CIMSS(Cooperative Institute for Meteorological Satellite Studies)提供的红外云图,对2014年3月25—28日发生在大西洋上的一个爆发性气旋进行了研究。分析了该气旋的移动路径和中心气压的变化,并对其演变过程中的天气形势和爆发过程中的气旋中心特征进行了分析。该爆发性气旋在2014年3月25日受美国东南部上空的槽影响而生成,之后两天在北美洲东部沿岸向东北方向移动的过程中快速发展,于28日在加拿大东南部的海面上空衰亡。分析发现,气旋中心气压降低率不断升高的过程中,气旋西部一直有相当强的冷平流输送,同时相对湿度较大,较强的潜热加热、高位涡能量下传可能是气旋发生爆发性发展的原因。
