Study on Cold Wave Weather in Hexi Corridor from March 12 to 14 in 2011

[ Objectivel The aim was to study the cold wave in Hexi Corridor in 2011 and to summarize report experience. [ Method] Routine obser- vation data and Ecmwf numerical product were used to analyze the circulation background, causes and influential system of Hexi Corridor from March 12 to 14 in 2011. [Result] The cold wave in the mid-high latitude circulation in Northern hemisphere transited from radial type to warp type. High early basic temperature was the premise of cold wave. Drastic ground movement was the direct cause of cold wave. Prevailing cold advection was one primary cause of temperature reduction. Radiation in sunny days also posed certain influences on regional temperature. Factors weakened the gale were as follow, cold air largely in north area, cold air moving southeastward in diffusion, front passing early, upper and lower air conver- gence against the convection development and slow wind in high and lower air. [ Conclusion] The study provided important references for further enhancement of cold wave and gale report.

Analysis of a Turning Cold Wave in Northern Xinjiang in Winter

Based on analyzing the circulation development of 100 hPa, 500 hPa, lower streamline field and the change of physical vadables, the diagnostic analysis of a turning cold wave process in northern Xinjiang from Feb. 10 -13th 2009 was carried out. The results showed that abnormality of 100 hPa polar vortex taking on stable two waves, catastrophe of 500 hPa western Siberian trough, strong cold advection and water vapor transport from Middle Asia are chief reasons of the process.

Analysis on the Unstable Trigger Mechanism of A Rare Strong Convection Weather in North-central Fujian Province

By using NCEP reanalysis data,the formation reason of a disaster weather process which happened in Fujian Province on April 1,2007 was analyzed. The results showed that this strong convection weather process was caused by the development of convective thunderstorm monomer in the warm zone of jet stream which was in front of ground front at afternoon. The invasion of cold advection in the middle-high layer had the major trigger effects on this strong convection weather occurrence. The tilt development of vorticity was easy to appear in θse tilted frontal zone,which made a large amount of latent heat release exist in the middle layer of troposphere. Meanwhile,it favored the potential vorticity in the middle layer to download. Thus,it made the important contributions to the development,maintenance of low-altitude vorticity in the strong convection zone and favored the development,maintenance of thunderstorm. In the middle-low layer of troposphere where the strong convection happened,the distribution of meso-scale wave train which was similar to the gravity wave appeared. Meanwhile,it also reflected the wave characteristics which the ascending motion alternated with the descending motion in the divergence. The westerly disturbance in the middle-low layer of troposphere,the southerly disturbance in the low altitude and the middle-upper layer of troposphere made the important contributions to the strong convection weather. The easterlies disturbance and the divergence effect in the tropopause strengthened the development of vertical motion. The strong vertical wind shear was the favorable condition of strong convection weather occurrence.

Roll Vortices in the Boundary Layer Caused by a Concave Wind Profile: A Theoretical Study

The present study solves a two-layer atmospheric wave equation model with a lower atmosphere concave wind profile and cold-air outbreak over sea, while simultaneously proving that such a wind shear may cause neutral boundary layer roll vortices in the presence of disturbing sources upstream. Without thermal effects, the wind shear-induced waves have band structures at the top of the boundary layer that are similar to cloud street patterns observed over sea. This study proves that dynamic and thermal effects can act independently to initiate the roll vortices in the lower atmosphere. At the same time, a quantitative comparison shows that dynamic effects play a large role in the formation of roll vortices in the initial stage of cold-air outbreak and will be surpassed by thermal effects soon after surface heating commences.

The interaction of Hurricane Michael with an upper trough leading to intensification right up to landfall

Hurricane Michael was intensifying as it made landfall devastating areas of the Florida Panhandle including the small town of Mexico Beach.The structure of the hurricane is examined using radar wind data made available from aircraft reconnaissance missions.This showed a dominant warm air advection configuration(winds turning in direction in an anticyclonic fashion with height)around the core of the hurricane.Conventional radiosonde data was also used to study the warm air advection environment east of a deep layered tough system which Michael moved into and which appeared to favour such strong intensification.The structure of this deep trough is also examined and compared with a situation where Hurricane Dennis in 2005 weakened as it approached the coast in much the same region.It appears that the thermal structure of the upper trough at low to middle levels is critical to whether the hurricane intensifies or weakens with the presence of strong cold air advection associated with weakening.