Liu X.,Meteorological science Institute of Jiangxi Province |
Liu X.,CAS Institute of Atmospheric Physics |
Liu X.,Chinese Academy of Meteorological Sciences |
Cheng X.,CAS Institute of Atmospheric Physics |
And 5 more authors.
Advances in Atmospheric Sciences | Year: 2013
In southern China, cold air is a common weather process during the winter season; it can cause strong wind, sharp temperature decreases, and even the snow or freezing rain events. However, the features of the atmospheric boundary layer during cold air passage are not clearly understood due to the lack of comprehensive observation data, especially regarding turbulence. In this study, four-layer gradient meteorological observation data and one-layer, 10-Hz ultrasonic anemometer-thermometer monitoring data from the northern side of Poyang Lake were employed to study the main features of the surface boundary layer during a strong cold-air passage over southern China. The results show that, with the passage of a cold air front, the wind speed exhibits low-frequency variations and that the wind systematically descends. During the strong wind period, the wind speed increases with height in the surface layer. Regular gust packets are superimposed on the basic strong wind flow. Before the passage of cold air, the wind gusts exhibit a coherent structure. The wind and turbulent momentum fluxes are small, although the gusty wind momentum flux is slightly larger than the turbulent momentum flux. However, during the invasion of cold air, both the gusty wind and turbulent momentum fluxes increase rapidly with wind speed, and the turbulent momentum flux is larger than the gusty wind momentum flux during the strong wind period. After the cold air invasion, this structure almost disappears. © 2012 Chinese National Committee for International Association of Meteorology and Atmospheric Sciences, Institute of Atmospheric Physics, Science Press and Springer-Verlag Berlin Heidelberg.
Fu M.-N.,Nanjing University of Information Science and Technology |
Fu M.-N.,Meteorological science Institute of Jiangxi Province |
Zou H.-B.,Meteorological science Institute of Jiangxi Province |
Zou H.-B.,Sun Yat Sen University |
And 4 more authors.
Journal of Tropical Meteorology | Year: 2013
A quantitative diagnosis is carried out for the upward branch of a local meridional circulation over southern China (SC) during the abnormal snowstorms with severe freezing rain from 10 January to 3 February 2008. The diagnostic study shows that the upward branch is mainly associated with the zonal advection of westerly momentum and meridional temperature advection instead of the latent heating (which is commonly the dominant factor in many other storm cases). The corresponding weather analyses indicate that (1) the zonal advection of westerly momentum represents the effect of the upper-level divergence on the anticyclone-shear side in the entrance of a 200 hPa westerly jet with a westward deviation from its climatological location over southwestern Japan; (2) the meridional temperature advection represents the interaction between the mid-lower layer (850 to 400 hPa) warm advection over SC (ahead of temperature and pressure troughs with the latter trough deeper than the former in the Bay of Bengal) and cold advection over north China (steered by an underlying flow at 500 hPa); (3) the relatively weak vapor transport (compared to that of spring, summer and autumn) from the Bay of Bengal and the South China Sea to SC and the existence of a temperature inversion layer in the lower troposphere over SC diminish the effect of latent heating. With the significant increase of vapor transport after 24 January, the role of latent heating is upgraded to become the third positive contributor to the upward branch over SC.
Liu Y.,CAS Qingdao Institute of Oceanology |
Huang H.,CAS Qingdao Institute of Oceanology |
Qiu Z.,Nanjing University of Information Science and Technology |
Fan J.,Meteorological Science Institute of Jiangxi Province
International Journal of Applied Earth Observation and Geoinformation | Year: 2013
Beach heights and tidal variation have large impacts on the accuracy of estimates ofcoastline position and its historical changes of a wider and flatter beach based on remote sensing data. This study presents an approach to analysis of waterline movement based on the beach slope, estimated from two effective images with Landsat images data. Two images acquired at different stages of the tide were processed to delineate accurately the position of the waterline. Then waterlines were assigned heights using elevations predictedby a two-dimensional non-linear tidal assimilation model. Beach slope can be calculated piecewise using the heighted shorelines based on the equiangular triangle theory. The positions of the national tidal height datum coastline can be obtained by the beach slope calculation method to accurately monitor the changing of coastline. A change in the coastline of the southwest tidal flat of the Yellow River delta, from Tianshuigou to the XiaoqingRiver mouth, was detected by combining field measurements of profiles and bathymetric data. The root mean squared error (RMSE) of the calculated slope of the intertidal zone was one order of magnitude less than the measured slope. The minimum error of self-consistency check is 0.2%. The RMSE between the coastlines estimated by the proposed method and those surveyed data varies from 53.98 m to 217.72 m. It is shown that this method is more suitable for the two years and over the time scales of shoreline change monitoring. To assess erosion/accretion patterns in the tidal flat, and the controlling factors, the volume of the beach was investigated as a possible indicator. The accepted coastline position and changes in the beach volume were used to monitor the changing pattern of accretion and erosion along the coast southwest of the recent Yellow River mouth. © 2012 Elsevier B.V.