Comparative Analysis of Two Freezing Disasters in Southeastern Guizhou

[Objective] The aim was to compare two freezing disasters in January 2008 and 2011 in southeastern Guizhou. [Method] By means of meteorological data from automatic stations in southeastern Guizhou, the occurrence time, influence range and disaster intensity of freezing disaste from December 31st, 2010 to January 10th, 2011 were analyzed and compared with freezing disaster in January 2008. [Result] Freezing weather in January 2011 started early and strongly, with large influence rang, lower decrease and intermittent rising of temperature, and subsequent cold air was weak, so freezing disaster weakened gradually; in January 2008, freezing weather began later and lasted for a long time, and subsequent cold air strengthened gradually, while temperature went down gradually accompanying continuous rainfall (snowfall), so freezing disaster became more and more serious. In a word, freezing disaster in January 2008 was severer than that of 2011. [Conclusion] The study could provide scientific references for the prediction and early warning of freezing disaster and establishment of corresponding countermeasures.

The Unprecedented Freezing Disaster in January 2008 in Southern China and Its Possible Association with the Global Warming

The unprecedented disaster of low temperature and persistent rain, snow, and ice storms, causing widespread freezing in the Yangtze River Basin and southern China in January 2008, is not a local or regional event, but a part of the chain events of large-scale low temperature and snow storms in the same period in Asia. The severity and impacts of the southern China 2008 freezing disaster were the most significant among others. This disastrous event was characterized by three major features： （1） snowfall, freezing rain, and rainfall, the three forms of precipitation, coexisted with freezing rain being the dominant producer responsible for the disaster; （2） low temperature, rain and snow, and freezing rain exhibited extremely great intensity, with record-breaking measurements observed for eight meteorological variables based on the statistics made by China National Climate Center and the provincial meteorological services in the Yangtze River Basin and southern China; （3） the disastrous weathers persisted for an exceptionally long time period, unrecorded before in the meteorological observation history of China. The southern China 2008 freezing disaster may be resulted from multiple different factors that superimpose on and interlink with one another at the right time and place. Among them, the La Nina situation is a climate background that provided conducive conditions for the intrusions of cold air into southern China; the persistent anomaly of the atmospheric circulation in Eurasia is the direct cause for a succession of cold air incursions into southern China; and the northward transport of warm and moist airflows from the Bay of Bengal and South China Sea finally warranted the formation of the freezing rain and snow storms and their prolonged dominance in the southern areas of China. A preliminary discussion of a possible association of this disastrous event with the global warming is presented. This event may be viewed as a short-term regional perturbation to the global warming. There is not any possibility for this event to divert the long-term trend and the overall pattern of the global warming.

Indications of stratospheric anomalies in the freezing rain and snow disaster in South China,2008

NCEP/NCAR reanalysis data were used to characterize stratospheric temperature and water-vapor anomalies before and after the freezing rain and snow disaster of South China in 2008,and the influence of stratospheric circulation anomalies on the troposphere.Stratospheric temperature and water-vapor anomalies provided good leading indicators of this weather event.The period from December 1st 2007 to February 28th 2008 was divided into 18 pentads.During the 6th pentad,temperature decreased significantly at 10 hPa in the near-polar stratospheric region,and the decreasing trend strengthened and extended downward and southward to middle and lower latitudes.During the 14th-18th pentads,the temperature decrease reached its maximum and extended to 30°N.This coincided with the widespread freezing rain and snow event.By the end of January 2008,the temperature decrease ended in the near-polar stratospheric region,but continued in the mid-latitude area of the troposphere as the freezing rain and snow weather persisted.Similar to the temperature variations,positive anomalies of relative humidity in the stratospheric near-polar region also strengthened and extended downward and southward,coinciding with the freezing rain and snow event.Along with the significant relationship between the freezing rain and snow disaster and stratospheric circulation anomalies,the stratospheric polar vortex changed its shape in late December,intensifying and spreading downward from the top of the stratosphere and southward to the Asian continent,resulting in a deepening of the East Asian Trough and a strengthening of meridional circulation.Before the occurrence of the freezing rain and snow event,temperature and vapor increases in the stratosphere transferred downward to the troposphere,along with a stratospheric flow in the near-polar region southward to lower latitudes.