| Cold vortex in Northeastern China(NECV), a kind of cut-off low on upper level prevailing in the mid-high latitudes of East Asia, is an synoptic scale system persisting 3 to 5 days.The frequence of NECV effected the climate in Northeast Asia especially in eastern China significantly. In consequence, “Climate Effect”of NECV was given and researched by Chinese scholars in early 21 st century, which enriched the theoretical study of NECV.Blocking high was the primary point in theoretical research on blocking pattern in the mid-high latitudes of the Northern Hemisphere in the past. Using the NCEP/NCAR daily reanalysis data from 1948 to 2012 and the observations data of precipitation in China from 1960 to 2012, the study started from the abnormal activity of NECV. Firstly, based on quantitative method of automatic recognition by machine which revealed the characters on synoptic and climatic scale of NECV, “Climate Effect”of NECV was enriched and the research of monthly precipitation prediction in Northeast China based on vortex indexhad been done. Secondly, applying the same approach, the activity of blocking high in Asia have been retrieved quantitatively.The study of the configuration between NECV and blocking high had been done. The research focused on the mechanism of interaction, formation, evolution and extinction between blocking pattern in high latitudes(Mainly Ural Mountain-Okhotsk double blocking pattern) and NECV. The results are as follows:(1) NECV activity process was provided during May to Aug from 1948 to 2012, the NECV process occurs 956 times in total, the average annual occurred about 14.7 times in May-August. And the NECV events were 4129 days, a total of 64 days accounted for 52% of the total number of days, respectively 14、18、18 and 14 days in May to August. The NECV process main sustained 3-6 days, maintaining position in the 121oE-131 oE and 48oN-53 oN. Simultaneously, the NECV frequency of occurrence and active days significant increases.In July-August the strong NECV year, Lake Baikal to the Sea ofOkhotsk blocking high regularly was simultaneous with the NECV. On the contrary, in the weak NECV year, Lake Baikal to the Sea of Okhotsk blocking high was not prevailed, and most year the NECV happened after the blocking high.The differences in geopotential height anomaly distribution between the strong NECV year and the weak NECV year appeared anti-phase distribution, moreover this feature in the middle(500hPa) and senior(200hPa) convection showed a nearly hemispherical scale wave train distribution. However their composite differences in geopotential height are similarity, showed a significant north-south "+,-" wave train(exceed 99% confidence level), this wave train are located in the Pacific Northwest region and the Sea of Okhotsk to the Bering Sea region, corresponding to the senior convection cyclonic and anticyclonic circulation.(2) After combining the characteristic of NECV active process, A process standard of NECV persistent activities is provided, and quantitative analysis has been done by using the NECV intensity index which has great significance on representation of NECV persistent activities. If the active of NECV is stronger, the activity of the blocking situation over the Ural Mountains and Lake Baikal in May, blocking situation over the Okhotsk Sea in Jun and Ural Mountain-Okhotsk double blocking is more obvious, blocking pattern in the mid-high latitudes is weak in Jul. Especially in Jun, the cold vortex system converge in middle to upper troposphere, which has a deep, cold structure, existing a strong baroclinic component. There was cold center in upper troposphere and thermal trough in lower troposphere. In middle to upper troposphere, westerlies have obvious shunt and confluent, and the blocking situation between them shows higher in northeast and lower in southwest. The weak year is that the NECV converge in middle to lower troposphere, and the cold center is shallow and the cold structure is not obvious, with blocking in-existence.(3) Based on the geographical distribution of cold vortex, a new method of the vortex consistence called generalized “cold vortex” by continuous anomaly of circulation is defined. In addition, the generalized “cold vortex” strengthen index, which described the activity of generalized “cold vortex” well by quantitative analyses, was given. Used this index, the activity routines of the cold vortex, characteristic of atmospheric circulation, and their effects on precipitation in Northeast China were analyzed. The activities of the cold vortex exhibit remarkable features of annual and interdecadal oscillation, and the vortex high frequency and its character of atmospheric circulation are described more accurately by the index, which showed a high correspondence with the vortex precipitation during early summer(May-Jun) and midsummer(Jul-Aug) in the northeast. In strong(weak) vortex years, the general circulation in the middle and high latitudes of Eurasia is to the advantage(disadvantage) of the formation, development and maintenance of the cold vortex, thus it is easy(difficult) to form the circulation which is beneficial to transmit vapor from south to north during the period of July to August. Ural Mountains blocking prevails(does not prevail) in early summer, and Okhotsk blocking prevails(does not prevail) in midsummer, areas where the subtropical high is too small(large) and moves toward the north too late(early) are better(worse) for the maintenance of the cold vortex in Northeastern China.(4) The period of cold vortex accounts 62.5% for the total rainfall in Northeast China from May to June. The cold vortex monthly rainfall intensity index has a good consistency with the inter-annual variability of monthly rainfall in the same period. Early summer precipitation in Northeast China is similar to the main mode of EOF decomposition of cold vortex precipitation, showing four modes as the commonly more precipitation in whole district, more precipitation in northeast and less precipitation in southwest boundary with Northeast China Plain, less precipitation in northeast and more precipitation in southwest, the commonly less precipitation in whole district. The conception of “Cumulative Effect” of cold vortex precipitation(CECEP) was characterized. The CECEP can reflect the characteristics of the spatial distribution of the summer precipitation anomaly in Northeast China in genial, and can also further reveal the climatology characteristics of cold vortex activity.(5) On account of cold vortex factors portrayed on multi-view and monthly precipitation in Northeast China during May-Aug, on the one hand, monthly precipitation prediction was studied in total 3 years from 2012 to 2014 in the region, on the other hand, precipitation return forecasting for 10 years in 2003-2012 has been examined by bringing the index into FODAS precipitation prediction system. The effect of precipitation prediction was better, which reflected the characters of spatial and temporal distribution of observation and the distribution of the amount of precipitation. The return forecasting of FODAS had a better result, which can be positive corrected steadily with most of results by index corrected being better than system corrected. The above research, which described the different character of cold vortex index depicting the vortex character in the prediction of precipitation in Northeast China, provided quantitative index product, and offered theoretical and technical support for monthly precipitation prediction in Northeast China further.(6) The blocking systems from upstream and downstream affects NECV significantly, which are in favor of NECV maintenance and strengthening. There is different influence for different region of blocking high to position and intensity of NECV, so various configurations would lead to distinctly different precipitation area of NECV. The configuration of NECV with different blocking has positive impact on precipitation in Northeastern China, such as the coexistence of Okhotsk blocking with NECV is more beneficial to precipitation. If the NECV activity is more strong(weak), the subtropical ridge is more southerly(northerly) and the westerly index is more strong(weak).Ural Mountain blocking and Okhotsk blocking prevailed in the years of more NECV activity processes; the double blocking pattern is to the benefit of the maintenance and evolution of NECV. It shows that a significantly abrupt change of Ural Mountain-Okhotsk double blocking happened at around 1977, thereafter the blocking activity’s frequency and the number of days decrease dramatically. Before(after) the abrupt change, the Ural Mountain-Okhotsk blocking high activity presented positive(negative) phase to change. The climate characteristics of double-blocking activity indicate Ural Mountain-Okhotsk blocking strengthens after the abrupt change, this typical case of double-blocking high has a characteristic that is abnormally stronger. The energy of double-blocking high mainly propagates from low to high level, energy from Ural MountainOkhotsk mainly transfers from low to high latitude instead of that previously from high to low latitude, it provides energy for the development of low pressure system between the two blocking, namely the double-blocking activity is conductive to the maintenance and development of NECV. |
PDF Full Text Request