Analysis on the Climate Variation Characteristics of Frost in Shandong Province

[Objective] The research aimed to study the climate variation characteristics of frost in Shandong Province. [Method] The daily minimum surface temperature ≤ 0 ℃ in autumn or spring was as the frost index. Based on the daily minimum surface temperature data in 67 meteorological observatories of Shandong Province during 1961-2008, the variation characteristics of first, last frost dates and frost-free period in Shandong Province were analyzed by using the climate diagnosis analysis method. [Result] The climate characteristics of first, last frost dates and frost-free period had the obvious geographical differences in Shandong Province in recent 48 years. The extreme differences of first, last frost dates and frost-free period were all above the three times of their standard deviations. It illustrated that the dispersion degrees of first, last dates and frost-free period were all very big. The average first frost date postponed with 1.99 d/10 a velocity in Shandong Province in recent 48 years, and the last frost date advanced with 1.46 d/10 a velocity. The postponing range of first frost date was bigger than the advancing range of last frost date, and the frost-free period prolonged with 3.42 d/10 a velocity. Seen from the interdecadal variations, the first frost date started to obviously postpone, and the last frost date obviously advanced since the 1990s. The frost-free period also started to obviously prolong since the 1990s. [Conclusion] The research provided the certain reference for the predication, prevention of frost disaster and the structure adjustment of crops.

STUDY ON THE MAIN CLIMATE MODES OF SHANDONG PRECIPITATION AND THEIR RELATIONS WITH THE EAST ASIAN WESTERLY JET

Summer precipitation patterns of Shandong Province are relatively independent with regard to the whole eastern China region.To study the rules and causes of precipitation variations,three main climate modes-on the annual,seasonal,and climatic intra-seasonal oscillation(CISO) scales-are extracted using a harmonic analysis method based on daily precipitation of Shandong during 1965-2009 and multi-year averaged pentad precipitation at 722 stations in China during 1971-2000.Among the three precipitation climate modes,the annual mode is closely related to the annual cycle of Earth-Atmosphere thermal system,which is characterized by the periodic dry and wet seasons.The seasonal mode reflects the monsoon effect on precipitation and the main flood season's contribution to annual precipitation variations.As an important climatic signal,the CISO mode is more evident during summer monsoon.The gradual modulations of the CISO mode,seasonal mode,and annual mode control the annual variation of precipitation.To study the relationship between precipitation climate modes and atmospheric circulations,an East Asian Westerly Jet Index(EAWJI) is defined in this paper.It is revealed that precipitation of Shandong is closely related to EAWJI in all climate modes.A wet or dry phase of each climate mode corresponds to a specific atmospheric circulation pattern.The phase of the annual mode is reverse to that of EAWJI.During the wet phase of the seasonal mode(weak phase of EAWJI),the atmospheric circulation in and around Shandong is characterized by upper-level divergence and low-level convergence.A reversed atmospheric circulation exists for the dry phase(strong phase for EAWJI).In the summer wet phase of CISO mode(strong phase of EAWJI),Shandong is controlled by upper-level divergence and low-level convergence.Again,the dry phase is corresponding to a reversed circulation structure.The methodology employed in this research,i.e.studying the precipitation climatic variations in terms of independent components of different temporal scales,provides a new approach for annual and seasonal precipitation prediction.

ANALYSIS OF TYPHOON MATSA (NO.0509) AFFECTING SHANDONG PROVINCE

The characteristics of the moving course of Typhoon Matsa (No.0509), associated heavy rain and physical quantities fields have been analyzed, with the focus on the reason of the typhoon’s abrupt northeastward turn in Anhui Province and heavy rain concentrating in the northeast of typhoon center instead of near it. Meaningful conclusions are as follows. The reasons for typhoon abrupt turning are that the subtropical high pressure was moving southward and divergence fields of 200 hPa were to the right of the typhoon center; there was no obvious cold air invading Shandong after the typhoon entered the westerly belt; the southeasterly jet of typhoon and shear brought heavy rainfall to the Shandong peninsula before the typhoon entered Shandong. But after the typhoon’s movement into Shandong, the typhoon’s inverted trough brought the rainfall to the northern and central Shandong.

PREVIOUS CONVECTION ANOMALY IN AUTUMN AND WINTER ASSOCIATED WITH THE GENERAL CIRCULATION OVER EAST ASIA IN WINTER AND SPRING AND APRIL PRECIPITATION IN SHANDONG

Using OLR and 850 hPa and 200 hPa wind fields data (1979 - 2006), this paper diagnoses the characteristics of convection over the tropical area in preceding autumns and winters in association with April precipitation anomalies in Shandong province. It is found that preceding convection anomalies over the Western Pacific Warm Pool in December have close relationships with the April precipitation in Shandong. Further analysis of the relationship with the general circulation over the East Asia shows that the convection anomaly over the Western Pacific Warm Pool has close relationships with the Main East Asian Trough, the Hadley cell over East Asia and the Walker cell. The characteristics of East Asian atmospheric circulation anomalies accompanied with stronger (weaker) convection are consistent with those of less (more) April precipitation anomalies in Shandong. Therefore, the convection anomaly over the tropics in December may be an important indicator for April precipitation in Shandong.

Analysis of a Continuative Fog Event in Western Shandong Province

[Objective] The aim was to study a continuative fog event in center and western Shandong Province from December 3 to 7 in 2011. [ Method] Based on regular meteorological data, a continuative heavy fog weather process during December 3 to 7 in 2011 was analyzed from the aspects of weather background, ground factors, T-Inp, and moisture and physical quantity field. [ Result] The heavy fog occurred under then at- mospheric circulation pattern controlled by the straight westerly air flow at 500 hPa middle latitudes, ridge of high pressure at middle and low levels, and weak pressure at the bottom of the surface high. The snowfall process for the formation of fog provided vapor conditions of fog, maintenance and development had benefited from lower layer of the warm and humid airflow. During the heavy fog, wind speed was between 1 and 3 m/s. The dew difference and visibility in the eady period had distinct daily changes, while the difference narrowed in the middle and later stage. Close to the ground was an obvious inversion layer, at the same time in the fog strong period temperature inversion layer were apparent between 700 and 800 hPa, these were helpful for fog formation and development. The stable atmospheric stratification, while low layer of weak convergence ascending motion, high level in the presence of weak divergence subsidence, these were also conducive to the maintenance and development of the fog. [ Conclusion] The study provided theoretical basis for the forecast of fog weather.

The Structure and Evolution of Sea Breezes During the Qingdao Olympics Sailing Test Event in 2006

Using data from automatic surface weather stations, buoys, lidar and Doppler, the diurnal variation and the three-dimensional structure of the sea breezes near the sailing sites of the Good Luck Beijing- 2006 Qingdao International Regatta from 18 to 31 August 2006 are analyzed. Results show that excluding rainy days and days affected by typhoon, the sea breezes occur nearly every day during this period. When Qingdao is located at the edge of the subtropical high at 500 hPa, the sea breeze is usually stronger, around 3-4 m s^-1. It starts at around 1100 to 1300 LST and lasts about 6 hours. The direction of the sea breeze tends to be southeasterly. When Qingdao is under the control of the subtropical high, the sea breeze is usually weaker, less than 2.5 m s^-1 throughout the day, and begins later, between 1300 and 1500 LST. In this case, the direction of the sea breeze is variable from easterly to southeasterly. Most sea breezes in Qingdao are very shallow, up to 300 meters deep. Strong sea breezes can reach 1.5 km in depth and can push as far as 100 km inland. If the Huanghai sea breeze moves inland and meets the sea breeze of the Jiaozhou Bay in the western part of Qingdao, the sea breeze will strengthen and form three boundaries due to the interaction of the two sea breezes.

Study on Possible Mechanism of Terrain Influence on Cold-flow Snowstorm

[Objective] The research aimed to study the possible mechanism of terrain effect on cold-flow snowstorm.[Method] By using the meso-scale numerical model(WRF),a cold-flow snowstorm weather process in Shandong Peninsula was carried out numerical simulation and terrain sensitivity contrast test.The possible reason of terrain effect on falling zone and strength of snowstorm was deeply analyzed from water vapor,thermodynamic field and so on.[Result] The mountain terrain in Shandong Peninsula had great influences on falling zone and strength of cold-flow snowstorm.The strength of snowstorm obviously increased,and the snowfall center obviously moved northward.The main reason was that terrain caused the low-level wind field convergence and vertical movement in the troposphere strengthened.Then,the spatial distribution of water vapor and snow water content in the cold-flow snowstorm process obviously changed.So,the whole snowstorm process was affected.[Conclusion] The mountain terrain in Shandong Peninsula was the important element which needed to be focused on considering in the forecast analysis of cold-flow snowstorm weather process.

A Homogeneous Linear Estimation Method for System Error in Data Assimilation

In this paper, a new bias estimation method is proposed and applied in a regional ensemble Kalman filter （EnKF） based on the Weather Research and Forecasting （WRF） Model. The method is based on a homogeneous linear bias model, and the model bias is estimated using statistics at each assimilation cycle, which is different from the state augmentation methods proposed in pre- vious literatures. The new method provides a good estimation for the model bias of some specific variables, such as sea level pres- sure （SLP）. A series of numerical experiments with EnKF are performed to examine the new method under a severe weather condi- tion. Results show the positive effect of the method on the forecasting of circulation pattern and meso-scale systems, and the reduc- tion of analysis errors. The background error covarianee structures of surface variables and the effects of model system bias on EnKF are also studied under the error covariance structures and a new concept ＇correlation scale＇ is introduced. However, the new method needs further evaluation with more cases of assimilation.

Analysis of Formation Mechanism of Two Successive Heavy Rainfall Processes on the Edge of the Subtropical High

Based on sounding and ground observation data,GPS/MET and FY-2 E satellite data,NCEP/NCAR reanalysis data（ 1°× 1°）,the formation mechanisms of two successive heavy rainfall processes on the edge of the subtropical high were analyzed. The results showed that the two heavy rainfall processes were caused by weak westerly troughs on the edge of the subtropical high at 500 h Pa,and there was strong southwest jet stream at 850-700 h Pa. As the low-level southwest jet stream intensified and moved northwards,heavy rainfall began. When the jet stream weakened,heavy rainfall ended. The heavy rainfall areas had good consistency with the high-value areas of CAPE,the high-value tongue of low-level water vapor flux,water vapor convergence center and warm advection center. Water vapor monitoring by GPS/MET had certain denotative meaning to the short-term prediction of heavy rainfall. The minimum TBB of convective cloud clusters was between-62 and-78 ℃,and the corresponding hourly maximum precipitation was 40-90 mm. In the heavy rainfall process,mesoscale vortexes occurred at 850 h Pa and below,but the scale was small,with weak low pressure but significant cyclonic circulation. The most intense rainfall was generated at the center of warm advection in the southeast of the vortex center at 925 h Pa. In the first heavy rainfall process,the mesoscale vortexes moved less,while strong rainfall was induced by strong upward movement in the southeast of the vortexes. In the second heavy rainfall process,low-level cold air invaded from the northwest into the vortexes to form cyclones and moved northeastwards. Heavy rainfall happened in the warm zone in front of cold front,and convective instability energy was high. Rainfall intensity was high,and rainfall range was large.

Mesocyclone Evolution and Differences between Isolated and Embedded Supercells

A total of 61 supercells with mesocyclones lasting for at least 6 volume scans were investigated. These storm parameters and mesocyclone parameters were counted and compared to determine the salient differences between isolated supercells and embedded supercells in different regions. The results showed that the mesocyclone parameters had different evolution characteristics in three stages of mesocyclone. The storm parameters, mesocyclone parameters and severe weather phenomenon had significantly differences between isolated supercells and embedded supercells. The mesocyclone parameter differences determined the differences in the reflectivity structure and weather phenomenon. The higher base and top of mesocyclone for isolated supercells indicated that the isolated supercells had higher maximum reflectivity, maximum reflectivity height, cell-based vertically integrated liquid and top of storm cell, and significantly higher probability of hail or large hail than the embedded supercells. The descending lower base of mesocyclone at its mature stage in the region of Jianghuai Plain indicated that the supercells in this region had a higher probability of mesocyclone-induced tornado.

STUDY ON MECHANISM OF EL NINO EVENT OCCURRENCE

A possible mechanism is put forward in this paper for El Nino events from the viewpoint of plate tec- tonics and oceanic geology.A number of the data are cited to illustrate the views that sea-bottom volcanic ac- tivities and hot springs may cause El Nino events.

Comparative Experiments on the Effect of Radar Data Assimilation and Increasing Horizontal Resolution on Short-term Numerical Weather Prediction

To examine the effect of radar data assimilation and increasing horizontal resolution on the short-term numerical weather prediction, comparative numerical experiments are conducted for a Huabei （North China） torrential rainfall event by using the Advanced Regional Prediction System （ARPS） and ARPS Data Anal- ysis System （ADAS）. The experiments use five different horizontal grid spacings, i.e., 18, 15, 9, 6, and 3 km,respectively, under the two different types of analyses： one with radar data, the other without. Results show that, when radar data are not used in the analysis （i.e., only using the conventional observation data）, increasing horizontal resolution can improve the short-term prediction of 6 h with better representation of the frontal structure and higher scores of the rainfall prediction, particularly for heavy rain situations. When radar data are assimilated, it significantly improves the rainfall prediction for the first 6 h, especially the locality and intensity of precipitation. Moreover, using radar data in the analysis is more effective in improving the short-term prediction than increasing horizontal resolution of the model alone, which is demonstrated by the fact that by using radar data in the analysis and a coarser resolution of the 18-km grid spacing, the predicted results are as good as that by using a higher resolution of the 3-km grid spacing without radar data. Further study of the results under the radar data assimilation with grid spacing of 18-3 km reveals that the rainfall prediction is more sensitive to the grid spacing in heavy rain situations （more than 40 mm） than in ordinary rain situations （less than 40 mm）. When the horizontal grid spacing reduces from 6 to 3 km, there is no obvious improvement to the prediction results. This suggests that there is a limit to how far increasing horizontal resolution can do for the improvement of the prediction. Therefore, an effective approach to improve the short-term numerical prediction is to combine the radar data assimilation with an optimal horizontal resolution.