Abstract:To discuss the possibility of applying a numerical Weather Research and Forecasting (WRF) model to wind power forecasting, the summer and winter hourly wind speed forecasting performance of the WRF model used in Rudong, Jiangsu Province, is analyzed in this paper. It is determined that the WRF model can forecast winter wind speed in Rudong 24 h in advance very well with a correlation coefficient as high as 0.61 compared to observations and is statistically significant at the 0.01 level. Similarly, the forecasts with leading times of 48 h and 72 h are also sufficiently accurate, according to the correlation coefficients. In summer, however, forecasting is less accurate, although the correlation coefficient of the 24 h leading forecast is 0.59, which is still statistically significant at the 0.01 level. The forecasting of wind speed in Nantong was also examined with observed data and was determined to be more accurate than that in Rudong in both winter and in summer. For a larger domain, the performance of wind forecasting is also analyzed. Results show that the performance of the WRF model is better for ocean than for land and is better in winter than in summer. In general, the forecasted wind speed is greater than the actual wind speed and the performance of the WRF model foresting differs significantly according to location and season. Essentially, short-term wind forecasting is valuable and is worthy of further investigation.

Abstract:Moderate-resolution Imaging Spectroradiometer (MODIS)-Enhanced Vegetation Index (EVI) data reported during 2000-2009 have been analyzed to study recent trends in vegetation greenness over the northern part of China at the beginning of the 21st century. The results showed that the afforestation area was larger than the degraded area in the northern part of China during the last 10 years, and the regional total mean annual EVI increased by 5.97%. Seasonal EVI increased significantly, and trends in summer and winter were larger than those in spring and autumn. The sparsely vegetated area declined, unit area EVI increased, and vegetation activity rose during the study period. In addition, EVI changes in the northern part of China exhibited relatively large spatial heterogeneity. The Northeast China Plain, North China Plain, Loess Plateau, and Xinjiang agriculture regions experienced marked increases, and part of Northeast China and West China experienced declining trends. Such patterns are attributed primarily to regional climate changes and human activities such as ecological construction and urbanization.

Abstract:The authors report on the first-time use of 1961-2006 hourly visibility data from 15 airports to investigate the interdecadal variation of dust-haze episodes in the North China Plain. The preliminary results show that (1) the evolution of the frequency of dust-haze weather showed interdecadal change characteristics from the 1990s until recent years, with dust-haze episodes evolving from local to regional scale. (2) Between the 1970s and 1990s the frequency of dust-haze episodes increased in the megacities (e.g. Beijing, Shijiazhuang), while decreasing in mid-size and small cities; this has important implication for dust-haze control strategies. (3) Before the 1970s the frequency of dust-haze episodes in the Beijing area (about 100 days per year) was almost the same as in the Shijiazhuang area; however, after 1975 the dust-haze episode frequency in the Shijiazhuang area increased rapidly and recent figures show that it is more than 100 d-higher than in the Beijing area. Considering the impact of urbanization on dust-haze conditions and the fact that the extent of urbanization in the Beijing area is much larger than that in the Shijiazhuang area, this interesting initial find deserves further investigation.

Abstract:The K-means clustering method was used to determine quality-controlled hourly surface air temperature data of 123 automatic weather stations in the Beijing area. The sites of these stations were classified into the following four zones, that is urban stations, suburban stations, west and north mountainous area stations, and southwest and northeast mountainous area stations. Monthly and diurnal temperature variations and diurnal temperature range (DTR) of the four zones were analyzed and hourly and monthly urban heat islands were investigated. K-means clustering proved advantageous in classifying temperature zones, which were correlated with the terrain and underlying surfaces of the stations. The DTR of the urban zone was revealed to be smaller than that in suburban and mountainous areas. The west and north mountainous areas exhibited the highest DTR values. All zones exhibited high DTR values in February, May, and October. The urban heat island effect in the Beijing area was stronger in winter and at night. In the daytime, the urban heat island effect appeared to be stronger in summer than that in other seasons. From March to August, the urban heat island effect was the weakest.

Abstract:Datasets of daily precipitation, wind speed, and weather phenomena of 71 stations during 1960-2009 and experimental observations of precipitation from three stations are used to estimate wind-induced errors in winter snowfall records over northeastern China, and to analyze the effects of wind-induced under-catch on long-term winter snowfall trends. The results show that winter snowfall is generally undervalued. Although the region’s average annual snowfall was measured at 15.1 mm, the corrected snowfall was 22.5 mm, which indicates an average error of 7.5 mm, or relative error of approximately 34.1%. In recent years, the gauge catch rate has increased due to the weakening of surface wind speed resulting from urbanization and micro-environmental change surrounding the stations, which have led to an overestimate of winter snowfall trends in the study region. This analysis shows a 50-year linear trend of winter snowfall of 0.4 mm/10 a when original precipitation data are included and a long-term trend of winter snowfall at 0.1 mm/10 a when adjusted data are used. The effect of wind-induced error on the estimates of winter snowfall trends is particularly significant in the southern part of the study region, with an overestimate for long-term trends reaching ?1 mm/10 a, or approximately 64.3% in terms of relative bias.

Abstract:Simulation and forecasting of wind fields in the urban canopy layer (UCL) is important for developing and implementing measures for atmospheric emergency response. To reflect the impact of the UCL on wind fields and to fulfill rapid emergency response requirements, an urban canopy wind profile parameterization method (UCPM) proposed by MacDonald (2000) is coupled with the mesoscale model MM5. The performance of the UCPM is tested with observations from a 325-m meteorological tower in Beijing from 18 Jul to 6 Aug 2010. The results demonstrate that the UCPM accurately reproduces wind profiles in the UCL under neutral, stable, and unstable conditions with normalized mean bias of 78%, 12%, and 4%, respectively, and normalized mean error of 78%, 52%, and 21%, respectively. The UCPM shows excellent performances at heights of 8, 15, 32, and 47 m within the UCL with normalized mean bias of 2%, -26%, 25%, and 60%, respectively, and normalized mean error of 54%, 46%, 52%, and 73%, respectively. Comparison with the Monin-Obukhov similarity parameterization (MO) reveals that the UCPM significantly improves simulations of wind speeds in the UCL. Under neutral, stable, and unstable conditions, the normalized mean error of MO is 420%, 176%, and 184%, respectively, and UCPM is reduced to 78%, 52%, and 21%, respectively; at heights of 8, 15, 32, and 47 m within the UCL, the normalized mean error of MO is 283%, 184%, 227%, and 167%, respectively, and UCPM is reduced to 54%, 46%, 52%, and 73%, respectively.

Abstract:A comparison of data detected by wind profiler and balloon-mounted radars revealed no significant differences between the two types under conditions of weak wind power. The variation rules of space and time were studied by using the data of wind profiler radar at the seaside of Huilai. The results show that the wind profiler radar has stronger detecting capability on the vertical structure of three-dimensional winds and can detect sea-land breeze vertical shear in real time. Such data could be used to analyze the rules of pollutant diffusion and migration in coastal areas. In addition, data obtained by the wind profiler radar was studied to determine the rule of periphery wind shear of Typhoon Chanthu. The results show that the wind profiler radar also has stronger detecting capability on the typhoon peripheral sinking airflow area of high-altitude wind in a three-dimensional wind vertical structure. Moreover, this type of radar can detect the rules of typhoon space shear in real time to improve the efficiency of the typhoon prevention in coastal areas.

Abstract:The sunshine duration daily data for 1956-2005, which was made available by the National Meteorological Information Center, is used to calculate sunshine duration trends, abrupt changes, temporal and spatial distribution, and seasonal variation through empirical orthogonal function (EOF) and Mann-Kendall analyses. The results show that: (1) Significant decreases in sunshine duration occurred over much of China during the latter half of the 20th century. The decreasing trend halted until the 1990s, after which time it was maintained at a low state. (2) Most of the meteorological stations happened abrupt climate change in 1980. (3) This change was significant, particularly in the eastern half of the country. (4) The change in summer sunshine duration is a major contributor to this decrease.

Abstract:In this paper, the empirical orthogonal function (EOF) method is used to analyze the upper sea temperature anomalies in the North Pacific during winter with higher resolution Simple Ocean Data Assimilation (SODA) data. The spatial pattern of the second EOF mode is similar to the classical North Pacific Gyre Oscillation (NPGO) mode, as is the time series. Therefore, the second EOF mode is hereafter referred to as the NPGO mode. Results indicate that the NPGO exists not only at the sea surface, but also at the entire upper ocean. The spatial structure of the NPGO mode is characterized by a dipole-like structure in the meridional direction with maximum anomalous centers located near 170°W above a depth of 100 m. The anomalously warm band between 25°N and 30°N extends from 120°E to the Mideast Pacific, while the northern area is anomalously cool. In addition, obvious temperature anomalies exist from the sea surface to the upper sea level at the eastern area of Honshu Island. The formation of this spatial feature has a close relationship with the North Pacific Oscillation (NPO) mode and the wind stress anomalies in the mid-latitude westerly zone, which is the direct reason for the NPGO modes. The time series of the NPGO mode shows obvious decadal variation of approximately 13 years. The five-year moving average of the time series shows that its amplitude has become larger since the middle 1970s, and the climate transition of 1976/1977 and 1988/1989 show peak values of this series. Finally, the NPGO index of the sea temperature anomalies in the upper North Pacific during winter is defined, which can reflect the decadal variation of NPGO mode more accurately.

Abstract:The atmospheric circulation anomalies in winter and spring associated with the year-to-year increments of summer extreme precipitation event frequency over the Huaihe River valley (HRF) were analyzed during 1962-2005 to identify five key HRF predictors by using a year-to-year incremental approach. These indicators include the North Pacific Oscillation (NPO) in winter, the Antarctic Oscillation (AAO) in December, sea level pressure over the region of the south Indian Ocean and Bering Sea in March and April (MA), and the meridional wind shear between 850 hPa and 200 hPa over the Indo-Australian plate region in MA. A prediction model for year-to-year increments of HRF is established by using the multi-linear regression method. The predicted value of each year’s increment of HRF is added to the observed value within a particular year to yield the HRF forecast. Cross-validation testing shows that the prediction model has a high skill for HRF with a correlation coefficient of 0.67 during 1962-2005. Thus, this prediction model has a high potential for accurate HRF forecasting.

Abstract:Through data analyses and sensitive experiments with the general circulation model (GCM), the relationship and influence of the sea surface temperature anomalies (SSTA) in the North Pacific on the meridional dipole mode of sea level pressure (SLP) in the Asia-Pacific region are studied in this paper. The data analyses show two critical regions of SSTA in the northwestern Pacific corresponding to the anomalous meridional dipole mode of the SLP in winter in the Asia-Pacific region. In particular, the SSTA in the (40°N-55°N, 150°E-160°W) region shows a positive correlation and that in the (20°N-35°N, 125°E-170°W) region shows a negative correlation to index I_ME of the meridional dipole mode of the SLP. The data analyses also show that the impact of SSTA in those two critical regions on the meridional dipole mode of the SLP in the Asia-Pacific region is mainly passed through the effect of heat flux anomalies. The results of sensitive experiments with the GCM show that the SSTA in two critical regions of the Northwestern Pacific play a specific role in exciting the meridional dipole mode of the SLP in winter in the Asia-Pacific region. In region I (42°N-62°N, 145°E-165°E), the negative SSTA is more effective than the positive SSTA in exciting the negative phase of the meridional dipole mode of the SLP; the positive SSTA in region II [(22°N-42°N, 135°E-175°E) and (26°N-42°N, 175°E-170°W)] is more effective than the negative SSTA in region I in exciting the negative phase of the meridional dipole mode of the SLP. However, the position of the excited negative meridional dipole mode of the SLP deviates a certain distance when there is negative SSTA in region I alone or positive SSTA in region II alone. Because the negative SSTA in region I coordinates with the positive SSTA in region II, the excited negative meridional dipole mode of the SLP is remarkable.

Abstract:Previous analyses have focused on the relationship between sea surface temperatures (SSTs) over tropical oceans and summer typhoons over the western North Pacific (WNPTYF); however, few studies have been conducted on other oceans. To determine the relationship between the WNPTYF and SSTs over the middle-high latitude Indian Ocean (MHIO), their independence, significance, and hysteretic characteristics are examined in this study. The results show that SSTs over MHIO can influence WNPTYF independently when the effect of El Ni?o-Southern Oscillation (ENSO) is not considered. The annual change in SST over MHIO can indicate WNPTYF’s yearly change, in addition to that over the tropical East Pacific, with greater accuracy. Synthesis of the SST anomalies over the two areas is useful when the WNPTYF forecast is abnormal. Results also show that SSTs over MHIO influence WNPTYF in hysteresis, with significant correlation in the previous stage, from January to April, and week correlation at the same time, from June to September. The lagged influence of SSTs over MHIO to WNPTYF indicates that the former affects the latter through continuity of the abnormal atmospheric action over the Southern Hemisphere rather than by SST steadiness. However, for better understanding of this mechanism, further research is required.

Abstract:By analyzing surface meteorological observations and air quality monitoring data (O₃, NO_x, and PM10) at two stations from 2 April to 7 April 2008, in Nanjing, eastern China, the inverse correlation between O₃ and particulate matter is determined. A photochemical box model is employed to interpret the possible mechanism. The simulation shows that elevated concentration of particulate matter can increase the aerosol optical depth by 20%-40% and reduce averaged photolysis rates of NO₂ and O₃ and concentration of OH and HO₂ by 20%-30% and 20%-50%, respectively, which leads to a 30%-40% decrease in the net photochemical production rate of O₃. The results indicate that the effects of atmospheric particles on photochemistry and the oxidation ability of the atmosphere are responsible for the reduction of the observed surface O₃ concentration.

Abstract:The process and the methods in the study of synoptic cyclone was reviewed. The contents included Bjerknes’ synoptic cyclone mode in the early period, the life cycle of Bjerknes’s and Solberg’s synoptic cyclones, and the temperature structures of the cyclone described by Petterssen. Meanwhile, the impacts of latent heating and topography on the cyclone development were briefly introduced. Besides, the authors recounted the Petterssen cyclone development theory, slantwise vorticity development theory, the cyclone-genesis theory based on the quasi-geostrophic (QG) -w equation and the isentropic potential vorticity (IPV) thinking, and the academic view of the cyclone development induced by ultra-long wave development and upper level jet-stream acceleration. All these provided the historic background, the ideas and the methods in the cyclone studies.