Abstract:The authors used soil heat flux data observed at 17 stations of the Chinese Ecosystem Research Network (CERN) from 2004 to 2007 to analyze the seasonal and spatial variation of the soil surface heat flux. The soil heat flux changed from negative to positive at the beginning of February and became negative again around September. It remained positive from March to August then became negative from December to January. The soil heat flux showed seasonal variation over the northeast and northwest regions of China while it had little seasonal variation over the Yangtze River basin. Over the plateau region, the heat flux was relatively small and varied only slightly throughout the year. The general spatial distribution pattern of the soil heat flux over China was larger in northern China in spring and summer and in southern China during fall and winter. The annual mean soil heat flux was higher over the black land areas of northeast China, the northwest desert region, the north Loess Plateau, and the Sichuan Basin regions, but had negative values over the lower reaches of the Yangtze River and the alluvial regions of the lower reaches of the Yellow River. This study provides good references for further studies of soil climate formation.

Abstract:The atmospheric boundary layer over the Lanzhou suburb in the Yuzhong area was analyzed at the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL). Micro Pulse Lidar (MPL-4B) data was retrieved by the wavelet transform method and a simulation was performed using the Weather Research Forecast (WRF) model with its two boundary layer parameterizations schemes: YSU and MYJ. The results showed that the Lidar retrieval data and the simulated boundary layer height were in agreement. The WRF with YSU scheme reflected the convection boundary layer well; the WRF with MYJ scheme showed good results in simulating the dynamic boundary layer. The boundary layer over SACOL started to develop around 0800 LST and reached its maximum height at 1700 LST. The analysis showed that the thermic convection boundary layer can reach an altitude of more than 2 km, and the dynamic boundary layer can reach 1.5 km. The thermic convection boundary layer decreases faster than the dynamic boundary layer.

Abstract:The circulation conditions and characteristics of ground- and high-level meteorological elements of continuous radiation and rain types of fog in southwestern Hubei are analyzed using boundary detection and automatic ground observatory data. The following results are reported: 1) The inverse overlay of a blocking high-pressure ridge and southern trough benefited the occurrence of rain fog in southwestern Hubei. 2) The ground-level visibility and relative humidity exhibited a significant inverse relationship. Rain fog maintenance was nearly synchronous with the precipitation. 3) Ground-level visibility and cloud droplet concentration were more significant than the rain fog inverse relationship with the occurrence of radiation fog. Visibility and rain fog content also exhibited a significant inverse relationship with the occurrence of radiation fog; however, such a relationship did not exist between visibility and rain fog. Low ground-wind speed or calm wind commonly co-existed with radiation and rain types of fog. 4) The upper inversion layer was stronger, the lower inversion layer was weaker, and multi-inversion layers occurred with radiation fog. The bottom inversion layer of the rain fog was higher than that of radiation fog, although the inversion layer was not always present. However, two­-three inversion layers occurred with rain fog. 5) Low boundary-layer wind speed and weak convective activity benefited both fog types occurring in mountainous regions. 6) The saturated air layer height of radiation fog was lower than that of mist.

Abstract:With binomial coefficient smoothing and Morlet wavelet analysis, the anomaly time characteristics, inter-annual climate, and the spatio-temporal-varying characteristics of the temperature anomalies were analyzed using air temperature observations from stations in South Xinjiang from 1951 to 2007. The results show a pronounced difference in air temperature between winter and summer, mainly negative anomalies before the 1980s and a change to positive temperature anomalies after the 1980s; after 2000 a cooling trend appeared. The temperature deviation in summer was less than that in winter; this deviation appears in two waves during the 57-year period. Abnormally warm periods occurred in the late 1950s, the late 1970s, and at the beginning of this century, showing a 20-25-year oscillation. The frequency of abnormal temperature was 30% in winter and 26% in summer. There were more cold winters than warm winters, and more hot summers than cooler summers. More cold years appeared in the 57-year period than warmer ones and the extent of lower air temperature was greater than that of higher air temperature. The winter temperature in South Xinjiang showed two significant oscillations: a 6-10-year inter-annual cycle and an 18-20-year inter-decadal cycle. The summer temperature showed one significant oscillation: a 20-year inter-decadal cycle. The distribution of temperature and abnormal temperature varied with different decades and seasons. However, according to the long-term trend of air temperature, the region north of South Xinjiang (southern Tianshan Mountain) became hotter, while the Tarim basin and the region south of South Xinjiang became cooler. The temperature-ascending extent in winter was greater than that in summer in the calefactive area while the temperature-descending extent in summer was greater than that in winter in the descensional area.

Abstract:Based on 6-hour reanalysis data with 1°×1° resolution from NCEP and station observed data, a cold surge during 28-31 Dec 2004 was analyzed, showing the following results: (1) During this period, the cold surge moved southward, crossed the equator and influenced the weather of the southern hemisphere. The background circulation was favorable for the breakout of the cold surge: A combination of two troughs in the westerly at 200 hPa and a transversal trough that transformed to a normal one at 500 hPa, which categorized this cold surge as a “transversal trough” type. The Mongolia high remained quasi-stationary, and the strong north wind to the east of it was favorable for the cold surge breakout. (2) The kinetic budget shows that the barotropic kinetic genesis (BTG) and baroclinic kinetic genesis (BCG) are the most important terms of the kinetic budget equation. Initially, the BTG term was dominant; later, the influence of the BCG term increased to equal that of the BTG. After 31 Dec, the kinetic genesis and strong wind zone both decreased obviously. (3) The available potential energy (APE) budget indicates a good correlation between the release of APE and the wind at 850 hPa. The release of APE was favorable for the wind increase at low tropospheric levels and influenced mostly the high levels while having only a slight influence on the middle levels of the troposphere.

Abstract:Using observed daily 2-m air temperature data during 1990-2007 and hourly measurements during 2004-2007 recorded at 14 meteorological stations in Beijing, we investigated the annual, seasonal, and diurnal variations of the surface air temperature among four different areas of Beijing: The urban area (UA), suburban area (SA), north mountainous area (NMA), and south mountainous area (SMA). Distinct features were observed in the four areas. For all time scales, due to the urban heat island effect, the maximum surface air temperature was observed in UA, followed by SA, SMA, while the minimum was in NMA. During 1990-2007, surface air temperatures in all the four areas showed a significant warming trend, with the largest warming rate being in UA. The difference in surface air temperature between UA and the other areas was season-dependent. The difference in surface air temperatures between UA and SA and between UA and NMA were largest in winter and smallest in summer, while the largest difference in air temperatures between UA and SMA occurred in the summer, and the smallest was in spring. The minimum daily range of the surface air temperature was observed in UA in each season while the maximum was in SMA. Comparing the surface air temperature of Beijing Observatory with the four areas, the best fit was with UA while significant differences were observed with the other areas at all time scales.

Abstract:The simultaneous equation from the Lorenz model and its error equation without linear approximation were obtained in this study. Theoretical analysis revealed that the simultaneous equation can be transformed to a special operator equation with a property such that all the orbits obtained from the equation will converge to a finite volume. In addition, the equation demonstrates that the divergence of the flow has a negative value, which implies that the volume of the orbit in phase space approaches zero; therefore, all points will be attracted to a low-level dimensional curve surface. These two properties of the simultaneous equation make the evolution of error for the Lorenz system approach to an attractor. The mean absolute error is constant due to the certainty of probability density distribution of the error attractor; this property can be used to understand the phenomena of a small error in the Lorenz system saturating after a lengthy integration. The location and the number of attractor’s centers are obtained from the stability analysis method, and the results are validated by numerical experiments. The figure of error attractor shows that it differs from the solution’s attractor in location, number, and structure. Moreover, the authors demonstrated a method of extending this error analysis for the Lorenz equation to general ordinary differential equations (ODEs). The property of error equations for ODEs has been obtained, and the relationships between the locations of stable points and stability properties for error systems and ordinary systems are reported.

Abstract:Two Canadian Warmings (CWs) in December 1965 and November 1968 were chosen to investigate the circulation characteristics of CWs. Weak warming was observed at the middle and lower levels of the stratosphere in the two CW cases. Accompanying the weak warming, the westerly in the stratosphere changed to an easterly one, but lasted only a short while. The circulation anomaly in both CW cases was weaker compared to that in the stratospheric sudden warming (SSW). The “pre-conditioned” process that was observed in the SSW case was not observed in the two CW cases. As the main factor of the stratospheric disturbance, the upward planetary wave was enhanced prior to and after day 0 of the two CW cases, unlike in the SSW case. Arctic Oscillation (AO) evolution was employed to show the downward stratospheric vortex circulation anomaly. Although the two CWs caused an AO anomaly in the high stratosphere, the AO anomaly barely reached the lower troposphere.

Abstract:Using observational data from 97 meteorological ground stations in Hunan Province, the temporal and spatial characteristics and the variation trend of the glaze of Hunan Province were analyzed by EOF (Empirical Orthogonal Function), REOF (Rotated Empirical Orthogonal Function), linear regression, Mann-Kendall mutation, and wavelet analysis and the variation trend was compared with the mountain station data. The results indicate that the glaze occurred mostly between November and March of the following year; the spatial distribution of glaze days showed a higher incidence in the South and East and to windward, and a lower incidence in the North and West and to leeward. There were two high value centers and three low value centers distributed among the high and low value regions. The spatial distribution of the number of glaze days showed characteristics of regional consistency and a discrepancy in the reverse variation between the south and north, which can be classified into three anomaly areas: South and North Hunan, Central and Northwest Hunan, and Northeast Hunan. The yearly glaze days in both Hunan and Nanyue station present the same periodic change of 2, 4, 9, and 24 years. The glaze days converse more or less frequently between period of 2 and 4 years. There is a clear oscillation pattern of 9-year glaze day before the late 1970s. The 24-year glaze day exists during the four transition years in the early 1960s, mid-1970s, early 1990, and mid-2000. There is a significant decreasing trend in the number of glaze days in Hunan over the past 60 years, while the variation tendency in Nanyue station is not obvious although significant inter-annual and inter-decadal variations exist in Nanyue station.

Abstract:With conventional rain gauge data, radio-soundings, and NCEP 1°×1° reanalysis data, 12 rainstorm events along the east slope of the western Sichuan Plateau during 2004-2010 were analyzed. The weather patterns and environmental parameters during the formation and development of the convective rainstorms were investigated and the role of the western Sichuan Plateau in the formation of the convective rainstorms was evaluated. A set of idealized numerical simulations of the area’s topography were carried out to verify the results based on observations and the WRF mesoscale numerical model and the mean vertical profile calculated from plateau-upstream radio-soundings of the 12 convective rainstorms. The results are as follows: The plateau low pressure system moving into the Sichuan Basin is the main weather occurrence affecting the topographically convective rainstorm formation and development. With a low system moving into the Sichuan Basin, the southwest (south) flow in the lower troposphere evolves into a southeast (east) flow, the occurrence of which is the main cause of the topographically convective rainstorm formation. The air column contains sufficient moisture and convective available potential energy (CAPE) for the formation and development of the topographically convective rainstorm. The CAPE shows a clear diurnal variation with a peak phase during 1400LST to 2000LST, which is beneficial to the convective rainstorm formation and development. Due to the topographic Fr of the lower southeast (east) flow being slightly less than 1, the forced ascent and blocking of the around-flow may coexist when the air flows up the plateau. The air flow climbing in the topographical buffer zone and the cyclonic shear induced from the around-flow are both favorable for the initiation and development of the convective rainstorms. Lastly, a physical concept model is developed for the convective rainstorm formation in the buffer zone of the western Sichuan Plateau.

Abstract:Many vertical sections of Mesoscale Convective System (MCS) detected by CloudSat satellite in regions of high humidity have a structural trait whereby the equivalent potential temperature is close to uniform in the vertical. This is called the moist neutral stratification, commonly found in East Asia in low or medium-high latitudes, over land or sea. Further information regarding the centroid distribution of MCSs was obtained from geostationary satellite cloud infrared image, and the NCEP reanalysis data was used to diagnose some profiles of atmospheric parameters over the centroid of the MCSs. The statistical results show that a moist neutral stratification structure was common in the MCSs. The role that moist neutral stratification plays in the initiation and development of a MCS is discussed from a kinetic and thermodynamic point of view.

Abstract:Soil samples at 7 cm and 15 cm depths under a Korean pine and broadleaf mixed forest at Changbai Moun- tain, Northeast China, were collected with PVC tubes with resin cores at bases to study seasonal and annual changes in soil net N ammonification, net N nitrification, and net N mineralization after the addition of N sources such as (NH₄)₂SO₄, NH₄Cl, and KNO₃. In the non-fertilized plots, net N ammonification of the soils at both depths accounted for 53%-72% of soil net N mineralization, whereas the ratio of soil net N ammonification to net N mineralization was re- duced by 37%-66% in the KNO₃ added soils at a high dose, and the ratio was increased by 86%-92% in the NH₄⁺-N treated soils. The addition of N sources, particularly NH₄⁺-N, appeared to increase soil net N mineralization, and the stimulating effect reduced with time of fertilization. Both net N ammonification and net N mineralization rates of the soils at the 7 cm depth were greater than those of the soils at the 15 cm depth, particularly after the addition of NH₄Cl. In combination with results of previous studies, stepwise regression analysis showed that 38% of the variability in annual net N mineralization of forest soils at various global sites could be attributed to the annual wet atmospheric N deposition. In addition, 50% of the variability in annual soil net N mineralization could be attributed to the annual wet atmospheric N deposition, the pH value of forest organic horizon, and the ratio of total C to total N. The results are beneficial for pre- dicting soil net N mineralization at regional forest stands and its responses to environmental changes.

Abstract:Bromide was considered to improve the box-model of lower stratospheric ozone heterogeneous photochemical reactions established by Wang and Yang (2007). To obtain further understand of the relationship of stratospheric ozone levels and human activities, the authors investigate the nonlinear response of the lower stratospheric ozone toward the changes in emission intensity of sulfuric acid aerosol, chloride, oxynitride, and bromide. On the basis of the analysis, the authors conclude that when the chloride emission intensity deviates from standard levels, the mutual interaction between aerosol and chloride, oxynitride, and bromide can affect the photochemical system nonlinear response and change the topological structure of parameter space.

Abstract:Wind speed prediction is a key factor for wind farm planning and the operational planning of power grids; accurate forecasting of wind speed can minimize the scheduling errors and in turn increase the reliability of the electric power grid and reduce the power market ancillary service costs. Based on the mesoscale model WRF(Weather Research and Forcasting) for wind speed forecasting, combined with model prediction and statistical analysis using an intelligent optimization algorithm we have greatly improved the forecasting precision of wind speed, employing a new method to correct the model errors. In view of the climatic feature of Chinese wind farms, the wind speed prediction program in China has been enhanced.