Vol.27, NO.3, 2016

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An Analysis System Using Rapid-updating 4-D Variational Radar Data Assimilation Based on VDRAS
Chen Mingxuan, Gao Feng, Sun Juanzhen, Xiao Xian, Liu Lian, Wang Yingchun
2016, 27(3): 257-272. DOI: 10.11898/1001-7313.20160301
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Abstract:
On the basis of further improvement and development of Variational Doppler Radar Analysis System (VDRAS), a rapid-updating 4-D variational analysis system focusing on convective-scale numerical simulation and aiming at nowcasting convective storm has been preliminarily set up and tuned. The system is based on rapid-updating 4-D variational assimilation (RR4DVar) techniques of multi-Doppler-radar observations, a 3-D cloud-scale numerical model with simplified microphysics scheme which includes rainwater evaporation cooling and precipitation sedimentation processes, and an adjoint model. The system can rapidly get low-level 3-D analysis fields including convective-scale dynamical, thermo-dynamical and microphysical structures with 12-18-min updating cycles by assimilating both reflectivity and radial velocity observations from 6 CINRAD Doppler radars in Beijing-Tianjin-Hebei region using the RR4DVar scheme. It also integrates 5-min observations from regional auto weather stations (AWS) and forecast results from a meso-scale numerical model. Allowing for a strong convective storm case occurred in the region on 22 July 2009, simulated results from a series of sensitivity experiments including control, full-troposphere and full-microphysics, meso-scale background, and radar data assimilation are analyzed. These results are also compared and evaluated using intensive local observations from four wind profiler radars, two microwave radiometers, and two boundary layer towers. Some key factors for the system to produce appropriate analysis fields are illuminated. The system using low-level settings with the simplified microphysics scheme has comparable skill with full-troposphere settings and full-microphysics scheme. In the system, most significant RR4DVar assimilation of radar observations can be obtained using two or three scanning volumes from each radar within an assimilation window. As an effective supplement to radar observations on the ground, the AWS data is also very important on the RR4DVar assimilation of radar observations and simulations of dynamical and thermo-dynamical structures at several lower model levels. The meso-scale background and dynamical constraint for the RR4DVar assimilation of radar observations are sensitive to convective-scale simulation in both cold and warm start updating cycles. Results also indicate the system can produce robust pre-storm environment features including low-level inflows, vertical wind shear, low-level small-scale convergence, updraft and warm tongues. On the other hand, storm-associated convective-scale structures including cold pools and outflows can also be reasonably analyzed by the system.
Extended Range Forecast Experiment for Rainfall Based on the Real-time Intraseasonal Oscillation
Chen Guanjun, Wei Fengying, Yao Wenqing, Zhou Xuan
2016, 27(3): 273-284. DOI: 10.11898/1001-7313.20160302
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Abstract:
1 State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing 1000812 Beijing Meteorological Observatory, Beijing 100089Intraseasonal oscillation (ISO) in South China Sea summer monsoon (SCSSM) plays a key role in controlling the intraseasonal variations of rainfalls over southern China, and it can be described with the leading pair of empirical orthogonal functions (EOFs) for the 110°-120°E averaged 850 hPa zonal wind (U850). An index for monitoring the SCSSM ISO is built on a pair of principal component (PC) time series of EOFs mentioned above, and then the NCEP Climate Forecast System Version 2 (NCEP/CFSv2) hindcasts and stepwise regression statistical method are employed, to explore extended range forecast (ERF) of rainfall intraseasonal variations.First, southern China is divided into three regions using rotated empirical orthogonal functions (REOFs), where the incidence rate of regionally persistent heavy rainfall (RPHR) is closely linked to the intraseasonal variation in rainfall. Based on the spatial structure of the first three REOFs, three intraseasonal rainfall indices are constructed by averaging the 30-60-day filtered precipitation over the typical regions and taken as predictands. Second, EOF1 of the 850 hPa zonal wind over the SCS and southern China mainly represent the ISO mode controlling the intraseasonal rainfall south of the Yangtze River, while EOF2 leads to the intraseasonal out-of-phase rainfall over South China and the Yangtze-Huai River Basins. Projection of the daily data onto the leading pair EOFs of 850 hPa zonal wind yields PC time series that serves as an effective filter for ISO without the need for bandpass filtering and making the PC time series two effective indices for real-time use. The pair of PC time series that form indices are called real-time indices for SCSSM ISO. Finally, 28 years of NCEP/CFSv2 reforecasts are used which include wind at 850 hPa and grid values of rainfall extending up to 30-day lead time. Characteristics of SCSSM ISO are also found similar to observations in the NCEP/CFSv2 reforecasts. Forecast models are built on the historical reforecast values of indices (predictors) and rainfall time series (predictands), and use forecast values of indices to predict the future values of rainfall time series varying mostly on the intraseasonal time scale. This method can significantly improve the ERF results (10-30 days) of intraseasonal variations of rainfalls in southern China, reduce system errors, avoid losses of forecasting data and correct negative correlations between forecasts and observations caused by bandpass filtering.
Empirical Orthogonal Function-analogue Correction of Extra-seasonal Dynamical Prediction of East-Asian Summer Monsoon
Cheng Yabei, Ren Hongli, Tan Guirong
2016, 27(3): 285-292. DOI: 10.11898/1001-7313.20160303
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Abstract:
In terms of the dataset of the second generation climate prediction model of Beijing Climate Center, BCC_CSM1.1(m) hindcasts in February from 1991 to 2010, the model is assessed on its performances in predicting five monsoon indices including the East Asian summer monsoon index (EASMI), the western North Pacific summer monsoon index (WNPSMI), the East Asian monsoon index (EAMI), the Indian summer monsoon index (ISMI) and the East Asian summer monsoon intensity index (EASMII). A correction method based on the empirical orthogonal function (EOF) analysis and the analogue analysis, called the empirical orthogonal function-analogue correction of errors (EOF-ACE) is used to correct the modes which are poorly predicted by the model.Through EOF analysis, the coordinated variation of the five monsoon indices can be reflect by the obtained modes. In addition, according to the principle of ensemble forecast, three similarity indices are used to select the similarity years. The correction process is divided into two parts, which are linear component correction and non-linear component correction.Assessments indicate that the EASMI and the WNPSMI are predicted well by BCC_CSM1.1(m). However, the prediction result of EAMI, ISMI and EASMII is poor. Through EOF-ACE correction, the model prediction skill of the monsoon indices originally unreasonable are improved, but it's unsatisfactory for the rest indices. The linear component correction mostly shows higher skill than non-linear component correction in cross-validation. However, for independent validation, the effect of non-linear component correction is mostly better than linear component correction, which displays application prospects.However, the EOF-ACE has barely effects on indices whose deviations are originally small, and correlation coefficients of some summer monsoon indices between observations and predictions are still not significant through correction. It is necessary to make further analysis on the inter-annual variation of those indices, and look for the relevant external force factors.
Impact of 10-30-day Oscillation Intensity over the Tropical Northwest Pacific Ocean on the South China Sea Summer Monsoon
Li Chunhui, Liu Yan, Li Xia, Pan Weijuan
2016, 27(3): 293-302. DOI: 10.11898/1001-7313.20160304
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Abstract:
Based on the NCEP reanalysis data and ERSST sea surface temperature (SST) data, using statistical methods, 10-30-day significant sub-seasonal variability periods are extracted from the summer (Jun-Aug) convective in the tropical western Pacific, and these oscillations have different effects on the South China Sea summer monsoon intensity at different scales. At inter-annual time scale, a positive significant correlation is found between the intensity variation of 10-30-day oscillation over the tropical northwest Pacific Ocean regions (TWPI), and the correlation coefficient is 0.635. Influences of TWPI on the South China Sea summer monsoon intensity are mainly regulated by ENSO. Because of the asymmetric response of the lower troposphere Northwest Pacific atmospheric circulation to ENSO, TWPI is much more significant in El Niño developing years than in La Niña years. During strong TWPI years, the SST anomalies are El Niño pattern, which induces anomalously enhanced westerly in the South China Sea, the Philippines and the tropical northwest Pacific Ocean. The westerly anomalies generate strong positive vorticity shear, resulting in abnormal cyclonic circulation, and enhance TWPI and summer monsoon intensity through the wind-evaporation feedback mechanism. On the contrary, in La Niña years, the anticyclonic anomaly circulation result in TWPI weakening and the monsoon strength weakening. Under different inter-decadal backgrounds, TWPI does not show a significant change in the decadal trend, mainly slightly weaker (1958-1976), slightly stronger (1977-1993) and slightly weaker (1994-2011) change. The trend of the summer monsoon intensity inter-decadal changes are more obvious, namely, much stronger, slightly weaker and much weaker. The overall change of vertical shear and water vapor-convection are consistent with TWPI, but are not consistent with the summer monsoon. Vertical shear of wind field and water vapor-convection play important roles on the inter-decadal variation of TWPI, but not for the summer monsoon. The thermal contrast between sea and land is the key factor that leads to the inter-decadal change in the South China Sea summer monsoon.
Characteristics of NO2 Tropospheric Column Density over a Rural Area in the North China Plain
Jin Junli, Ma Jianzhong, Lin Weili, Zhao Huarong
2016, 27(3): 303-311. DOI: 10.11898/1001-7313.20160305
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Abstract:
NO2 tropospheric vertical column densities (VCD) at Gucheng Eco-meteorological Observation Experiment Station (GCH) in Hebei Province from September 2008 to September 2010 are retrieved from the scattered sunlight spectra, measured by a multi-axis differential optical absorption spectroscopy (MAX-DOAS), and its characteristics are analyzed then.It shows that the mean seasonal NO2 tropospheric VCDs are high in winter (5.14×1016 cm-2) and low in summer (1.28×1016 cm-2). The mean value in winter is a little lower than that in urban Beijing and much lower than that in spring and summer. Averaged diurnal variations are always low at noon and high towards evening for the whole year. The varying amplitude in winter is the biggest among all seasons and the concentration shows a rising up trend in the late afternoon. Less variation can be seen during the day in spring and autumn, and they decrease slowly in summer, reaching a minimum value after noon. The phenomena can be explained by seasonal differences of sources and sinks of tropospheric NO2.The tropospheric NO2 over GCH site is mainly affected by the transport from sectors of SW, SSW, NE and ENE, where the major NO2 emission sources in North China are located. It's interesting to note that the NO2 tropospheric VCDs over GCH site is higher than that over Xianghe site (another rural site in North China) in winter. Backward trajectories analyses show that in winter two sites have a distinct difference of pollutant sources, which are causes of their discrepancy.Patterns of seasonal variations are quite the same for NO2 tropospheric VCDs retrieved from MAX-DOAS and satellite observation product OMNO2d, as well as the mixing ratios of in situ NO2 measurements. Compared with results from MAX-DOAS, a systematic underestimation of OMI satellite observation for NO2 is found in the rural North China area, as those found in urban Beijing and Shanghai megacities. The individual NO2 VCDs retrieved from MAX-DOAS and the surface NO2 mixing ratios are highly correlated, with an apparently higher correlation coefficient (R=0.738) than that between OMNO2d and surface mixing ratios (R=0.639).It's evident that column density levels of tropospheric NO2 can be much better captured by MAX-DOAS observations than other measurements. As a result, much more emphasis should be given on the development of MAX-DOAS observation network. Furthermore, the application of MAX-DOAS measurements on validation and correction of satellite data should be strengthened.
Bright Band Analysis in Yangtze-Huaihe Region of Anhui Using Data Detection from C-FMCW Radar
Jin Long, Ruan Zheng, Ge Runsheng, Wu Linlin, Dai Xiuyong
2016, 27(3): 312-322. DOI: 10.11898/1001-7313.20160306
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Abstract:
Being different from the scanning radar, the vertical detection radar is used to analyze the micro-physics process in the precipitation cloud and the fusion layer from the vertical structural feature and the evolution process of the precipitation cloud. The C-FMCW vertical pointing radar adopts the solid-state system, bistatic antenna technology, and the demodulated signal processing adopts two-dimensional FFT signal processing technology to extract the distance information and the spectrum distribution information in the range bin. The vertical resolution of data is from 15 m to 30 m and the time resolution is from 1 s to 3 s, and the minimum reflectivity at 15 km height is-20 dBZ. Compared with the neighboring CINRAD/SA radars at Bengbu and Hefei, the reflectivity calibration difference is less than 1 dB, and root mean square error is less than 2.02 dB. Using C-FMCW radar detective data from June to August in 2013 at Dingyuan of Anhui, the bright band of the precipitation cloud detection data in 46 h are identified. The cumulative rainfall reaches 340.3 mm, during which 55620 precipitation cloud vertical profiles are obtained. 39.1% of precipitation clouds show clear bright band structural feature and during the occurrence of the bright band the precipitation makes up 15% of the total amount. During the Yangtze-Huaihe rainy season, the bright bands appear in stratiform cloud, convective cloud and the mixed precipitation system. In the stratiform cloud, the bright band is most stable and maintains longer. The bright band appears in the decay stage of the convective precipitation and the melting increase is obviously slower. The aggregation increase is of the strongest in the mixed precipitation system, after which the continuous bight band structure is broken by the strengthened convection distribution. The micro-physics process in the fusion layer is complicated. Excluding effects of phase changes and particle number concentration changes, the vapor change in the melting process is given. The maximum reflectivity in the melting process is used to analyze the layering process. It shows the melting process in the upper layer is mainly absorption growth, while in the lower layer is breakup process.
The Application to Temperature Advection Retrieval Based on Wind Profile Radar Data
Shan Nan, He Ping, Wu Lei
2016, 27(3): 323-333. DOI: 10.11898/1001-7313.20160307
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Temperature advection is a basic physical variable in the weather prediction. It directly leads to the change of atmospheric thermal structure and further brings about the alteration of atmospheric physics field, and can reflect the development of weather systems better. In recent years, the technology of wind profile radar (WPR) improves greatly, and WPR data has both high precision and high spatial-temporal resolution and could continuously provide the distribution of horizontal winds over time. Based on the concept of temperature advection and the principle of thermal wind, retrieving the temperature advection with high precision and spatial-temporal resolution is feasible by algorithms established.The temperature advection information is retrieved from WPR data at Yanqing Station of Beijing, whose results are compared to temperature advection prediction products of Global Medium Range Forecast System of T639L60 (hereinafter, T639L60 model). A cold air invasion process on 15 Nov 2014 in the night is analyzed in detail and 6 more samples occurring from Sep to Nov in 2015 are statistically analyzed for evaluation too. Results show that the horizontal wind of the WPR is highly consistent with the wind prediction data of T639L60 model within a certain amount of prediction time (about 6 to 12 h). The order of magnitude is consistent and the value is close between the retrieval of temperature advection by the WPR data and the initial data of T639L60 model. The quality of retrieving temperature advection depends on the quality of horizontal wind profile data. Temperature advection prediction products of T639L60 model and the real-time retrieval products are accordant within a period of 6-12 h depending on the temporal scale of different weather system. The derivation gradually increases as the prediction time lengthens, sometimes even reverse prediction advection attribute may appear. Temperature advection with real-time, continuous attribute and high precision can be provided through WPR observations whose time and vertical resolution is 6 min and 120 m, respectively. And some prediction results can be calculated using the measured results by linear extrapolation in a short period. Thus, the precision of numerical forecast can be improved with WPR data assimilated in the future. Preliminary results show that the real-time 3D products and forecast products of temperature advection with high precision, spatial and temporal resolution could be generated through high quality WPR network data assimilated.
A Tornado in South China in May 2015
Chen Yuanzhao, Yu Xiaoding, Chen Xunlai, Wang Shuxin, Luo Ming
2016, 27(3): 334-341. DOI: 10.11898/1001-7313.20160308
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A severe tornado event near Baoan International Airport of Shenzhen, Guangdong Province on 11 May 2015 is investigated. Based on the routine upper-air, surface automatic weather station (AWS), Doppler radar, wind profile data and NCEP 6-hour analysis data (1°×1°), the environmental condition, structure and evolution are analyzed. The intensity of this tornado belongs to the F1 tornado intensity category. The tornado event occurs in front of 500 hPa trough, warm and moist area ahead of 850 hPa shear lines and the warm section before surface cold front. It is significant that the atmospheric convective instability is strengthened by the low temperature and humidity increasing, and the dry cold air behind 500 hPa trough moving eastward. The calculation of atmospheric convective parameters shows that there is powerful convective available potential energy (CAPE), strong low-level vertical wind shear and abundant water vapor in atmospheric environment before the tornado occurs. The analysis of Doppler radar products also indicates that the storm has a life span lasting about 1 hour, during which its echo top extends the height of nearly 5 km. The tornado initially comes from a quasi-linear convective system along the surface convergence line. The quasi-linear convective system moves slowly down and becomes a massive comma echo, finally develops into hooked echo, and the tornado is detected near the weak echo area. The echo of the strongest center value reaches 62 dBZ. The tornado locates at the edge of the strongest echo gradient region near the weak echo region, which indicates that the strong updraft contributes most to the tornado. The mesocyclone first appears in the middle cell of the storm, beginning at 3 km height and then developing upward and downward. The height of the strong core (no less than 50 dBZ) is below 5 km in the tornado event, making it a low centroid convective system. The mesocyclone always shows cyclonic rotation characteristics from originated to maturity in the radial velocity chart. When the rotational speed increases, the radius of the mesocyclone decreases and the largest vertical vorticity associate with the mesocyclone is 1.2×10-2 s-1. The distance separating the strongest inbound and outbound radial velocities (called velocity couplet) is reduced from 8 km to 6 km. The mesocyclone deepens gradually downwards, producing the tornado. When the tornado is underway, strong divergence occurs at the storm top above the tornado. Therefore, in operational work more attention should be paid to the sudden change of echo shape and rapidly developing cyclone vortex.
Radar Echo Characteristics of Thunderstorm Gales and Forecast Key Points in Hebei Province
Wang Fuxia, Yu Xiaoding, Pei Yujie, Yang Xiaoliang, Meng Kai, He Lihua
2016, 27(3): 342-351. DOI: 10.11898/1001-7313.20160309
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Using Xinle CINRAD-SA radar data at Shijiazhuang about 262 cases of thunderstorm from 2006 to 2008, radar echo characteristics of thunderstorm gales in Hebei Province are analyzed. It is found that the main characteristics can be divided into three categories, including the bow echo, band echo and bulk echo. The band echo accounts for 66.8%, the bow echo is 19.8%, and the isolated bulk cell echo is 13.4%. So the band echo is the main echo of thunderstorm gale. The main radar echo characteristics of thunderstorm gale are bow echo, gust front and radial velocity large value area, and all of them are thunderstorm gale warning indicators. Based on the above radar echo features, 66% thunderstorm gales can be forecasted. All bow echo thunderstorm gales can be forecasted, but they only account for 19.8%. Gust fronts can be observed only 16.8% of cases, and thunderstorm gales high speed value area can be observed 65.3% of cases. Therefore, the high speed value area is the most important characteristics of radar echoes. The formation rate of high speed value area is generally earlier than bow echo and gust front, so the thunderstorm gale can be forecasted earlier by using this characteristic.There are some limitations in the thunderstorm gale warning based on radar echoes. Sometimes the gust front echo will cause velocity less than 17 m/s, when the early warning may be false alarm. The gust front echo mainly concentrates in the boundary layer, and cannot be detected if it's far away from the radar. But when it's close to the radar, the gust front echo are difficult to identify solely due to clutter noise. Therefore, thunderstorms warning based on the gust front echo only will lead to missing alarms. For small scale isolated bulk echo, there are no significant differences between the reflectivity characteristic of gale, precipitation and thunderstorm. If the gamma scale convergence appears on the radial velocity, it's not the unique features to the thunderstorms gale. Therefore, the isolated blocky echoes cause thunderstorms more difficult to make the gale warning.At present, the radial velocity of the large value area is a warning indicator of the thunderstorm gale. Whether there is an exceptional case needs to be verified in the future.
Risk Assessment of Maize Chilling Injury in Northeast China
Tang Yuxue, Guo Jianping
2016, 27(3): 352-360. DOI: 10.11898/1001-7313.20160310
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The northeast region is an important maize production area in China. Chilling injury is a main meteorological disaster for maize, and yields of maize decrease over 15% in several serious chilling injury years. A new index of maize chilling injury is established, and the risk of the chilling injury is assessed. Based on previous research, the damage inflicted temperatures in each growing period of maize (including seedling stage, jointing stage, flowering stage and filling stage) are determined. A new chilling injury index of cold accumulated temperature (TCA for short) is defined, which can quantitatively describe strength of chilling injury, and its value is the difference between damage inflicted temperature and environment temperature. Calculation formulas of daily TCA, periodical TCA and annual TCA are given.According to decadal mean TCA, four regions of maize chilling injury in Northeast China are divided. Based on the analysis of relationship between annual TCA anomaly and annual yield reduction rates of the above regions, index of annual TCA anomaly in Northeast China is classified into 3 types: Chilling injury year but no damage, common damage year and serious damage year. Risks of chilling injury are calculated and regression equations are built. Finally, a model of space grid annual average TCA is constructed by geographical factors, including the latitude, longitude and altitude, and the probabilities of chilling injury are calculated by application of GIS. The risk index of maize chilling injury is a multiplication of disaster probability, vulnerability and exposure. Therefore, risks of maize chilling injury in Northeast China are assessed. The assessment shows that risks are low in the northern and the southern parts, while high in the western, middle and eastern areas. High risk regions include the northeast and northwest of Songnen Plain and the north center of Jilin Province, middle risk regions include the Sanjiang Plain, and risks are low in the north of Heilongjiang Province, the southeast of Jilin Province and the whole of Liaoning Province. These results may provide guidance for maize chilling injury prevention, loss reduction and planting structure adjustment in Northeast China.
Simulation of Various Connecting Patterns During the Lightning Connection Process Based on the Stochastic Lightning Leader Model
Liao Yihui, Lü Weitao, Qi Qi, Zhang Rong, Zhang Dongdong, Tan Yongbo, Zhang Yijun
2016, 27(3): 361-369. DOI: 10.11898/1001-7313.20160311
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Considering the observed fact that most upward connecting leaders (UCL) does not branch during downward negative cloud-to-ground (CG) strikes, the simulation scheme of upward positive leaders is modified based on the existing two-dimensional (2D) stochastic lightning model. In addition, two connecting patterns, i.e., the tip-to-tip connecting and the tip-to-lateral connecting (lateral strike) between the downward leader and the UCL are simulated during the process in which lightning strikes tall buildings. Sensitivity experiments are carried out on the connecting process between leaders during the process of lightning striking a tall building by altering the horizontal distance between the initiation point of the downward leader (at a height of 1000 m) and the tall building. Results indicate that when the value of d increases from 0 to 700 m, the probability of a lateral strike for the UCL generally exhibits a trend of first increasing and then decreasing. As the value of d increases, the length of the UCL exhibits an increasing trend, and the ratio of the part of the UCL above the connecting point accounting for the entire length of the UCL upon the lateral strike generally exhibits an increasing trend. The probability of each grounding position is under the influence of the horizontal distance. The UCL initiating from the top of tall structures is longer than that initiating from the ground or the side surface of tall structures. Furthermore, tall structures with different heights are also investigated.
Comparison and Analysis of Automatically-observed and Manually-observed Relative Humidity
Mao Jiajia, Mo Yueqin, Zhang Xuefen, Yang Yanhong, Guo Ran, Hu Shuzhen
2016, 27(3): 370-379. DOI: 10.11898/1001-7313.20160312
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In 2012, the artificial meteorological observation is replaced by auto weather station in China. More than 2300 surface weather stations begin to use automatic weather observation system, and only 8 national reference climatological stations retain long-term manual observation. Great changes have taken place in observational rules and methods of automatic weather stations comparing with manual observations. Inhomogeneity of data series may be caused by many causes and the change of observational instrument is an important one, and therefore comprehensive comparisons are demanded to gain understanding of their differences.In order to determine the comparability of automatically-observed and manually-observed relative humidity and find out differences between them, the integral point observations from 2007 to 2013 of 8 national reference climatological stations which retain long-term manual observation are analyzed. Analysis results show that the average relative humidity observed by automatic way is from-5.69% to-0.1% lower than that by manual way, and the standard deviation is 2.02%-4.71%. As the humidity rises, the system error of the two increases. Differences between automatically-observed and manually-observed relative humidity are most significant in summer, and related to the wind speed. The difference is obvious under low speed conditions and it decreases gradually as the wind speed increases. The observation of relative humidity is also influenced by the ambient temperature. There is no significant time difference between two types of the hourly observation. The daily variation of differences between automatically-observed and manually-observed relative humidity have a rising trend in the early morning when the relative humidity is higher, especially in the high humid area, and have a dropping trend in the afternoon when the relative humidity is low.The relative humidity data of 8 national reference climatological stations observed by inner screen psychrometer and the hair hygrometer which have some deviations between them, and there are some deficiencies in the measurement performance of humicap too. Besides, the background information of the instruments are not fully known. For all of these, the conclusion has some limitations, although some problems can be explained. It is recommended that the maintenance and calibration of humicap should be carried out regularly, and the performance of the humicap at low temperature should be further tested.
Effects of Cloud Parameter on Brightness Temperature Computation in Microwave Band
Gu Chengming, Wang Yunfeng, Zhang Xiaohui, Zhong Bo, Ma Xinyuan
2016, 27(3): 380-384. DOI: 10.11898/1001-7313.20160313
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The CRTM fast radiative transfer model is utilized to simulate channel brightness temperature of NOAA-K/AMSU-A. The research focuses on effects of cloud particles type, height and thickness on simulation of each channel brightness temperature. Results show that when there exists water cloud and rain cloud, the corresponding brightness temperature is larger; when there exists ice cloud, snow cloud, hail cloud or graupel cloud, the change of corresponding brightness temperature isn't very obvious. Effects of cloud on channel brightness temperature depend on the configuration of weighting function peaks and cloud top height. When cloud exists at multiple heights, if topmost cloud is thicker (2 km), brightness temperature value of corresponding channels depends on the highest cloud. When the cloud is relative thin, brightness temperature of channels lower or slightly higher than cloud top changes obviously. For those channels far higher than cloud top, their brightness temperatures are not sensitive to cloud thickness change.
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