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Detection of nighttime sea fog/stratus over the Huang-hai Sea using MTSAT-1R IR data

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Acta Oceanologica Sinica 2009年第2期28卷 23-35页

作者： GAO Shanhong WU Wei ZHU Leilei FU Gang HUANG Bin Physical Oceanography Laboratory Ocean University of China Qingdao 266003 China Shandong Provincial meteorological Institute Jinan 250031 China national meteorological center China Meteorological Administration Beijing 100081 China

A dual channel difference （DCD） method is applied to detect nighttime sea fog/stratus over the Huanghai Sea using the infrared （IR） data of shortwave （3.5-4.0 μm） and longwave （10.3-11.3 μm） channels from the Multi-functional Transport Satellite （MTSAT）-IR, i.e., shortwave minus longwave brightness temperature difference （SLTD）. Twenty-four sea fog events over the Huanghai Sea during March to July of 2006 and 2007 are chosen to determine a suitable value of SLTD for nighttime sea fog/stratus detection, and it is found that the value of-5.5-2.5℃ can be taken as a criterion. Two case examples of sea fog events are especially demonstrated in detail utilizing the criterion, and the results show that the derived sea fog/stratus coverage is quite reasonable. This coverage information is very helpful to analyze the formation and evolution of sea fog/stratus during night and can provide sea fog researchers with observational evidences for model results verification. However, more efforts are needed to further obtain vertical extent information of sea fog/stratus and attempt to discriminate between sea fog and stratus.

关键词： Huanghai Sea nighttime sea fog MTSAT-1R dual channel difference method

An improvement on summer regional climate simulation over East china: Importance of data assimilation of soil moisture

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Chinese Science Bulletin 2010年第9期55卷 867-873页

作者： HU YaMin1,2,3, DING YiHui4 & LIAO Fei2 1 Institute of Tropical and Marine Meteorology, china meteorological administration, Guangzhou 510080, china 2 Guangdong Climate center, Guangzhou 510080, china 3 Chinese Academy of meteorological Sciences, beijing 100081, china 4 national Climate center, china meteorological administration, beijing 100081, china

The Newtonian relaxation is used to assimilate data from the Second Global Soil Wetness Project (GSWP2) into the initial field for soil moisture in a regional climate model (i.e., BCC_RegCM 1.0, hereinafter called RegCM). The results show that different nudging parameters can improve the simulation of the air temperature and the precipitation to some extent in summertime season over East china. When the nudging intensity is 0.5 and nudging duration is 5 days, the result is desirable. Introducing the data assimilation of soil moisture into RegCM, the amelioration is not only in the spatial distribution pattern but also in the magnitude of the temperature and the precipitation. More specifically, the assimilation experiments have corrected the systematical cold bias of the air temperature and the precipitation on the low side, which is much closer to the observation compared with the control experiment. On the whole, the assimilation experiments shed light on the fact that the simulated bias in the original RegCM may be affected by the description of soil moisture in the land surface process. Therefore, the effect of soil moisture in RegCM should be paid more attention in the future.

关键词： soil moisture Newtonian relaxation data assimilation regional climate simulation

Numerical simulation of topography effects on the “00.7” severe rainfall in beijing

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Progress in Natural Science:Materials International 2005年第9期15卷 818-826页

作者： ZHANG Chaolin1**, JI Chongping1, KUO Yinghwa2, FAN Shuiyong1, XUAN Chunyi3 and CHEN Min1(1. Institute of Urban Meteorology, china meteorological administration, beijing 100089, china 2. Mesoscale and Microscale Meteorology Division, national center for Atmospheric Research, Boulder, CO 80307-3000, USA 3. beijing meteorological Bureau, beijing 100089, china) Institute of Urban Meteorology China Meteorological Administration Beijing 100089 China. Mesoscale and Microscale Meteorology Division National Center for Atmospheric Research Boulder CO 80307-3000 USA. beijing meteorological Bureau Beijing 100089 China

In an effort to study the severe rainfall event of 4—5th July 2000 in beijing (with 24h accumulated precipitation of 240 mm), we perform numerical simulations to investigate this event using the MM5v3.6 model. The model is initialized with the MM5/WRF 3DVAR analysis, which incorporates the ground-based GPS precipitable water vapor, automatic and conventional meteorological observations in its assimilation step. For 24 h accumulated precipitation forecast, the threat scores are 0.72, 0.76, 0.67 and 0.63, for thresholds of 1, 5, 10, and 20 mm, respectively. Holding other factors unchanged, sensitivity experiments were conducted with different topographic resolutions of 110, 50 and 3.7 km to investigate the topographic effects on precipitation over the beijing area. In these sensitivity experiments, we attempt to preserve the realistic orographic distribution in the model topography under the condition of keeping the dynamic-thermodynamic consistency of the initial model atmosphere to the extent possible. Results indicate that the unique topographic distribution and variations in the beijing area play an important role in determining the location, distribution and intensity of heavy precipitation.

关键词： topography heavy rainfall 3DVAR ground-based GPS numerical simulation.

Research on the dry intrusion accompanying the low vortex precipitation

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Science china Earth Sciences 2007年第9期50卷 1396-1408页

作者： YAO XiuPing1,2,3, WU GuoXiong1, ZHAO BingKe4, YU YuBin3 & YANG GuiMing2,5 1 LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, beijing 100029, china 2 Institute of Heavy Rain, china meteorological administration, Wuhan 430074, china 3 china meteorological administration Training center, beijing 100081, china 4 Shanghai Typhoon Institute of china meteorological administration, Shanghai 200030, china 5 national meteorological center of the china meteorological administration, beijing 100081, china 1. LASG Institute of Atmospheric Physics Chinese Academy of Sciences Beijing 100029 China 2. Institute of Heavy Rain China Meteorological Administration Wuhan 430074 China 3. china meteorological administration Training center Beijing 10081 China 4. Shanghai Typhoon Institute of china meteorological administration Shanghai 200030 China 5. national meteorological center of the china meteorological administration Beijing 100081 China

By employing the 6.7μm satellite vapor cloud images and NCEP/NCAR 1°×1° reanalysis datasets, the characteristics and mechanism of the dry intrusion, as well as its impacts on the low vortex precipita- tion at the Meiyu front are explored in this paper. It is found that the formation,development and main- tenance of the low vortex precipitation at the Meiyu front are closely related to the evolution of the dry intrusion. The dry intrusion is characterized by high potential vorticity (PV), low humidity and cold air. The dry intrusion exhibits as an obvious dark zone on vapor cloud images, an area in which atmos- pheric relative humidity is lower than 60%. However, the features of the dry intrusion on the vapor im- ages are clearer than that of the humidity field, for the former is the digital vapor cloud images with high temporal and spatial resolution, and it can be used to explore the finer characteristics of the develop- ment, evolution and supplement of the intrusion during the development of the low vortex. The dry intrusion impacts accompanying the low vortex precipitation at the Meiyu front come from all levels of the troposphere, with the strongest intrusion located at the upper troposphere. The dry and cold air intrudes the vicinity of the low vortex from the upper isentropic surface to the lower one, slanting eastward from lower to higher level. The low vortex precipitation region is usually situated in front of the dry intrusion where the relative humidity gradient is higher. The research also reveals that the mechanism of the dry intrusion is that the high potential vorticity descends from the upper troposphere to the lower level, therefore, the dry intrusion can be used as an important index of the high PV forcing. To the west of the low vortex precipitation, the upper level northerlies descend across the isentropic surface, then the dry cold advection can trigger the instable development in the mid-low troposphere. The dry intrusion enhances the low vort

关键词： Meiyu front, low vortex precipitation, dry intrusion, mechanisim, vapor image, potential vorticity, relative humidity

An analysis of interplanetary sources of geomagnetic storm during November 7-8, 1998

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Chinese Science Bulletin 2010年第9期55卷 853-858页

作者： LE GuiMing1,2,3, TANG YuHua1, ZHENG Liang5 & LIU LianGuang4 1 Department of Astronomy, Nanjing University, Nanjing 210093, china 2 national center for space weather, china meteorological administration, beijing 100081, china 3 Key Laboratory of Radiometric Calibration and Validation for Environmental Satellites, china meteorological administration (LRCVES/CMA), beijing 100081, china 4 North china Electric Power University, beijing 102206, china 5 Graduate University of Chinese Academy of Sciences, beijing 100049, china

We analyzed the properties of the solar wind appeared during November 7–8, 1998. Results show that the spaceship ACE spotted a shock (hereinafter referred to as the first shock) at 07:33 UT, November 7. The sheath appeared from the first shock to 22:00 UT November 7. A magnetic cloud-like (MCL) was observed during the period from 22:00 UT November 7 to 11:50 UT, November 8. Another shock was observed at 04:19 UT, November 8 (the second shock). It is apparent that the second shock has entered the rear part of the MCL (MCL_2), though the former part of the MCL (MCL_1) was not affected by the second shock. The main phase of the geomagnetic storm is split into three steps for the convenience of SYM-H index analysis. Step 1 covers the period from the sudden storm commence (SSC) at 08:15 UT, November 7 to the moment of 22:44 UT, November 7. Step 2 starts from 22:44 UT, November 7 and ends at 04:51 UT, November 8. The last step runs from 04:51 UT, November 8 to 06:21 UT, November 8. Step 2 has played a key role in the main development phase of the geomagnetic storm. Analysis of the solar wind properties associated with the main phase shows that the three steps in the main phase have sheath, MCL_1, and MCL_2 as their respective interplanetary source. Specifically, the sheath is covered by the solar wind data from 07:33 UT to 22:00 UT, November 7, MCL1 by the solar wind data from 22:00 UT, November 7 to 04:19 UT November 8, and MCL_2 by the solar wind data from 04:19 UT to 05:57 UT, November 8. MCL_1 had a strong and long lasting so UTh directed magnetic field, allowing it to play a key role in the development of the main phase. MCL_2 made a much smaller contribution to the main development phase, compared with MCL_1.

关键词： geomagnetic storm magnetic cloud interplanetary shock sheath south component of interplanetary magnetic field

Forecasting the summer rainfall in North china using the year-to-year increment approach

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Science china Earth Sciences 2009年第4期52卷 532-539页

作者： FAN Ke1, LIN MeiJing1,2 & GAO YuZhong3 1 Nansen-Zhu International Research center, Institute of Atmospheric Physics, Chinese Academy of Sciences, beijing 100029, china 2 Graduate University of the Chinese Academy of Sciences, beijing 100049, china 3 Heilongjiang meteorological administration, Harbin 150030, china Nansen-Zhu International Research center Institute of Atmospheric Physics Chinese Academy of Sciences Beijing 100029 China Graduate University of the Chinese Academy of Sciences Beijing 100049 China Heilongjiang meteorological Administ

A new approach to forecasting the year-to-year increment of rainfall in North china in July-August (JA) is proposed. DY is defined as the difference of a variable between the current year and the preceding year (year-to-year increment). NR denotes the seasonal mean precipitation rate over North china in JA. After analyzing the atmospheric circulation anomalies associated with the DY of NR, five key predictors for the DY of NR have been identified. The prediction model for the DY of NR is established by using multi-linear regression method and the NR is obtained (the current forecasted DY of NR added to the preceding observed NR). The prediction model shows a high correlation coefficient (0.8) between the simulated and the observed DY of NR throughout period 1965-1999, with an average relative root mean square error of 19% for the percentage of precipitation rate anomaly over North china. The prediction model makes a hindcast for 2000-2007, with an average relative root mean square error of 21% for the percentage of precipitation rate anomaly over North china. The model reproduces the downward trend of the percentage of precipitation rate anomaly over North china during 1965-2006. Because the current operational prediction models of the summer precipitation have average forecast scores of 60%-70%, it has been more difficult to forecast the summer rainfall over North china. Thus this new approach for predicting the year-to-year increment of the summer precipitation (and hence the summer precipitation itself) has the potential to significantly improve operational forecasting skill for summer precipitation.

关键词： annual increment North china precipitation prediction prediction skill

Numerical simulations of the bi-level and branched structure of intracloud lightning flashes

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Science china Earth Sciences 2006年第6期49卷 661-672页

作者： TAN Yongbo1, TAO Shanchang1, ZHU Baoyou1, MA Ming2 & LU Weitao2 1. School of Earth and space Sciences, University of Science and Technology of china, Hefei 230026, china 2. Chinese Academy of meteorological Sciences, beijing 100081, china 1. School of Earth and space Sciences University of Science and Technology of China Hefei 230026 China 2. Chinese Academy of meteorological Sciences Beijing 100081 China

Intracloud (IC) lightning flashes have been simulated in fine resolution (12.5 m) by using a bidirectional stochastic lightning parameterization scheme within 2-dimensional domain. The simu-lated results show that the IC flashes have a bilevel channel structure and the altitudes of the hori-zontal channels are at the same heights of potential wells, which are supported by the previous VHF source observations and balloon soundings of electric field profile in the thundercloud. Further con-clusions are: (1) After an IC flash is initiated near the boundary between positve and nagetive charge zone, the negative (or positive) leader tends to propagate into the positive (or negative) charge zone. Both types of positive and negative IC flashes have been reproduced and their polarity depends on the up and down disposition of the positive and negative charge regions. (2) The extension range of leaders is correlative with the cloud charge distribution. The leader is possible to extend through the inverted charge region all over where it is extending, but keeps away from the isolated charge area of the same polarity. (3) The channel structures also depend on the electric potential distributions in the thundercloud. Before propagating into the central area of potential wells, the leader tends to extend along the direction with the maximum of potential gradient. Once extending away from the center of potential wells, the leader tends to extend along the direction with the slowest potential change. (4) The IC flash channels have the fractal feature with fractal dimension 1.45 before leaders pass through the central area of charge regions. The exponent decreases rapidly once leaders extend into the low-density charge regions. (5) The induced charges of opposite polarity are deposited in the leader channels within preexisting positive and negative charge regions during IC flash discharges. This causes a new and complicated charge distribution in the thundercloud, and the potential

关键词： IC, lightning parameterization, branched bilevel structure, fractal feature, propagation tendency.

A New Approach to the On-Orbit Evaluation of Point Spread Function of Thermal Infrared Images With Applications to FY-2 Satellite Products

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A New Approach to the On-Orbit Evaluation of Point Spread Fu...

Approximate Solution of the Nonlinear Parallel Diffusion Theory of Charged Particles

作者： Qiang Guo,Changjun Yang,and Caiying Wei the national Satellite meteorological center,china meteorological administration,beijing 100081,china,the Key Laboratory of Radiometric Calibration and Validation for Environmental Satellite,china meteorological administration,beijing 100081,china

Spatial characteristics of thermal infrared(TIR) images are generally described by image-derived point spread function(IDPSF) for sampled imaging *** investigators working on IDPSF on-orbit evaluation focus on visible and near-infrared images and pay little attention on TIR ones,the reason of which lies on the fact that the assumption of an observed target with an ideal step profile is not suitable for TIR band. A new approach for TIR images is proposed here based on a more common slope-profile model,where the transition features, i.e.,the sample number(N) and the beginning position of slope interval,are extracted from the observed *** results show that the estimation performance will be increased, with lower noise level as well as higher system modulation transfer function value at half of normalized spatial frequency(MTF) or smaller *** a good performance system with noise squared-root variance(SRV) no more than 1.0 count and MTF between 0.3 and 0.4,the relative error between simulated and estimated MTF\s is less than 20%.The IDPSF of FY-2C satellite TIR band is estimated,and the derived MTF0.5 is properly close to on-ground testing *** image quality of FY-2C TIR band has been improved by using Wiener filtering and the estimated IDPSF,which eventually benefits the cloud detection product with more detectable low fractus and increased detection accuracy by about 1%in *** a step-profile target as a special case of this model,the proposed approach is also suitable for visible and near-infrared images.

关键词： Index Terms—Infrared imaging optical image processing optical transfer functions.

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Approximate Solution of the Nonlinear Parallel Diffusion The...