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Relationships of along-the-track local variations of GPS RO impact parameter to strong local vertical gradient of wet refractivity in the tropics

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Science China Earth Sciences 2021年第11期64卷 2015-2026页

作者： Shengpeng YANG xiaolei zou Joint Center of Data Assimilation for Research and Application Nanjing University of Information Science&TechnologyNanjing 210044China

Atmospheric refractivity fields are more strongly affected by more water vapor in the tropical lower troposphere than elsewhere.In this study,based on model simulations,we first collocated the radio occultation(RO)data in 2009 from the Constellation Observing System for Meteorology,Ionosphere,and Climate(COSMIC)with CloudSat cloud profiling radar data.We then investigate where and why a RO ray path intersects with other simulated rays of impact heights above and/or below the impact height of the ray.Using the European Centre for Medium-Range Weather Forecasts ERA5 reanalysis as input to a raytracing observation operator,we show that the simulated impact parameters could vary along the ray in the tropical lower troposphere.For brevity,an intersection of a GPS RO ray path with rays above it or below it or both will be called an impact multipath.By overlapping simulated ray trajectories over the vertical and horizontal gradients of refractivity in 2D occultation planes,impact multipath occurrences are vividly illustrated.Statistical results show that the impact multipath is caused mostly by strong local vertical gradients of atmospheric wet refractivity mostly within 300 km horizontal distances from their perigee positions.The impact multipath occurs more frequently below 5-km impact height,with a maximum occurrence around the 3.4 km impact height(about 1.8 km geometric height).It is shown that both the simulated impact multipath phenomena and locally strong vertical gradients of wet refractivity are found in both cloudy and clear-sky conditions,and most frequently in presences of stratocumulus clouds.

关键词： GPS RO Multipath Troposphere

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Comparison of Advanced Technology Microwave Sounder Biases Estimated Using Radio Occultation and Hurricane Florence(2018) Captured by NOAA-20 and S-NPP

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Advances in Atmospheric Sciences 2020年第3期37卷 269-277页

作者： Xiaoxu TIAN xiaolei zou Earth Science System Interdisciplinary Center University of Maryland

The second Advanced Technology Microwave Sounder(ATMS)was onboard the National Oceanic and Atmospheric Administration(NOAA)-20 satellite when launched on 18 November 2017.Using nearly six months of the earliest NOAA-20 observations,the biases of the ATMS instrument were compared between NOAA-20 and the Suomi National Polar-Orbiting Partnership(S-NPP)satellite.The biases of ATMS channels 8 to 13 were estimated from the differences between antenna temperature observations and model simulations generated from Meteorological Operational(MetOp)-A and MetOp-B satellites’Global Positioning System(GPS)radio occultation(RO)temperature and water vapor profiles.It was found that the ATMS onboard the NOAA-20 satellite has generally larger cold biases in the brightness temperature measurements at channels 8 to 13 and small standard deviations.The observations from ATMS on both S-NPP and NOAA-20 are shown to demonstrate an ability to capture a less than 1-h temporal evolution of Hurricane Florence(2018)due to the fact that the S-NPP orbits closely follow those of NOAA-20.

关键词： ATMS NOAA-20 S-NPP biases calibration Hurricane Florence

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Quality control of AIRS total column ozone data within tropical cyclones

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Frontiers of Earth Science 2016年第2期10卷 222-235页

作者： Yin LIU xiaolei zou Center of Data Assimilation for Research and Application Nanjing University of Information Science & Technology Nanjing 210044 China Key Laboratory of Meteorological Disaster of Ministry of Education Nanjing University of Information Science & Technology Nanjing 210044 China Earth System Science Interdisciplinary Center University of Maryland College Park MD 20740-3823 USA

The Atmospheric Infrared Sounder （AIRS） provides infrared radiance observations twice daily, which can be used to retrieve total column ozone with high spatial resolution. However, it was found that almost all of the ozone data within typhoons and hurricanes were flagged to be of bad quality by the AIRS original quality control （QC） scheme. This determination was based on the ratio of total precipitable water （TPW） error divided by TPW value, where TPW was an AIRS retrieval product. It was found that the difficulty in finding total column ozone data that could pass AIRS QC was related to the low TPW employed in the AIRS QC algorithm. In this paper, a new two-step QC scheme for AIRS total column ozone is developed. A new ratio is defined which replaces the AIRS TPW with the zonal mean TPW retrieved from the Advanced Microwave Sounding Unit. outliers when the new The first QC step is to remove ratio exceeds 33%. Linear regression models between total column ozone and mean potential vorticity are subsequently developed with daily updates, which are required for future applications of the proposed total ozone QC algorithm to vortex initialization and assimilation of AIRS data. In the second QC step, observations that significantly deviate from the models are further removed using a biweighting algorithm. Numerical results for two typhoon cases and two hurricane cases show that a large amount of good quality AIRS total ozone data is kept within Tropical Cyclones after implementing the proposed QC algorithm.

关键词： AIRS total column ozone total precipitablewater mean potential vorticity quality control

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Bias characterization of ATMS low-level channels under clearsky and cloudy conditions

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Frontiers of Earth Science 2019年第2期13卷 277-289页

作者： Qi LI xiaolei zou Joint Center of Data Assimilation for Research and Application College of Atmospheric ScienceNanjing University of Information Science and Technology (NUIST)Nanjing 210044China Earth System Science Interdisciplinary Center (ESSIC) University of MarylandCollege ParkMD 20740-3823USA

The Advanced Technology Microwave Soun? der (ATMS) onboard the Suomi National Polar-Orbiting Partnership satellite is a cross-track scanning instrument containing 22 sounding channels in total.In this study,the bias characteristics of channels 1-6,which could have significant cloud contamination in heavy precipitation,are first analyzed based on the differences between ATMS observations (O) and model simulations (B) under clearsky conditions over oceans.Latitudinal dependencies of the biases of window channels 1-3 are greater than those of channels 4-6.Biases of all nadir-only observations examined in different latitudinal bands[μ1(φ)]are positive and no more than 7.0 K.Biases at higher latitudes are larger.Channels 1-5 have a generally symmetric scan bias pattern [μ2(α)].The global distributions of brightness temperature differences after subtracting the biases,i.e.,O-B-μ1(φ)-μ2(α),for channels 3-6 spatially match the liquid water path distributions.Excluding ice-affected observations,channel 3-6 O-B differences systematically increase as the liquid water path increases under cloudy conditions.Further investigation is needed to apply these findings for ATMS data assimilation under both clear-sky and cloudy conditions.

关键词： ATMS O-B clear-sky bias characteristics impact of clouds on biases

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Latitudinal and Scan-dependent Biases of Microwave Humidity Sounder Measurements and Their Dependences on Cloud Ice Water Path

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Advances in Atmospheric Sciences 2019年第5期36卷 557-569页

作者： Anqi CAI xiaolei zou Joint Center of Data Assimilation for Research and Applications Nanjing University of Information Science and Technology Earth System Science Interdisciplinary Center University of Maryland College Park

The relationship between differences in microwave humidity sounder(MHS)–channel biases which represent measured brightness temperatures and model-simulated brightness temperatures, and cloud ice water path(IWP) as well as the influence of the cloud liquid water path(LWP) on the relationship is examined. Seven years(2011–17) of NOAA-18 MHS-derived measured brightness temperatures and IWP/LWP data generated by the NOAA Comprehensive Large Array-data Stewardship System Microwave Surface and Precipitation Products System are used. The Community Radiative Transfer Model, version2.2.4, is used to simulate model-simulated brightness temperatures using European Center for Medium-Range Weather Forecasts reanalysis data as background fields. Scan-angle deviations of the MHS window channel biases range from-1.7 K to1.0 K. The relationships between channels 2, 4, and 5 biases and scan angle are symmetrical about the nadir. The latitudedependent deviations of MHS window channel biases are positive and range from 0–7 K. For MHS non-window channels,the latitudinal deviations between measured brightness temperatures and model-simulated brightness temperatures are larger when the detection height is higher. No systematic warm or cold deviations are found in the global spatial distribution of difference between measured brightness temperatures and model-simulated brightness temperatures over oceans after removing scan-angle and latitudinal deviations. The corrected biases of five different MHS channels decrease differently with respect to the increase in IWP. This decrease is stronger when LWP values are higher.

关键词： bias microwave humidity sounder ice water path Community Radiative Transfer Model

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Variations of sea ice in the Antarctic and Arctic from 1997-2006

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Frontiers of Earth Science 2014年第3期8卷 385-392页

作者： Huijie DONG xiaolei zou College of Atmospheric Science Nanjing University of Information Science & Technology Nanjing 210044 China Department of Earth Ocean & Atmospheric Science Florida State University Tallahassee 32304 USA

在极的区域的海冰是全球气候系统的重要部分。以便为南极和北极在海冰程度获得变化，这份报纸分析了特殊传感器微波 / 成像器(SSM/I ) 从 1997 年 3 月 1 日标明日期到 2006 年 12 月 31 日的海冰数据产品。在这个时期期间，海冰程度与... 详细信息

在极的区域的海冰是全球气候系统的重要部分。以便为南极和北极在海冰程度获得变化，这份报纸分析了特殊传感器微波 / 成像器(SSM/I ) 从 1997 年 3 月 1 日标明日期到 2006 年 12 月 31 日的海冰数据产品。在这个时期期间，海冰程度与趋势在南极增加了(0.5467

关键词：海冰面积南极北极全球气候系统组成部分数据产品威德尔海西太平洋

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Striping Noise Analysis and Mitigation for Microwave Temperature Sounder-2 Observations

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Advances in Atmospheric Sciences 2019年第7期36卷 711-720页

作者： xiaolei zou Xiaoxu TIAN Earth Science System Interdisciplinary Center University of Maryland College Park

The Microwave Temperature Sounder(MWTS)-2 has a total of 13 temperature-sounding channels with the capability of observing radiance emissions from near the surface to the stratosphere. Similar to the Advanced Technology Microwave Sounder(ATMS), striping pattern noise, primarily in the cross-track direction, exists in MWTS-2 radiance observations. In this study, an algorithm based on principal component analysis(PCA) combined with ensemble empirical mode decomposition(EEMD) is described and applied to MWTS-2 brightness temperature observations. It is arguably necessary to smooth the first three principal component(PC) coefficients by removing the first four intrinsic mode functions(IMFs) using the EEMD method(denoted as PC3/IMF4). After the PC3/IMF4 noise mitigation, the striping pattern noise is effectively removed from the brightness temperature observations. The noise level in MWTS-2 observations is significantly higher than that detected in ATMS observations. In May 2014, the scanning profile of MWTS-2 was adjusted from varying-speed scanning to constantspeed scanning. The impact on striping noise levels brought on by this scan profile change is also analyzed here. The striping noise in brightness temperature observations worsened after the profile change. Regardless of the scan profile change, the striping noise mitigation method reported in this study can more or less suppress the noise levels in MWTS-2 observations.

关键词： MWTS-2 striping noise temperature sounding microwave radiometry

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Impact of FY-3A MWTS radiances on prediction in GRAPES with comparison of two quality control schemes

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Frontiers of Earth Science 2014年第2期8卷 251-263页

作者： Juan LI xiaolei zou National Meteorological Center China Meteorological Administration Beijing 100081 China Department of Earth Ocean and Atmospheric Sciences Florida State University Tallahassee 32306 USA

The impact of Microwave Temperature Sounder （MWTS） radiances on the prediction of the Chinese Numerical Weather prediction （NWP） system-GRAPES （Global and Regional Assimilation and PrEdiction System） with comparison of two Quality Control （QC） schemes was researched. The main differences between the two schemes are cloud detection, O-B （brightness temperature difference between observation and model simulation） check and thinning. To evaluate the impact of the two QC schemes on GRAPES, a typhoon case study and cycle experiments were conducted. In the typhoon case study, two experiments were conducted using both the new and old QC schemes. The results show that outliers are removed in the new QC while they exist in the old QC. The analysis and the model forecast are subsequently generated after assimilating data from the two QC schemes. The model-predicted steering flows more southward with the new QC scheme, and as a result, the forecast track in the experiments is more southward, i.e., closer to the best track than the old scheme. In addition to the case study, four impact cycle experiments were conducted for 25-day periods. The results show that the new QC scheme removed nearly all the biases whereas the old scheme could not. Furthermore, the mean and standard deviation of analysis increments with the new scheme is much smaller than those of O-B. In contrast, the old scheme values are either slightly smaller or the same. Verifications indicate that forecast skill is improved after applying the new scheme. The largest improvements are found in the Southern Hemisphere. According to the results above, MWTS with the new QC scheme can improve the GRAPES forecast.

关键词： FY-3 MWTS typhoon GRAPES

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Liquid Water Path Retrieval Using the Lowest Frequency Channels of Fengyun-3C Microwave Radiation Imager(MWRI)

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Journal of Meteorological Research 2017年第6期31卷 1109-1122页

作者： Fei TANG xiaolei zou Joint Center of Data Assimilation for Research and Application College of Atmospheric ScienceNanjing University of Information Science &Technology State Key Laboratory of Severe Weather Chinese Academy of Meteorological SciencesChina Meteorological Administration Earth System Science Interdisciplinary Center University of Maryland College Park

The Microwave Radiation Imager （MWRI） on board Chinese Fengyun-3 （FY-3） satellites provides measurements at 10.65, 18.7, 23.8, 36.5, and 89.0 GHz with both horizontal and vertical polarization channels. Brightness temperature measurements of those channels with their central frequencies higher than 19 GHz from satellite-based microwave imager radiometers had traditionally been used to retrieve cloud liquid water path （LWP） over ocean. The results show that the lowest frequency channels are the most appropriate for retrieving LWP when its values are large. Therefore, a modified LWP retrieval algorithm is developed for retrieving LWP of different magnitudes involving not only the high frequency channels but also the lowest frequency channels of FY-3 MWRI. The theoretical estimates of the LWP retrieval errors are between 0.11 and 0.06 mm for 10.65- and 18.7-GHz channels and between 0.02 and 0.04 mm for 36.5- and 89.0-GHz channels. It is also shown that the brightness temperature observations at 10.65 GHz can be utilized to better retrieve the LWP greater than 3 mm in the eyewall region of Super Typhoon Neoguri （2014）. The spiral structure of clouds within and around Typhoon Neoguri can be well captured by combining the LWP retrievals from different frequency channels.

关键词： microwave remote sensing Fengyun-3C Microwave Radiation Imager （MWRI） liquid water path （LWP） retrieval

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Quality control of specific humidity from surface stations based on EOF and FFT—— Case study

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Frontiers of Earth Science 2015年第3期9卷 381-393页

作者： Hong ZHAO xiaolei zou Zhengkun QINl Center of Data Assimilation for Research and Application Nanjing University of Information Science & Technology Nanjing 210044 China Vlaryland College Park MD 20740-3-823 USA

Comparisons between observations and back- ground fields indicate that amplitude and phase differences in oscillations result in a non-Gaussian distribution in observation minus background vectors （OMB）. Empirical Orthogonal Function （EOF） quality control （QC） and Fast Fourier Transform （FFT） quality control are proposed from the perspective of data assimilation and are applied to the surface specific humidity from ground-based stations. The QC results indicate that the standard deviation between observations and background is reduced effectively, and the frequency distribution for the observation increment is closer to a normal distribution. The specific humidity outliers occur primarily in mountainous and coastal regions. Comparing the two QC methods, it is found that the EOF QC performs better than the FFT QC as it can keep large scale of fluctuation information from the original field, preventing these waves from entering into the residual field and being removed by the QC process.

关键词： specific humidity quality control EOF FFT

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