Resolving SSM/I-ship radar rainfall discrepancies from AIP-3

The third algorithm intercomparison project （AIP-3） involved rain estimates from more than 50 satellite rainfall algorithms and ground radar measurements within the Intensive Flux Array （IFA） over the equatorial western Pacific warm pool region during the Tropical Ocean Global Atmosphere coupled Ocean-Atmosphere Response Experiment （TOGA COARE）. Early results indicated that there was a sys- tematic bias between rainrates from satellite passive microwave and ground radar measurements. The mean rainrate from radar measurements is about 50% underestimated compared to that from passive microwave-based retrieval algorithms. This paper is designed to analyze rain patterns from the Florida State University rain retrieval algorithm and radar measurements to understand physically the rain discrep- ancies. Results show that there is a clear range-dependent bias associated with the radar measurements. However, this range-dependent systematical bias is almost eliminated with the corrected radar rainrates. Results suggest that the effects from radar attenuation correction, calibration and beam filling are the major sources of rain discrepancies. This study demonstrates that rain retrievals based on satellite mea- surements from passive microwave radiometers such as the Special Sensor of Microwave Imager （SSM/I） are reliable, while rain estimates from ground radar measurements are correctable.     

洋面水汽的微波SSM/I资料反演试验

结合1987年7月华北一次降水过程,利用SSM/I微波资料反演了渤海湾洋面大气柱水汽含量。反演结果与探空资料以及天气实况的对比分析表明,洋面大气柱水汽总含量的SSM/I微波反演结果与探空观测符合得较好,而且能够较好地反映非阵性降水的空间分布和时间变化。     

SSM/I资料反演大范围地表湿度试验

利用SSM/ I遥感数据, 结合2002年汛期“973”外场观测资料及T106资料, 借助微波辐射传输正演模型, 通过物理反演原理提取SSM/ I低频19 GHz通道像元平均地表微波比辐射率, 然后利用地表微波辐射模型, 估算SSM/ I像元的地表湿度信息。以2002年8月中旬发生在长江流域的暴雨天气过程为例, 将反演得到的地表湿度信息与地面观测到的降水信息进行对比分析, 并与地面的洪涝特征进行对比分析, 得到了与地面降水观测结果较为一致的对比结果。     

A comparison of SSM/I and TOVS column water vapor data over the global oceans

Summary This paper presents a comparison of column water vapor (CWV) information derived from both infrared measurements as part of the TIROS-N Operational Vertical Sounder (TOVS) and Special Sensor Microwave/Imager (SSM/I) in an attempt to assess the relative merits of each kind of data. From the analyses presented in this paper, it appears that both types of satellite data closely reproduce the bulk climatological relationships introduced in earlier studies using different data. This includes both the bulk relationship between CWV and the sea surface temperature and the annual variation of CWV over the world's oceans. The TOVS water vapor data tends to be systematically smaller than the SSM/I data and when averaged over the ocean covered regions of the globe this difference is between 2–3 kgm^–2. Using a cloud liquid water threshold technique to establish clear sky values of SSM/I water vapor, we conclude that the differences between TOVS and SSM/I are largely a result of the clear sky bias in TOVS sampling except in the subsidence regions of the subtropics. The clear sky bias is considerably smaller than previously reported and we attribute this improvement to the new physical retrieval scheme implemented by NOAA NESDIS. While there is considerable agreement between the two types of satellite data, there are also important differences. In regions where there is drying associated with large scale subsidence of the atmosphere, the TOVS CWV's are too moist relative to both radiosonde and SSM/I data and this difference may exceed 10 kgm^–2. The explanation for this difference lies in the limitations of infrared radiative transfer. By contrast, in regions of deep convection, such as in the ITCZ, TOVS CWV is systematically lower than the SSM/I CWV. Both TOVS and SSM/I data demonstrate similar kinds of gross effects of large scale circulation on the water vapor except in these subsidence regions where TOVS data leads to an under-prediction of the effects of subsidence drying.With 11 Figures     

Atmospheric water balance in Typhoon Nina as determined from SSM/I satellite date

Summary Precipitation, cloud water amount and phase, and water vapor amount are very important parameters in understanding the development of typhoons and their influence on the atmosphere and ocean. In this paper, we investigate the atmospheric water balance of Typhoon Nina, which formed near (5°N, 160°E) on November 18, 1987 and moved northwestward during its development. Water vapor path, liquid water path, ice index, and precipitation amount are determined in the vicinity of the typhoon using data from the SSM/I (Special Sensor Microwave/Imager). The water balance of the, typhoon cloud is then examined during its different development stages. An ice index is derived using SSM/I data that is used to investigate the overall ratio of ice/liquid water change of the typhoon during its development. By comparing the ice/water ratio of different mesoscale convective cells in the typhoon, attempts are made to interpret the different cloud structures and development stages of individual mesoscale cloud cells relative to their position from the typhoon center.It is found that the atmospheric water budget in the typhoon is mainly balanced by horizontal transport of water vapor into the region, evaporation from the ocean and precipitation. Of the two source terms, horizontal transport plays the major role with a contribution of more than 65% in all storm stages for 1° radial area or larger. In addition, the horizontal transport of water vapor seems to occur through several bands instead of uniform convergence. Mesoscale convective cells, which may consist of several cumulonimbus clouds in each, develop in the bands, with convectively more active cells occurring upwind and the dissipating one downwind. It it also found that the maximum latent heat release precedes the maximum storm intensity.With 15 Figures     

The Capability of Atmospheric Profile Retrieval from Satellite High Resolution Infrared Sounder Radiances

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微波湿度计资料在GRAPES模式中偏差订正方法研究

根据微波湿度计MHS(Microwave Humidity Sounder)辐射率资料及GRAPES(Global/Regional Assimilation and Pr Ediction System)模式的特点,建立适用于MHS资料的偏差订正系统,该系统包括扫描和气团偏差订正,其中气团偏差订正考虑水汽资料的特性,采用三种不同预报因子组合的方案。偏差订正结果表明:MHS各个通道的扫描偏差表现出不同特征;偏差订正后观测残差基本服从均值为零的高斯分布,且观测残差的均值有所降低并随时间变化平稳;三种气团偏差订正方案都有明显的订正效果,其中方案三的订正效果最佳。     

Rain rate estimation from a synergetic use of SSM/I, AVHRR and meso-scale numerical model data

Summary In this paper a retrieval technique for estimating rainfall rates is introduced. The novel feature of this technique is the combination of two satellite radiometers — the Special Sensor Microwave/Imager (SSM/I) and the Advanced Very High-Resolution Radiometer (AVHRR) — with mesoscale weather prediction model data. This offers an adjustment of the model atmospheres to reality which is necessary for calculating brightness temperatures that can be compared with microwave satellite measurements.In sensitivity studies it was found that the estimation of precipitation is determined to a high degree by the particle size distribution of rain and snow, especially by the size distribution of solid hydrometeors. These studies also reveal the influence of the knowledge of the correct cloud coverage inside a SSM/I pixel and the importance of using a realistic temperature profile instead of using standard atmospheres.The retrieval technique is based on radiative transfer calculations using the model of Kummerow et al. (1989). The algorithm consists of two parts: First Guess (FG) brightness temperatures for the SSM/I frequencies are generated as a function of the cloud top height and the cloud coverage, derived from AVHRR data and predictions from a meso-scale model. The rainfall rate of different types of clouds containing raindrops, ice particles and coexisting ice and water hydrometeors is then calculated as a function of the cloud top height. As an example, a strong convective rain event over the western part of Europe and over the Alps is taken to evaluate the performance of this technique. Good agreement with radar data from the German Weather Service was achieved. Compared to statistical rainfall algorithms, the current algorithm shows a better performance of detecting rainfall areas.With 12 Figures     

Sensitivity of retrieved atmospheric profiles from infrared radiances to physical and statistical parameters of the data assimilation system

Abstract

The direct assimilation of satellite radiances is now operational in a few forecast centres, providing global temperature (T) and moisture (Q) information. The critical parameters which influence the quality of the resulting analysis are mainly the selection of channels, the respective errors of the background field and radiance observations, and the quality of the radiative transfer model. These various aspects are studied from sensitivity experiments based on 1‐D variational assimilations using the ensemble of 19 infrared channels (HIRS) of the NOAA‐14 satellite.

It is shown that significant improvements in the retrievals would be obtained if the radiance observation error (measurement plus radiative transfer), currently estimated to be about equal to that of the background (in radiance units), were decreased. This could in principle be achieved by improving the forward radiative transfer model (RTM). Two RTMs suitable for radiance assimilation are compared in terms of analyzed increments, Jacobians, brightness temperature and equivalent background error. Important differences are noted for all of these interrelated measures. The existence of air‐mass dependent biases of fast radiative transfer models of the order of 1.5 K is confirmed in several channels from additional comparison with a line‐by‐line model. The importance of correctly specifying surface emissivity and the effective angle for downward calculations is demonstrated.

The paper also evaluates, in some detail, the impact of uncertainties on the background error covariance matrix. The uncertainty on the skin temperature (TJ error affects mostly the retrieval of that parameter; it has a modest impact on the T and Q profiles in the low troposphere. The uncertainty on the Q‐Q elements has more impact than that on the T‐T elements. Off‐diagonal elements of the background error covariance matrix are very important as they impose smoothness and level‐to‐level consistency, especially for Q retrievals. Finally, T_s‐T correlations, often ignored, could result in significant improvements in the retrieval of temperature at low levels. Research issues are discussed in the conclusion.     

Simultaneous Non-linear Retrieval of Atmospheric Temperature and Absorbing Constituent Profiles from Satellite Infrared Sounder Radiances

Based on Zeng’s theory (1974), a successive linearized form of radiative transfer equation (RTE) is derived for simultaneous retrieval of atmospheric temperature and absorbing constituent profiles from satellite infrared observa-tions. It contains the temperature component weighting function and absorbing constituent (H2O, O3, CH4 etc.) com-ponent weighting functions. All these weighting functions reach maximum at their own “optimum information levels”, and make the remote sensing equations well-conditional. Then the atmospheric profiles are derived by Newton’s non-linear iteration method. Experiments of retrieval from both TIROS-N operational High Resolution Infrared Sounder (HIRS) and the simulated Atmospheric infRared Sounder (AIRS) show an significant improvement.     

A practical approach for the assimilation of cloudy infrared radiances and its evaluation using airs simulated observations

Abstract

A variational estimation procedure for the simultaneous retrieval of cloud parameters and thermodynamic profiles from infrared radiances is proposed. The method is based on a cloud emissivity model which accounts for the frequency dependence of cloud absorption and scattering and possible mixed phase situations. An effective cloud top height and emissivity are assumed. Monte Carlo experiments performed in a 1D‐var assimilation context using simulated Atmospheric Infrared Radiance Sounder (AIRS) observations from 100 channels demonstrate the substantial added value, in theory, of cloudy radiance assimilation as opposed to clear‐channel assimilation. Improved temperature and humidity retrievals are obtained for a broad layer above the cloud as well as below cloud level under partial cloud cover conditions. The impact is most pronounced in broken to overcast situations involving mid‐level clouds. In these situations, the effective cloud top height and emissivity are retrieved with estimated rms errors typically lower than 30 hPa and 3%, respectively. Expected relative errors on the retrieved effective particle size are of the order of 30–50%. The methodology is directly applicable to real hyperspectral infrared data upon inclusion, for local estimation, of the cloud parameters in the Canadian 4D‐var assimilation system.     

对IPCC第六次评估报告中有关干旱变化的解读

政府间气候变化专门委员会（IPCC）于2021年8月发布了第六次评估报告（AR6）自然科学基础卷的决策者摘要,主要对自2013年第五次评估报告（AR5）以来的气候变化科学研究进展进行了系统的评估,并使用新一代气候模式在新的共享社会经济路径情景下对未来气候变化进行了预估。本文基于AR5和AR6相关章节素材,解读了干旱变化的评估结论。     

红外高光谱IASI卫星资料同化对一次大风过程的影响研究

以2019年4月24日发生在辽宁省的一次大风天气过程为例,选取GFS(全球预报系统) 0.25°×0.25°再分析资料,基于WRF模式三维变分同化技术,进行一组IASI资料同化试验,和未同化任何资料的控制试验(CTNL)。通过对比两组试验结果考察IASI资料同化改进数值模式初始场的分析及其后续预报的机制。研究结果表明：经过IASI资料同化的模拟结果质量有很大改善,分析场与背景场相比更靠近观测场;经过云检测之后不同通道使用的观测数目多少不一,资料同化对模拟的改善效果在通道0~800最佳;IASI资料同化对地表10 m风场的预报技巧有显著的提高作用,相比控制试验可以更精准地预报大风天气的区域和强度;IASI同化试验的预报质量高于控制试验且随时间比较稳定。     

包含CO2因子的冠层光合作用简化模型及其关键参数数值敏感分析

利用美国Licor公司生产的Li-6200便携式光合作用测定仪对冬小麦叶片光合作用进行了较为系统的测定研究,在实测资料支持下建立了包含CO2因子的叶片和冠层光合作用模型,验证结果表明,模型具有较高准确性.利用模型对CO2影响参数μ进行数值敏感分析,结果表明:对叶片光合而言,μ=0.83时叶片光合作用模型拟合最好,随μ减小或增大,拟合精度均下降;对冠层光合而言,μ=0.83时模拟光合日总量达到最大值,μ减小或增大,光合日总量均下降.多因子数值分析表明:在辐射值较大的状况下,μ对冠层光合的影响更为显著.     

A simplified scheme of the generalized layered radiative transfer model

In this paper, firstly, a simplified version （SGRTM） of the generalized layered radiative transfer model （GRTM） within the canopy, developed by us, is presented. It reduces the information requirement of inputted sky diffuse radiation, as well as of canopy morphology, and in turn saves computer resources. Results from the SGRTM agree perfectly with those of the GRTM. Secondly, by applying the linear superposition principle of the optics and by using the basic solutions of the GRTM for radiative transfer within the canopy under the condition of assumed zero soil reflectance, two sets of explicit analytical solutions of radiative transfer within the canopy with any soil reflectance magnitude are derived： one for incident diffuse, and the other for direct beam radiation. The explicit analytical solutions need two sets of basic solutions of canopy reflectance and transmittance under zero soil reflectance, run by the model for both diffuse and direct beam radiation. One set of basic solutions is the canopy reflectance αf （written as α1 for direct beam radiation） and transmittance βf （written as β1 for direction beam radiation） with zero soil reflectance for the downward radiation from above the canopy （i.e. sky）, and the other set is the canopy reflectance （αb） and transmittance βb for the upward radiation from below the canopy （i.e., ground）. Under the condition of the same plant architecture in the vertical layers, and the same leaf adaxial and abaxial optical properties in the canopies for the uniform diffuse radiation, the explicit solutions need only one set of basic solutions, because under this condition the two basic solutions are equal, i.e., αf = αb and βf = βb. Using the explicit analytical solutions, the fractions of any kind of incident solar radiation reflected from （defined as surface albedo, or canopy reflectance）, transmitted through （defined as canopy transmittance）, and absorbed by （defined as canopy absorptance） the canopy and other properties per