对流性降水云微波辐射特性
Radiative Characteristics of Convective Precipitating Cloud
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摘要: 结合MM5模式和三维微波辐射传输模式, 对2003年7月9日宜昌地区一次典型的中尺度降水中心的对流性降水云微波辐射特性进行研究。结果表明:MM5模式模拟的降水量和落区与实况一致,模拟的水凝物廓线也与TMI反演值接近,85.5 GHz通道辐射亮温与TMI实测情况相近。85.5 GHz通道亮温与地面雨强相关性很弱, 受云中云冰和雪花的散射降温作用显著, 由于其他粒子的综合作用以及斜角观测造成的位置偏移, 霰粒子对该通道亮温散射作用不明显。19.35 GHz通道亮温随雨强增加先升温后降温; 与霰粒子含量表现出明显的负相关关系。37.0 GHz通道亮温随雨强的增加而降温, 雨强大于20 mm/h后达到饱和, 主要受雨水降温作用影响。倾斜观测比天顶垂直观测产生更低的亮温低值中心, 且频率越高, 低值中心的偏移越严重。Abstract: Radiative characteristics of convective precipitating cloud can be used for the classification of convective/stratiform precipitation and for the algorithm to retrieval the rain rate from brightness temperature observed by satellite remote sensors. The typical convective cloud system in Yichang area on 9 July 2003 is simulated with MM5 model and its upwelling radiative brightness temperature is simulated with Monte-Carlo 3D microwave radiative transfer model. The columnar precipitation simulated by MM5 model shows consilient with that observed by rain gauges. As for the cloud microphysical particles, it is found that except for the cloud ice, the contents of the cloud water, precipitable water and precipitable ice particles from the MM5 are nearly equivalent to that retrieved from TMI data. The simulated Tb85V from M-C model also indicates similar distribution with the observed by TMI. Tb85 is sensitive primarily to the precipitated ice and snow content in clouds. The weak correction between Tb85 and the surface rain rate is found. Given the rain rate less than about 5 mm per hour in this case, Tb19 rises since the rain rate increases. However it descends with the rain rate increasing while the rain rate is over 5 mm per hour. Because of the notable intercorrelation between Tb19 and graupel content, it can be regarded as the indicator of surface rain rate in the strong convective center, at least as the estimator of columnar precipitated water content at upper layers. The feeble correlation between Tb85 and graupel columnar content happens because the upwelling Tb85 is synthetically affected by the various hydrometers such as the emission from cloud water and the scattering from ice particles, in addition the shift caused by oblique FOV. Tb37 has obvious correlation with the surface rain rate when it is less than 20 mm per hour and is saturated when the rain rate is over 20 mm per hour. Cloud water and precipitated rain in the convective cloud play roles on Tb37. The Tb at each channel shows the synthetical results of tilted cloud cell or oblique FOV. The higher frequency, the lower Tb values show and the more replacement happens due to the oblique FOV. Tb85 observed at 52.8° angle is even 15 K less than that received at zenith, and the shift can reach 25 km as well as the title cloud cell.
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Key words:
- MM5;
- radiation transfer model;
- radiative characteristics
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图 1 2003年7月9日20:05模拟区域上TM1的实测 (a) 和模式模拟的85.5 GHz (b) 垂直极化通道亮温
(单位: K; 图a中箭头为TM1的运行轨道方向, 图b中箭头为模拟的轨道方向)
Fig. 1 Brigluness temperature at 85:5 GHz V-polarized channel observed by TM1 and simulated by Monte-Carlo radiative transfer model at 20:05 on 9 July 2003
( unit: K; the arrow in Fig.a is the observed orbital direction of TM1, the arrow in Fig.b is the simmlated orbital direction of Monte-rarlo)
图 2 2003年7月9日 16:00 Domain3模拟的整个区域 (观测角度设为52.8°)
(a) 云水、雨水和霰的总和垂直积分含量 (阴影部分) 及云冰和雪花含量的总和垂直积分含量 (等值线部分, 单位: kg·m-2), (b) 地面降水率 (阴影部分, 单位: mm/h) 及19.35 GHz通道的垂直极化辐射亮温 (等值线部分, 单位: K), (c) 85.5 GHz通道的垂直极化辐射亮温(单位: K), (d) 37.0 GHz通道的辐射亮温 (单位: K)
Fig. 2 Simulated area with 52.8° nadir scan view at 16:00 9 July 2003 on Domain3
(a) the columnar content of combined cloud water, cloud rain and graupel (shaded) and the columnar content of combined cloud ice and snow (contour, unit: kg·m-2), (b) rain rate (shaded, unit: mm/h) and simulated brightness temperature at 19.35 GHz V-polarized channel (contour, unit: K), (c) the simulated brightness temperaiure at 85.5 GHz V-polarized channel (unit: K), (d) the simulated brightness temperature at 19.35 GHz V-polarized channel (unit: K)
图 3 2003年7月9日16:00 y=32垂直剖面上云水、雨水、霰、冰晶和雪花含量 (单位:g·m-3) 的分布以及地面雨量 (单位: mm/h) 、0°和52.8°观测角时 85.5, 37.0, 19.35 GHz 3 个通道的垂直极化亮温 Tb85, Tb37, Tbl9 (单位: K)
Fig. 3 The y-z cross section of the contents of cloud water, cloud rain, graupel, cloud ice snow (unit: g·m-3) and the rain rate (unit: mm/h) with the brightness temperatures at 85.5, 37.0 GHz and 19.35 GHz Tb85, Tb37, Tbl9 V-polarized channels at 0°and 52.8° nadir scan view respectively (unit: K)
表 1 MM5模式参数化设置
Table 1 The parameteration schemes on Domains within MM5 model
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