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

Abstract

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, version 2.2.4, 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 to 1.0 K. The relationships between channels 2, 4, and 5 biases and scan angle are symmetrical about the nadir. The latitude-dependent 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.

概要

本研究使用了2011至2017连续7年的NOAA-18 微波湿度计观测亮温资料, 欧洲中期天气预报中心再分析资料, 以及由美国国家海洋和大气管理局研发的云水路径和冰水路径产品, 探讨了微波湿度计各通道观测资料与模拟资料的偏差与冰水路径值的关系以及云水路径值对这一关系的影响. MHS窗区通道扫描角偏差的变化范围是-1.7K至1.0K, 通道2、4、5的扫描角偏差关于星下点对称. MHS窗区通道的纬度带偏差的变化范围为0至7K, 非窗区通道的纬度带偏差随探测高度的增高而增大. 在去除通道的扫描角偏差和纬度带偏差后, MHS观测亮温与模拟亮温差值的全球洋面分布不再具有系统性的冷暖误差, 此差值随冰水路径值得增大而增大, 且这一关系的显著性与云水路径值正相关.