Intraseasonal variations of water vapor and cirrus clouds in the tropical upper troposphere
Intraseasonal variations of water vapor and cirrus clouds in the tropical upper troposphere
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DOI：
10.1029/2003jd004314
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发表时间：
2004-06
影响因子：
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通讯作者：
N. Eguchi;M. Shiotani
中科院分区：
文献类型：
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作者：
N. Eguchi;M. Shiotani
[1]利用UARS卫星上的微波临边探测器（MLS）和低温临边阵列标准具谱仪（CLAES）的资料，研究了热带对流层上层水汽和卷云季节内振荡（ISO）的时空变化。利用1991-1993年两个冬季（1991-1993年）的20-80天带通滤波资料，分析了基于五个ISO事件的复合湿度场和气象场。在215和146 hPa，对流系统上空存在着频繁出现卷云的湿异常，并从印度洋向东移动到中太平洋，表明对流活动的直接影响达到了这一水平。在100 hPa，然而，水汽场似乎间接影响对流活动通过动力学响应对流加热。在ISO的发展阶段附近的印度洋和成熟到衰减阶段附近的东太平洋观测到干异常。在对流系统以东的寒冷地区经常发现卷云。对流层顶附近的这些结构与对流加热、赤道冷异常和副热带反气旋涡旋的Kelvin波和Rossby波东移响应密切相关。在这两个环流之间，当印度洋和西太平洋上的对流系统发展时，通过赤道冷区吹来的东风可能通过卷云的形成引起脱水。随着北方环流的加强，热带干空气被输送到副热带太平洋，最终到达赤道东太平洋。结果表明，由Kelvin-Rossby波耦合结构引起的温度和气流变化对热带和副热带对流层顶的空气脱水起着重要作用。
[1] Space-time variations of tropical upper tropospheric water vapor and cirrus clouds associated with the intraseasonal oscillation (ISO) are investigated using data from the Microwave Limb Sounder (MLS) and the Cryogenic Limb Array Etalon Spectrometer (CLAES) on board the Upper Atmosphere Research Satellite (UARS). Composite moisture and meteorological fields based on five ISO events selected in two boreal winters (1991–1993) are analyzed using 20–80 day band-pass-filtered data. At 215 and 146 hPa, wet anomalies with frequent appearance of cirrus clouds exist over the convective system and move eastward from the Indian Ocean to the central Pacific, suggesting a direct effect of convective activity up to this level. At 100 hPa, however, the moisture field seems to be indirectly affected by convective activity through the dynamical response to the convective heating. Dry anomalies are observed over the Indian Ocean around the developing stage and over the eastern Pacific around the mature-to-decaying stage of the ISO. Cirrus clouds are frequently found over the cold region located to the east of the convective system. These structures around the tropopause level are closely related to the eastward moving Kelvin and Rossby wave responses to the convective heating with the equatorial cold anomaly and with the subtropical anticyclonic gyres. Between the two gyres the easterly wind blowing through the equatorial cold region may cause dehydration through cirrus formation when the convective system develops over the Indian Ocean and the western Pacific. As the northern gyre intensifies, tropical dry air is transported to the subtropical Pacific and eventually to the equatorial eastern Pacific. It is suggested that the temperature and flow variations due to the coupled Kelvin-Rossby wave structure play an important role in dehydrating air in the tropical and subtropical tropopause region.