Convective Transition Statistics over Tropical Oceans for Climate Model Diagnostics: Observational Baseline
Convective Transition Statistics over Tropical Oceans for Climate Model Diagnostics: Observational Baseline
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DOI：
10.1175/jas-d-17-0287.1
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发表时间：
2018-05-01
影响因子：
3.1
通讯作者：
Neelin, J. David
中科院分区：
文献类型：
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作者：
Kuo, Yi-Hung;Schiro, Kathleen A.;Neelin, J. David
对流转变统计数据描述了柱积分水汽 (CWV) 与降水之间的关系，它是使用卫星和 ARM 站点测量在热带海洋上进行编制的，以量化与对流相关的快速时间尺度上的降水-CWV 关系的温度和分辨率依赖性。在这些时间尺度上，特别是对于降水，必须通过使用各种仪器检查特征并识别高降雨率下的鲁棒行为与仪器灵敏度来解决与观测系统相关的不确定性。这里发现，当 CWV 超过某个临界阈值时，降水量急剧增加对空间分辨率不敏感，随着对流层整体温度的增加，对流发生在较高的 CWV 处，但在较低的柱相对湿度下。以降水为条件的平均对流层温度剖面显示出在很宽的温度范围内垂直相干的结构，再次证实了在定义对流转变统计数据时使用整体温度测量。 CWV和降水的联合概率分布在CWV高于临界值时在低降水时出现峰值概率，在低于和接近临界值时高降水概率迅速下降，并且在空间平均下表现出系统变化。 CWV 的降水量对长达几个小时的时间平均不敏感，但在每日时间尺度上是平滑的。这项工作表明，相对于临界值的CWV可以作为降水的有效预测因子，在热带地区只有微小的地理变化，量化不同时空分辨率下的降水相关统计数据，并为模型比较提供基线，以将这些统计数据用作降水过程的观测约束。
Convective transition statistics, which describe the relation between column-integrated water vapor (CWV) and precipitation, are compiled over tropical oceans using satellite and ARM site measurements to quantify the temperature and resolution dependence of the precipitation-CWV relation at fast time scales relevant to convection. At these time scales, and for precipitation especially, uncertainties associated with observational systems must be addressed by examining features with a variety of instrumentation and identifying robust behaviors versus instrument sensitivity at high rain rates. Here the sharp pickup in precipitation as CWV exceeds a certain critical threshold is found to be insensitive to spatial resolution, with convective onset occurring at higher CWV but at lower column relative humidity as bulk tropospheric temperature increases. Mean tropospheric temperature profiles conditioned on precipitation show vertically coherent structure across a wide range of temperature, reaffirming the use of a bulk temperature measure in defining the convective transition statistics. The joint probability distribution of CWV and precipitation develops a peak probability at low precipitation for CWV above critical, with rapidly decreasing probability of high precipitation below and near critical, and exhibits systematic changes under spatial averaging. The precipitation pickup with CWV is reasonably insensitive to time averaging up to several hours but is smoothed at daily time scales. This work demonstrates that CWV relative to critical serves as an effective predictor of precipitation with only minor geographic variations in the tropics, quantifies precipitation-related statistics subject to different spatial-temporal resolution, and provides a baseline for model comparison to apply these statistics as observational constraints on precipitation processes.