雨率

什么是降水?

沉淀是一种关键的水文和气候变量,包括液体(雨)和固体(雪和冰)形式。当通过水蒸气的冷凝形成的颗粒变得足够重以落在重力的力下时,发生沉淀。沉淀可以在大气中的任何垂直水平下测量,但它是在地球表面落下的量,这对人们最相关。在RSS的情况下,我们从微波辐射计的海洋上汲取表面雨率的估计。

Measurement of Precipitation

由于其对人类文明的重要性,已经开发了许多技术用于遥感降水。遥感尤为重要,对于在庞大的海洋地区和偏远地区存在的偏远地区的沉淀尤为重要。遥感技术包括两个一般类别,主动遥感和被动遥感。主动遥感涉及传输电磁辐射的脉冲,并测量从目标反弹的辐射(在这种情况下雨水落下)。天气雷达是有源传感器的一个例子。被动遥感只是测量传入的辐射,就像没有闪光灯的相机。微波和红外成像器是被动传感器的示例。

被动遥感的公关ecipitation is possible at microwave and infrared wavelengths. Microwave radiation has wavelengths around 1 cm, while infrared radiation has wavelengths about 1000 times shorter. For this reason, microwave measurements can see deep inside the cloud, while infrared measurements see just the cloud top. It also means that microwave measurements have a lower spatial resolution compared to infrared. The spatial resolution of a microwave sensor is improved by placing it in lower orbit. Microwave sensors are typically placed on satellites in a low earth orbit (350-850 km), while infrared sensors are typically placed in a geostationary orbit (36,000 km).

The physical basis for retrieving precipitation from passive microwave measurements depends on distinguishing the radiation coming from Earth’s surface with the radiation coming from precipitation. This is more difficult to do over land, so we provide estimates over the ocean only. The microwave emission from the ocean surface is strongly polarized, while the emission from rain drops is unpolarized. Thus, precipitation can be accurately distinguished from the underlying ocean surface using measurements of the vertically and horizontally polarized radiation. Liquid water produces a much stronger signal than ice, so we provide estimates of rain rate only.

Time Scales of Precipitation

Precipitation exhibits variability across a wide range of time scales. Capturing precipitation variability on time scales less than one day requires measurements from as many sensors as possible. Capturing the variability on time scales longer than one year requires continuous records from consistently-calibrated sensors. Specific atmospheric phenomena are associated with each of the time scales of precipitation variability, and examples are discussed below. These examples illustrate how different datasets can be used to study different phenomena. The analysis shown here is for the time period 1998-2012.

On time scales of less than one day is the diurnal cycle of precipitation. Figure 1 shows the hourly precipitation anomaly from the daily average. Over the ocean, precipitation is generally at a maximum in the early morning local time. This is in contrast to over land, where the maximum precipitation is generally associated with the heating of the day.

Figure 1.  Daily precipitation anomaly at 6 AM local time (top) and 6 PM local time (bottom).  These images were made from RSS daily TMI.Figure 1.  Daily precipitation anomaly at 6 AM local time (top) and 6 PM local time (bottom).  These images were made from RSS daily TMI.

Figure 1. Daily precipitation anomaly at 6 AM local time (top) and 6 PM local time (bottom). These images were made from RSS daily TMI.

在季节性时间尺度(1-3个月),是Madden-Julian振荡(MJO)。MJO是热带印度和太平洋上的降水异常的传播模式(图2)。MJO阶段由实时多变量MJO指数(RMM)给出。正雨量异常的中心位于相位2中的90°E附近,并通过相6传播至160°E。

Figure 2.  Precipitation anomaly for MJO phases 2 (top), 4 (center), and 6 (bottom).  These images were made from RSS daily merged rain rate.Figure 2.  Precipitation anomaly for MJO phases 2 (top), 4 (center), and 6 (bottom).  These images were made from RSS daily merged rain rate.Figure 2.  Precipitation anomaly for MJO phases 2 (top), 4 (center), and 6 (bottom).  These images were made from RSS daily merged rain rate.

图2. MJO阶段2(顶部),4(中心)和6(底部)的降水异常。这些图像是由RSS每日合并的雨率进行的。

在季节性时间尺度上是地球的季风系统。季风是一种季节性逆转的风和降水。图3显示了印度季风的这种逆转。该图描绘了2008年的条件大约一个月在发病后一个月,季风撤离后几周。

Figure 3. Weekly average wind direction and precipitation during the monsoon (top) and after the monsoon (bottom) in 2008.  These images were made from RSS weekly QuikScat winds and RSS weekly SSM/I F13 rain rate.Figure 3. Weekly average wind direction and precipitation during the monsoon (top) and after the monsoon (bottom) in 2008.  These images were made from RSS weekly QuikScat winds and RSS weekly SSM/I F13 rain rate.

图3. 2008年季风(顶部)和季风(底部)后的每周平均风向和降水。这些图像由RSS每周Quikscat风和RSS每周SSM / I F13降雨率。

每年的时间尺度是ElNiño-南方振荡(ENSO)。这是热带太平洋和印度洋的降水和海面温度(SST)模式的全球刻度转变。ElNiño是振荡的温暖阶段,在东太平洋的温暖SST和较重的降水(图4)。LaNiña是凉爽的阶段,其中SST和较重的降水位于远西太平洋(图5)。ENSO相由海洋尼诺索引(ONI)给出,使用±0.5°C的阈值。热带降水中的这些变化远远达到“扎切式”,在人们生活的土地上降水。

Figure 4.  Precipitation (top) and SST (bottom) January anomalies for El Niño conditions.  These images were made from RSS daily merged rain rate and RSS daily OI-SST.Figure 4.  Precipitation (top) and SST (bottom) January anomalies for El Niño conditions.  These images were made from RSS daily merged rain rate and RSS daily OI-SST.

Figure 4. Precipitation (top) and SST (bottom) January anomalies for El Niño conditions. These images were made from RSS daily merged rain rate and RSS daily OI-SST.

Figure 5.  Precipitation (top) and SST (bottom) January anomalies for La Niña conditions.  These images were made from RSS daily merged rain rate and RSS daily OI-SST.Figure 5.  Precipitation (top) and SST (bottom) January anomalies for La Niña conditions.  These images were made from RSS daily merged rain rate and RSS daily OI-SST.

图5.降水(顶部)和SST(底部)1月份的LaNiña条件的异常。这些图像由RSS每日合并的雨率和RSS每日OISST制成。

RSS雨率数据产品

Passive microwave radiometers can only derive rain rate, not precipitation. As part of our radiometer data processing, we determine a rain rate value that is included in the individual satellite gridded binary data files. For more information on the content of these files and data access, see the Mission pages.

所有RSS雨率产品都是使用描述的算法导出的Hilburn和Wentz.(2008). Validation of Version-7 rain rate products is provided by希尔本和史密斯(2012).

乐器 Period of Operation 版本
1Manbetx ,1Manbetx 1987 - present v7.
2018世界杯狗万滚球app 1997 - 2015 v7..1
AMSR-E. 2002年 - 2011年 v7.
AMSR-2 2012 - present V7.2
2019新万博appmanbetⅩ 2003 - present v7.0.1.