描述:

抬升指数(LI)是一种表示自由对流高度以上不稳定能量大小的指数。它表示一个气块 从抬升凝结高度出发，沿湿绝热线上升到500百帕(海拔5500米左右高度)处所具有的 温度被该处实际大气温度所减得到的差值。比如，某一气块沿湿绝热线上升到500百帕 时的理论值为－14°C, 而该处的实际温度为－18°C, 那么抬升指数就是-4。 当差值为负数时，表明气块比其环境温度更暖，因此将会继续上升。该差值的绝对值 越大，出现对流天气的可能性也越大。差值为正数时，表示大气层结稳定。

值得注意的是，中国气象学家定义的抬升指数和上面的定义正好相反，他们用一个气块 沿湿绝热线上升到500百帕处所具有的温度减去该处实际大气温度得到的差值定义抬升 指数(大气科学辞典，P603)。因此获得的抬升指数值和我们此处的抬升指数值符号正好 相反。

抬升指数

天气现象

>0

不可能出现雷雨天气

0－ -3

可能出现雷雨天气

-3 - -5

很可能出现雷雨天气

-5 - -7

强对流(雷雨)天气

<-7

大气极端不稳定，强对流天气

MERRA:

The MERRA time period covers the modern era of remotely sensed data, from 1979 through the present, and the special focus of the atmospheric assimilation is the hydrological cycle. Previous long-term reanalyses of the Earth's climate had high levels of uncertainty in precipitation and inter-annual variability. The GEOS-5 data assimilation system used for MERRA implements Incremental Analysis Updates (IAU) to slowly adjust the model states toward the observed state. The water cycle benefits as unrealistic spin down is minimized. In addition, the model physical parameterizations have been tested and evaluated in a data assimilation context, which also reduces the shock of adjusting the model system. Land surface processes are modeled with the state-of-the-art GEOS-5 Catchment hydrology land surface model. MERRA thus makes significant advances in the representation of the water cycle in reanalyses.

Reanalyse:

Retrospective-analyses (or reanalyses) integrate a variety of observing systems with numerical models to produce a temporally and spatially consistent synthesis of observations and analyses of variables not easily observed. The breadth of variables, as well as observational influence, make reanalyses ideal for investigating climate variability. The Modern Era-Retrospective Analysis for Research and Applications supports NASA's Earth science objectives, by applying the state-of-the-art GEOS-5 data assimilation system that includes many modern observing systems (such as EOS) in a climate framework.