垂直积分Vint函数的加权的问题

秫彡

Vint函数的质量加权的权重系数是什么，是2个lev的气压差还是其他方法确定的

river

去grads官网看下函数介绍就知道了

vint

vint(psexpr,expr,top)

This function performs a mass-weighted vertical integral in mb pressure coordinates. The three arguments to vint are:

psexpr   a GrADS expression for the surface pressure, in mb, which bounds the integral on the bottom.
expr     a GrADS expression representing the quantity to be integrated.
top      the bounding top pressure, in mb. This value must be a constant and cannot be provided as an expression.

The calculation is a sum of the mass-weighted layers:

f/g * sum(expr * Delta(level))
The bounds of the integration are the surface pressure and the indicated top value. The scale factors are f=100 and g=9.8. The summation is done for each layer present that is between the bounds. The layers are determined by the Z levels of the default file. Each layer is considered to be from the midpoints between the levels actually present, and is assumed to have the same value throughout the layer, namely the value of the gridpoint at the middle of the layer.

Usage Notes

The summation is done using the Z levels from the default file, so it is important that the default file have the same Z dimension coordinates as expr.
Data levels below and above the bounds of the summation are ignored.
The Z dimension in world-coordinate units is assumed to be pressure values given in millibars (mb). The units of g are such that when the expression integrated is specific humidity (q) in units of g/g, the result is kg of water per square meter, or precipitable water in mm.
It is usually a good idea to make the top pressure value to be at the top of a layer, which is midway between grid points. For example, if the default file (and the data) have pressure levels of ...,500,400,300,250,... then a good value for top might be 275, the value at the top of the layer that extends from 350 to 275 mb.
The vint function operates only in an X-Y varying dimension environment.
Be sure the units of the surface pressure (argument 1) are in millibars (mb).
Examples

1. This expression will integrate specific humidity to obtain precipitable water, in mm:

vint(ps,q,275)
2. This is an artificial example that demonstrates a vertical integration from a fixed lower bound of 1000mb to the top of the atmosphere, and integrating a field of all 1's. This gives an answer of 10204.1 (or 100000/9.8) which is the mass of air (in kg) of a 1 meter squared column when the surface pressure is 1 bar and the accelleration due to gravity is assumed to be exactly 9.8m/sec**2 over the entire column.

vint(const(ps,1000),const(t,1),0)

自导自演

river 发表于 2015-4-17 17:59
去grads官网看下函数介绍就知道了

vint

想请教一下，vint函数中，100/9.8到底是啥意思

river

自导自演 发表于 2016-12-6 15:07
想请教一下，vint函数中，100/9.8到底是啥意思

你去看一下天原书上大型降水天气过程中的降水率得概念，9.8好理解，那个100我现在也搞不清楚了。你研究一下告诉我吧

自导自演

river 发表于 2016-12-7 12:09
你去看一下天原书上大型降水天气过程中的降水率得概念，9.8好理解，那个100我现在也搞不清楚了。你研究一 ...

好的，谢谢river

自导自演

river 发表于 2016-12-7 12:09
你去看一下天原书上大型降水天气过程中的降水率得概念，9.8好理解，那个100我现在也搞不清楚了。你研究一 ...

有人说，100是计算时又把hPa换算成pa

river

自导自演 发表于 2016-12-7 14:45
有人说，100是计算时又把hPa换算成pa

那应该是的，我记得是用来单位换算的

hactwyw

scale应该就是百帕向帕的转换

Seaside

我想问下 这个vint函数积分是从地面积到高层吗 如果fortran计算的话 是不是就是相邻两层气压平均值乘气压，那这样的话到底算是地面积分到高层还是高层积分到地面呢，如果地面积分到高层dp不就是负值了？