# How to calculate water vapor flux divergence from temperature, relative humidity, u wind and v wind?

I have temperature, u wind, v wind and relative humidity. I am wondering to calculate water vapor flux divergence and convergence.

Would anybody kindly help to find our a solution for this?

The formula for moisture flux is $$q\vec{V}$$ where $q$ is the water vapor mixing ratio, which can be found using mixhum_ptr and $\vec{V}$ is the velocity.

Therefore the divergence of the moisture flux must be $$\nabla{\dot{}q\vec{V}}=\frac{\partial(qu)}{\partial x}+\frac{\partial(qv)}{\partial y}+\frac{\partial(qw)}{\partial z}$$ $$\approx\frac{\delta(qu)}{\delta x}+\frac{\delta(qv)}{\delta y}+\frac{\delta(qw)}{\delta z}$$

which is computable if you have gridded data.

For example, you could compute this by setting $$qu=q\ast u$$ $$qv=q\ast v$$ $$qfluxDiv=uv2dv\_cfd(qu,qv,lat,lon,opt)$$ Use uv2dv_cfd per http://www.ncl.ucar.edu/Document/Functions/Built-in/uv2dv_cfd.shtml

Note: If you wanted the turbulent moisture flux, you would need to subtract $\nabla{\dot{}\bar{\vec{V}}\bar{q}}$ from your answer.