Wet zenith path delay of radio waves propagation through the neutral atmosphere

Zenith wet path delay in the neutral atmosphere has been computed at the global grid 0.25° x 0.3125° grid using numerical weather model GEOS-57 developed at the Global Modeling and Assimilation Office of the NASA GSFC. Wet zenith delay is determined the following way. The refractivity index of wet air at temperature T:  

n = k1 * Pd/T + k2 * Pw/T + k3 * Pw/T2

where Pd is the partial pressure of dry air and where Pw is the partial pressure of water vapor. Using equation of state, the formula can be rewritten as n = nd + nw, where

nd = k1 * R/Md ρ,    and    nw = (k2 - k1 Mw/Md) * Pw/T + k3 * Pw/T2.

Here ρ is air density, R — universal gas constants, Mw and Md are molar mass of water vapor and dry air respectively.
Then zenith path delay can be determined as   τw = 0 (nw(h) - 1) dh, where integration is over the height h along the plumb line from the surface to the top of the atmosphere.

Time series of zenith path delay on a global grid for 2012 with 3 hourly resolution

The output of the numerical weather model GEOS-57 has been processed to determine Pw(h) and T(h) at nodes of 0.25° x 0.3125° x 72 x 3h 4D grid. The zenith path delay was determined by numerical integration of nw(h). Results of integration in HEB-format are available for downloading here (2920 files, 3.3Mb per epoch, 9.8 Gb/yr).

The movie of changes in zenith path delay at a global grid over 2012

The time series of zenith wet path delay from GEOS-57 can be visualized as a movie (4:52 duration, mpg format, 34MB).

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This page was prepared by Leonid Petrov ()
Last update: 2013.06.26_22:08:05