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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 = k_{1} * P_{d}/T + k_{2} * P_{w}/T + k_{3} * P_{w}/T^{2}

where P_{d} is the partial pressure of dry air and where P_{w}
is the partial pressure of water vapor. Using equation of state, the formula can be
rewritten as n = n_{d} + n_{w}, where

n_{d} = k_{1} * R/M_{d} ρ, and
n_{w} = (k_{2} - k_{1} M_{w}/M_{d}) * P_{w}/T +
k_{3} * P_{w}/T^{2}.

Here ρ is air density, R — universal
gas constants, M_{w} and M_{d} are molar mass of water vapor and dry air
respectively.

Then zenith path delay can be determined as
τ_{w} = ∫^{∞}
_{0}
**(n**_{w}(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 P_{w}(h) and T(h) at nodes of
0.25° x 0.3125° x 72 x 3_{h} 4D grid. The zenith path delay
was determined by numerical integration of n_{w}(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