Annual and diurnal variation of precipitable water over California and Nevada

A seven year (2003-2009) data set of precipitable water (integrated water vapor) values obtained from more than 500 Global Positioning System (GPS) sites has been used to examine diurnal variation in precipitable water over California and Nevada. Most sites show a clear diurnal variation, with small values near the coast increasing rapidly inland. The temporal variation is used to fit a sinusoidal curve to the data for each site; the maximum of the sinusoid gives the peak local time of daily cycle. The peak of the diurnal cycle generally occurs earlier in sites near the ocean and other water bodies, and later away, suggesting that the peak in the water vapor diurnal cycle may be determined by peak heating of adjacent water bodies, and then modified by the travel time of sea breezes from the water to the land.