65th IHC Booklet/Program (pdf - 4.9MB) - Office of the Federal ...

Direct Interpretation of COSMIC Refractivity Data in the Tropical Cyclone Environment
Christopher M. Hill, Patrick J. Fitzpatrick, and Yee Lau
(hillcm@gri.msstate.edu)
Geosystems Research Institute, Mississippi State University, Stennis Space Center, MS
This study continues to explore the utility of the Constellation Observing System for
Meteorology, Ionosphere, and Climate (COSMIC) in measuring moisture in the vicinity of
tropical cyclones. From a formula relating GPS signal refractivity to temperature, pressure, and
vapor pressure (Smith and Weintraub 1953, Kursinski et al. 1995), especially high (low) values
of refractivity at a known pressure level correspond to high (low) vapor pressure in a relatively
high temperature environment. The implication is that a relative measure of moisture can be
attained with only refractivity at a known pressure level, and without specific knowledge of
temperature, in a tropical environment. The relation of refractivity to tropospheric
thermodynamics further yields a critical value of refractivity below which water vapor saturation
– and therefore clouds – cannot exist at a known pressure level.
The above findings are applied in the evaluation of a June-September climatology of COSMIC
refractivity over the tropical and subtropical eastern Atlantic Ocean, as well as in the evaluation
of individual COSMIC refractivity profiles with varying proximity to select Atlantic tropical
cyclones. Nomograms relating refractivity to pressure and temperature have been constructed to
assist in the determination of moisture content for given values of refractivity and pressure.
References:
Kursinski, E. R., G. A. Hajj, K. R. Hardy, L. J. Romans, and J. T. Schofield, 1995: Observing
tropospheric water vapor by radio occultation using the Global Positioning System, Geophys.
Res. Lett., 22, 2365–2368, doi:10.1029/95GL02127.
Smith, E. K., and S. Weintraub, 1953: The constants in the equation for atmospheric refractivity
index at radio frequencies. Journal of Research of the National Bureau of Standards, Vol. 50, p.
39-41.
Poster Session – Page 7