Stable isotope ratios: Hurricane Olivia

The oxygen and hydrogen isotopic compositions of rains from HurricaneOlivia (1994) in the eastern Pacific were measured. The rains werecollected on 24 and 25 September during airplane flights conducted at anelevation of 3 km. Hurricane Olivia peaked in intensity to a category-4storm between the two dates. Isotope ratios of rains from HurricaneOlivia were markedly lower (δ ^sup 18^O = -13.9[per thousand]to -28.8[per thousand]) than that of rain collected from a thunderstormat an elevation of 2.3 km outside the influence of Olivia (δ^sup 18^O = -3.8[per thousand]). A distinct decrease in isotoperatios from the first day to the next (δ ^sup 18^O =-18.4[per thousand] to -21.9[per thousand]) in Hurricane Olivia wasattributed to decreased updraft velocities and outflow aloft. Thisshifted the isotopic water mass balance so that fewer hydrometeors werelifted and more ice descended to flight level. A decrease in the averagedeuterium excess from the first day to the next (d = 15.5 to 7.1[per thousand])was attributed to an increase in the relative humidity of the watervapor `source' area. We hypothesize that the `source' region for therain was in the boundary layer near the storm center and that becausethe hurricane was at peak intensity prior to the second day the relative humidity was higher.[PUBLICATION ABSTRACT]