Observed annual and interannual variations in tropospheric water vapor
Radiosonde observations from a global network of 56 radiosonde stations for 1973-1990 are used to describe and quantify annual and interannual variations of tropospheric water vapor. Taking care to identify data inhomogeneities related to changes in instruments or observing practices, monthly mean and anomaly data sets are constructed for dew point, specific humidity, relative humidity, temperature and precipitable water from the surface to 500 mb. Local annual cycles of tropospheric humidity can be classified according to the amplitude and phase of humidity variations which define five humidity regimes. For two regimes, both in middle and high latitudes, relative humidity is fairly constant while the annual cycle of precipitable water is in phase with that of temperature. At some midlatitude stations with a monsoon-like climate, seasonal relative humidity variations are large. In the tropics, seasonal relative humidity variations, especially above the boundary layer, dominate the annual cycle of precipitable water, and precipitable water variations are not related to temperature variations. Correlations of temperature and specific humidity anomalies are generally positive outside the tropics, suggesting that atmospheric warming is associated with increases in water vapor content. However, correlations of temperature and relative humidity anomalies are sometimes not significant and are often negative (e.g., in mid- and high latitude continental regions). Thus relative humidity is not always insensitive to temperature changes. In the tropics, tropospheric water vapor and temperature variations are not well correlated. An empirical orthogonal function analysis of tropical specific humidity variations identified two important modes of variability. The first is a step-like increase in specific humidity that occurred in about 1976-1977, and the second is associated with the El Nino phenomenon.
- Research Organization:
- Maryland Univ., College Park, MD (United States)
- OSTI ID:
- 6316477
- Country of Publication:
- United States
- Language:
- English
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