Abstract:
The atmospheric branch of the hydrological cycle (AWC) is of considerable interest as it responds to changes in the energy cycle, greenhouse gases, aerosols and many other factors in the climate system. This PhD thesis investigates the components of the AWC from current radiosonde, reanalysis and blended datasets for the Southwest Pacific region. Examination of measurements of tropospheric humidity reveals outstanding issues in the radiosonde data, which requires some remedy measures be taken. After implementing a homogenization procedure to correct for biases and artificial changepoints in the data series, it is found that specific humidity exhibits spatially more consistent moistening at the 850 hPa level over most of the Southwest Pacific region and a contrast at 500 hPa between the moistening in the tropics and a drying in the subtropical South Pacific. An assessment is made of the balance of the estimated atmospheric water budgets. It is found that the budgets are far from closed even on the climatological time scale mainly due to issues in the estimates of precipitation (P) and evaporation (E). Therefore, it is advised to avoid the use of E – P in hydroclimate studies where the absolute amplitude is important. Variability of atmospheric moisture transport on different time scales has been explored. While the seasonally varying monthly mean of specific humidity ( ) and wind ( ) is the largest component to the total moisture transport in the tropics, the short term variations of and dominate the total moisture transport in the extratropics. Interannual extremes in moisture transport over New Zealand and their relationship to large-scale circulation are investigated. Changes in the dynamical component of moisture transport related to wind anomalies are the primary contributor to the extremes. Further analysis shows that these changes are driven by hemispheric scale longitudinal waves in the mid latitudes. The connection between moisture transport and precipitation variability is tight such that many of the anomalous precipitation events are associated with extreme moisture convergence/divergence. However, there are some instances where precipitation anomalies are explained by a combination of marginal deviation in evaporation and moisture transport. Evaporation alone is not a decisive factor for precipitation anomalies.