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- Author or Editor: Qing Wang x
- Journal of Hydrometeorology x
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Abstract
Floods and droughts hit southwest China (SWC) frequently, especially over the last decade. In this study, the dominant modes of summer rainfall anomalies over SWC on the interannual time scale and the possible causes are investigated. Interannual variability of the summer rainfall over SWC has two dominant modes. The first mode features rainfall increases over most of SWC except central Sichuan, and the second mode exhibits wet conditions in the north but dry conditions in the south. The suppressed convection over the Philippine Sea affects the first mode by inducing anomalous anticyclones over the western North Pacific and to the south of the Tibetan Plateau, which transport more water vapor to eastern Tibet and eastern SWC and hence favor above-normal rainfall there. The enhanced convection over the western Maritime Continent could generate similar atmospheric circulation anomalies associated with the suppressed convection over the Philippine Sea but with a northward shift, resulting in significant increases in rainfall over northeastern SWC but weak decreases in rainfall over southeastern SWC. As a result, the rainfall anomalies over SWC tend to be different between El Niño–Southern Oscillation decaying and developing phases because their different impacts on the convection over the Philippine Sea and the western Maritime Continent. Meanwhile, the sea surface temperature in the tropical southeastern Indian Ocean also plays an important role in variability of the rainfall over SWC because of its significant impact on the convection over the western Maritime Continent.
Abstract
Floods and droughts hit southwest China (SWC) frequently, especially over the last decade. In this study, the dominant modes of summer rainfall anomalies over SWC on the interannual time scale and the possible causes are investigated. Interannual variability of the summer rainfall over SWC has two dominant modes. The first mode features rainfall increases over most of SWC except central Sichuan, and the second mode exhibits wet conditions in the north but dry conditions in the south. The suppressed convection over the Philippine Sea affects the first mode by inducing anomalous anticyclones over the western North Pacific and to the south of the Tibetan Plateau, which transport more water vapor to eastern Tibet and eastern SWC and hence favor above-normal rainfall there. The enhanced convection over the western Maritime Continent could generate similar atmospheric circulation anomalies associated with the suppressed convection over the Philippine Sea but with a northward shift, resulting in significant increases in rainfall over northeastern SWC but weak decreases in rainfall over southeastern SWC. As a result, the rainfall anomalies over SWC tend to be different between El Niño–Southern Oscillation decaying and developing phases because their different impacts on the convection over the Philippine Sea and the western Maritime Continent. Meanwhile, the sea surface temperature in the tropical southeastern Indian Ocean also plays an important role in variability of the rainfall over SWC because of its significant impact on the convection over the western Maritime Continent.
Abstract
Complex terrain poses challenges to the ground-based radar quantitative precipitation estimation (QPE) because of partial or total blockages of radar beams in the lower tilts. Reflectivities from higher tilts are often used in the QPE under these circumstances and biases are then introduced due to vertical variations of reflectivity. The spaceborne Precipitation Radar (PR) on board the Tropical Rainfall Measuring Mission (TRMM) satellite can provide good measurements of the vertical structure of reflectivity even in complex terrain, but the poor temporal resolution of TRMM PR data limits their usefulness in real-time QPE. This study proposes a novel vertical profile of reflectivity (VPR) correction approach to enhance ground radar–based QPEs in complex terrain by integrating the spaceborne radar observations. In the current study, climatological relationships between VPRs from an S-band Doppler weather radar located on the east coast of Taiwan and the TRMM PR are developed using an artificial neural network (ANN). When a lower tilt of the ground radar is blocked, higher-tilt reflectivity data are corrected with the trained ANN and then applied in the rainfall estimation. The proposed algorithm was evaluated with three typhoon precipitation events, and its preliminary performance was evaluated and analyzed.
Abstract
Complex terrain poses challenges to the ground-based radar quantitative precipitation estimation (QPE) because of partial or total blockages of radar beams in the lower tilts. Reflectivities from higher tilts are often used in the QPE under these circumstances and biases are then introduced due to vertical variations of reflectivity. The spaceborne Precipitation Radar (PR) on board the Tropical Rainfall Measuring Mission (TRMM) satellite can provide good measurements of the vertical structure of reflectivity even in complex terrain, but the poor temporal resolution of TRMM PR data limits their usefulness in real-time QPE. This study proposes a novel vertical profile of reflectivity (VPR) correction approach to enhance ground radar–based QPEs in complex terrain by integrating the spaceborne radar observations. In the current study, climatological relationships between VPRs from an S-band Doppler weather radar located on the east coast of Taiwan and the TRMM PR are developed using an artificial neural network (ANN). When a lower tilt of the ground radar is blocked, higher-tilt reflectivity data are corrected with the trained ANN and then applied in the rainfall estimation. The proposed algorithm was evaluated with three typhoon precipitation events, and its preliminary performance was evaluated and analyzed.
Abstract
This paper intends to investigate the time scales of land surface hydrology and enhance the understanding of the hydrological cycle between the atmosphere, vegetation, and soil. A three-layer model for land surface hydrology is developed to study the temporal variation and vertical structure of water reservoirs in the vegetation–soil system in response to precipitation forcing. The model is an extension of the existing one-layer bucket model. A new time scale is derived, and it better represents the response time scale of soil moisture in the root zone than the previously derived inherent time scale (i.e., the ratio of the field capacity to the potential evaporation). It is found that different water reservoirs of the vegetation–soil system have different time scales. Precipitation forcing is mainly concentrated on short time scales with small low-frequency components, but it can cause long time-scale disturbances in the soil moisture of root zone. This time scale increases with soil depth, but it can be reduced significantly under wetter conditions. Although the time scale of total water content in the vertical column in the three-layer model is similar to that of the one-layer bucket model, the time scale of evapotranspiration is very different. This suggests the need to consider the vertical structure in land surface hydrology reservoirs and in climate study.
Abstract
This paper intends to investigate the time scales of land surface hydrology and enhance the understanding of the hydrological cycle between the atmosphere, vegetation, and soil. A three-layer model for land surface hydrology is developed to study the temporal variation and vertical structure of water reservoirs in the vegetation–soil system in response to precipitation forcing. The model is an extension of the existing one-layer bucket model. A new time scale is derived, and it better represents the response time scale of soil moisture in the root zone than the previously derived inherent time scale (i.e., the ratio of the field capacity to the potential evaporation). It is found that different water reservoirs of the vegetation–soil system have different time scales. Precipitation forcing is mainly concentrated on short time scales with small low-frequency components, but it can cause long time-scale disturbances in the soil moisture of root zone. This time scale increases with soil depth, but it can be reduced significantly under wetter conditions. Although the time scale of total water content in the vertical column in the three-layer model is similar to that of the one-layer bucket model, the time scale of evapotranspiration is very different. This suggests the need to consider the vertical structure in land surface hydrology reservoirs and in climate study.
