Changes In Monsoon Rainfall Research Articles

On interannual characteristics of Climate Prediction Center merged analysis precipitation over the Korean peninsula during the summer monsoon season

AbstractTo improve understanding of the characteristics of large‐scale environments associated with summer monsoon precipitation in Korea, we have constructed an index to measure the Changma using area‐averaged and period‐averaged Climate Prediction Center merged analysis precipitation over Korea during the years 1979–2001. Strong and weak Changma years are defined as years in which the precipitation anomaly is over ±0.5σ. The domain and period for this analysis are selected over the Korean peninsula (31.25–41.25 °N, 123.75–131.25 °E) from late June to late July. In strong Changma years, strong upper level divergence occurs near the Korean peninsula, located at the entrance of the mid‐latitude jet core, leading to low pressure in the lower layer. Between strong and weak Changma years, 850 hPa southwesterly flows are significant throughout the East China Sea and southern Japan.Clear differences exist between strong and weak Changma years. Weak Changma is well correlated with a weak Pacific high, as seen in the changes in sea‐level pressure and 500 hPa geopotential height, and wind speed in the lower level jet. Strong Changma is well correlated with strong migratory highs in northern parts of the Korean peninsula. It is shown that the long‐term changes in summer monsoon rainfall, such as those between the two climate regimes of 1979–92 and 1993–2001, are characterized by a shift of maximum rainfall periods from late July to mid August. Copyright © 2005 Royal Meteorological Society

Climate Changes in the 21st Century over the Asia-Pacific Region Simulated by the NCAR CSM and PCM

The Climate System Model (CSM) and the Parallel Climate Model (PCM), two coupled global climate models without flux adjustments recently developed at NCAR, were used to simulate the 20th century climate using historical greenhouse gas and sulfate aerosol forcing. These simulations were extended through the 21st century under two newly developed scenarios, a business-as-usual case (BAU, CO2 ≈ 710 ppmv in 2100) and a CO2 stabilization case (STA550, CO2 ≈ 540 ppmv in 2100). The simulated changes in temperature, precipitation, and soil moisture over the Asia-Pacific region (10°–60°N, 55°–155°E) are analyzed, with a focus on the East Asian summer monsoon rainfall and climate changes over the upper reaches of the Yangtze River. Under the BAU scenario, both the models produce surface warming of about 3–5°C in winter and 2–3°C in summer over most Asia. Under the STA550 scenario, the warming is reduced by 0.5–I.0°C in winter and by 0.5°C in summer. The warming is fairly uniform at the low latitudes and does not induce significant changes in the zonal mean Hadley circulation over the Asia-Pacific domain. While the regional precipitation changes from single CSM integrations are noisy, the PCM ensemble mean precipitation shows 10%–30% increases north of ~ 30°N and ~ 10% decreases south of ~ 30°N over the Asia-Pacific region in winter and 10%–20% increases in summer precipitation over most of the region. Soil moisture changes are small over most Asia. The CSM single simulation suggests a 30% increase in river runoff into the Three Gorges Dam, but the PCM ensemble simulations show small changes in the runoff.

All-India Summer Monsoon Rainfall and Sea Surface Temperatures around Northern Australia and Indonesia

Abstract The relationship between Indian summer (June–September) monsoon rainfall and sea surface temperatures around northern Australia–Indonesia has been explored using data from 1949 to 1991. Warm sea surface temperatures are generally associated with a good monsoon; a poor monsoon is usually accompanied and preceded by low sea surface temperatures. This finding confirms, on independent data, a suggestion made a decade ago. This study also confirms a relationship between changes in Darwin pressure and Indian monsoon rainfall. Thew two relationships appear to provide a method for predicting Indian summer monsoon rainfall a month or two before the onset of the monsoon season. Two predictors (April sea surface temperatures and the change in Darwin pressure from January to April) together account for about 50% of the variance in Indian monsoon rainfall if the data are adjusted to remove possible artificial trends in the ocean temperatures. The northern Australia–Indonesia region is clearly an important com...

Macro‐regional definition and characteristics of Indian summer monsoon rainfall, 1871–1985

AbstractA case is made for regional‐scale Indian summer monsoon rainfall data and analysis, intermediate between the widely used all‐India and meteorological subdivision data sets. Macro‐regional units are constructed from the data provided by Parthasarathy et al., 10 being defined using principal components analysis and a classification algorithm. The temporal changes of summer monsoon rainfall over the period 1871–1985 are analysed and described for each of these regions, and the marked diversity of fluctuations between the regions is emphasized by a variety of methods. The degree of relationship is considered for each region between drier and wetter conditions and (i) El Niño and non‐El Niño years, and (ii) SST anomalies in the eastern tropical Pacific. Clear regional differences are apparent, but even statistically highly significant relationships are not large in any absolute sense. The need for explanatory analyses at the regional scale, in addition to those at the more common all‐India scale, is stressed.