Monsoon System (monsoon + system)

Distribution by Scientific Domains

Selected Abstracts

Pilot study of latewood-width of conifers as an indicator of variability of summer rainfall in the North American monsoon region

David M. Meko
Abstract The variability of the North American Monsoon System (NAMS) is important to the precipitation climatology of Mexico and the southwestern United States. Tree-ring studies have been widely applied to climatic reconstruction in western North America, but as yet, have not addressed the NAMS. One reason is the need for highly resolved seasonal dendroclimatic information. Latewood-width, the portion of the annual tree ring laid down late in the growing season, can potentially yield such information. This paper describes a pilot study of the regional summer precipitation signal in latewood-width from a network of five Pseudotsuga menziesii chronologies developed in the heart of the region of NAMS influence in Arizona, USA. Exploratory data analysis reveals that the summer precipitation signal in latewood is strong, but not equally so over the full range of summer precipitation. Scatter in the relationship increases toward higher levels of precipitation. Adjustment for removal of inter-correlation with earlywood-width appears to strengthen the summer precipitation signal in latewood-width. To demonstrate a possible application to climatic reconstruction, the latewood precipitation signal is modelled using a nonlinear model,a binary recursive classification tree (CT) that attempts to classify summers as dry or not dry from threshold values of latewood-width. The model identifies narrow latewood-width as an effective predictor of a dry summer. Of 14 summers classified dry by latewood-width for the period 1868,1992, 13 are actually dry by the instrumental precipitation record. The results suggest that geographical expansion of coverage by latewood-width chronologies and further development of statistical methods may lead to successful reconstruction of variability of the NAMS on century time scales. Copyright © 2001 Royal Meteorological Society [source]

Evaluation of high-resolution precipitation estimate over the Amazon Basin

Cláudio Moisés Santos e Silva
Abstract Using rainfall data from S-band radar measurements, the estimative of the rainfall from the 3B42_V6 algorithm was evaluated for the region of the Tropical Rainfall Measurement Mission and Large Scale Biosphere,Atmosphere Experiment in Amazonia (TRMM,LBA) experiment, which was conducted in the Amazon Basin during the 1999 rainy season. The algorithm correctly represented the diurnal rainfall cycle, but underestimated overall precipitation rates by about 50%. It adequately represented most of the stratiform (convective) rainfall during the break (active) phase of the South American Monsoon System (SAMS). Thus, some uncertainties, as well as the algorithm applicability for the region and period studied, were demonstrated. Copyright © 2009 Royal Meteorological Society [source]

Monsoon in the Americas: Opportunities and Challenges

Thomas M. Rickenbach
This article presents a comparative review of the North and South America Monsoon Systems and highlights the challenges and opportunities presented to those regions by the seasonal rains. Monsoon precipitation represents a major component of the water resources available to the southwestern US and to Brazil. Although each system shares classical features of the well-known southwest Indian monsoon, water use, agriculture, public safety, and energy policy in these two countries have been shaped by the unique regional complexities of monsoon rain across each region. A comparison between these two systems may offer perspective for ways by which these societies may adapt to current and future challenges, and take advantage of new opportunities. [source]

Effect of late 1970's climate shift on tropospheric biennial oscillation,role of local Indian Ocean processes on Asian summer monsoon

Prasanth A Pillai
Abstract The tropical climate has undergone noticeable changes on interdecadal time scales. The climate shift that occurred in the late 1970s attained enormous attention owing to its global-scale variations in ocean temperature, heat content and El Nino Southern Oscillation (ENSO) properties. Earlier studies presented the effect of this shift on ENSO and the Asian summer monsoon,ENSO relationship. The present study is an attempt to investigate the effect of late 1970's climate shift on tropospheric biennial oscillation (TBO), which is an important tropical phenomenon that includes both air,sea processes in the tropical Indian and Pacific Ocean regions. TBO is the tendency for the Asian,Australian monsoon system to alternate between relatively strong and weak years. The study comprises a detailed analysis of the TBO cycle in the time periods before (1951,1975) and after (1978,2002) the climate shift in 1976 with the help of National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) data sets of 200-hPa velocity potential; the Indian Ocean sea surface temperature (SST) and circulation are more obvious after the shift, although they were significant in the Pacific Ocean before 1976. The effect of ENSO in the biennial cycle is reduced with climate shift. The persistence of Asian-to-Australian summer monsoon has weakened in recent decades, as it is controlled by ENSO. Local oceanic processes in the Indian Ocean and local monsoon Hadley circulation have an increased role in the biennial oscillation of the Asian summer monsoon after 1976. Copyright © 2009 Royal Meteorological Society [source]

Inter-decadal variation of the summer precipitation in East China and its association with decreasing Asian summer monsoon.

Part I: Observed evidences
Abstract In recent two decades, North and Northeast China have suffered from severe and persistent droughts while the Yangtze River basin and South China have undergone much more significant heavy rainfall/floods events. This long-term change in the summer precipitation and associated large-scale monsoon circulation features have been examined by using the new dataset of 740 surface stations for recent 54 years (1951,2004) and about 123-yr (1880,2002) records of precipitation in East China. The following new findings have been highlighted: (1) One dominating mode of the inter-decadal variability of the summer precipitation in China is the near-80-yr oscillation. Other modes of 12-yr and 30,40-yr oscillations also play an important role in affecting regional inter-decadal variability. (2) In recent 54 years, the spatial pattern of the inter-decadal variability of summer precipitation in China is mainly structured with two meridional modes: the dipole pattern and the positive-negative-positive ("+ , + " pattern). In this period, a regime transition of meridional precipitation mode from "+ , + " pattern to dipole pattern has been completed. In the process of southward movement of much precipitation zone, two abrupt climate changing points that occurred in 1978 and 1992, respectively, were identified. (3) Accompanying the afore-described precipitation changes, the East Asian summer monsoon have experienced significant weakening, with northward moisture transport and convergence by the East Asian summer monsoon greatly weakened, thus leading to much deficient moisture supply for precipitation in North China. (4) The significant weakening of the component of the tropical upper-level easterly jet (TEJ) has made a dominating contribution to the weakening of the Asian summer monsoon system. The cooling in the high troposphere at mid- and high latitudes and the possible warming at low latitude in the Asian region is likely to be responsible for the inter-decadal weakening of the TEJ. Copyright © 2007 Royal Meteorological Society [source]

Observed ENSO teleconnections with the South American monsoon system

V. Krishnamurthy
Abstract This study establishes from observations that there exists a spatially coherent and seasonally persistent association of El Niño and Southern Oscillation(ENSO) with the South American monsoon variability over a large region that includes central-east part of South America. This result is confirmed using both remote sensing data of outgoing long-wave radiation and in situ rain gauge observations independently. This slowly varying atmospheric pattern has very high daily correlation with the sea surface temperature(SST) over the tropical Pacific and Indian Oceans. The December-to-March seasonal mean of the rainfall is often determined by this ENSO-related pattern. Copyright © 2010 Royal Meteorological Society [source]

What causes the extremely heavy rainfall in Taiwan during Typhoon Morakot (2009)?

Dr Xuyang Ge
Abstract Despite its category-2 intensity only, Typhoon (tropical cyclone in the Western Pacific) Morakot produced a record-breaking rainfall in Taiwan. A cloud-resolving model is used to simulate this extreme rainfall event and understand the dynamic aspect under this event. Due to the interaction between Morakot and a monsoon system, a peripheral gale force monsoon surge appears to the south of Taiwan. The monsoon surge remains even in a sensitivity experiment in which Taiwan terrain is reduced. However, the rainfall amount in Taiwan is greatly reduced without high topography over Taiwan, suggesting the important role the local topography plays in producing heavy rainfall. The overall numerical results indicate that it is the interaction among the typhoon, monsoon system, and local terrain that led to this extreme event. Copyright © 2010 Royal Meteorological Society [source]

Simulation of the Asian summer monsoon in five European general circulation models

G. M. Martin
Abstract A comparison is made of the mean monsoon climatology in five different general circulation models (GCMs) which have been used by the participants of a project, funded by the European Union, entitled Studies of the Influence, Hydrology and Variability of the Asian summer monsoon (SHIVA). The models differ considerably, in horizontal and vertical resolution, numerical schemes and physical parametrizations, so that it is impossible to isolate the cause of differences in their monsoon simulations. Instead, the purpose of this comparison is to document and compare the representation of the mean monsoon in models which are being used to investigate the characteristics of the monsoon, its variability and its response to different boundary forcings. All of the models produce a reasonable representation of the monsoon circulation, although there are regional variations in the magnitude and pattern of the flow at both 850 hPa and 200 hPa. Considerable differences between the models are seen in the amount and distribution of precipitation. The models all reproduce the basic monsoon seasonal variation, although the timing of the onset and retreat, and the maxima in the winds and precipitation during the established phase, differ between them. There are corresponding differences in the evolution of the atmospheric structure between the pre-monsoon season and its established phase. It is hoped that this study will set in context the investigations of the monsoon system and its impacts carried out using these models, both during SHIVA and in the future. Copyright © 2000 Royal Meteorological Society. [source]

A regional climate study of Central America using the MM5 modeling system: results and comparison to observations

Jose L. Hernandez
Abstract The Mesoscale Modeling system, version 3.6 (MM5) regional modeling system has been applied to Central America and has been evaluated against National Oceanic and Atmospheric Administration/National Climatic Data Center (NOAA/NCDC) daily observations and the Global Precipitation Climatology Project (GPCP) precipitation data. We compare model results and observations for 1997 and evaluate various climate parameters (temperature, wind speed, precipitation and water vapor mixing ratio), emphasizing the differences within the context of the station dependent geographical features and the land use (LU) categories. At 9 of the 16 analyzed stations the modeled temperature, wind speed and vapor mixing ratio are in agreement with observations with average model-observation differences consistently lower than 25%. MM5 has better performance at stations strongly impacted by monsoon systems, regions typified by low topography in coastal areas and areas characterized by evergreen, broad-leaf and shrub land vegetation types. At four stations the model precipitation is about a factor of 3,5 higher than the observations, while the simulated wind is roughly twice what is observed. These stations include two inland stations characterized by croplands close to water bodies; one coastal station in El Salvador adjacent to a mountain-based cropland area and one station at sea-level. This suggests that the model does not adequately represent the influence of topographic features and water bodies close to these stations. In general, the model agrees reasonably well with measurements and therefore provides an acceptable description of regional climate. The simulations in this study use only two seasonal maps of land cover. The main model discrepancies are likely attributable to the actual annual cycle of land,atmosphere vapor and energy exchange that has a temporal scale of days to weeks. These fluxes are impacted by surface moisture availability, albedo and thermal inertia parameters. Copyright © 2006 Royal Meteorological Society. [source]