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Ocean Regions (ocean + regions)

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Earth and Environmental Science	100%

Selected Abstracts

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

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 4 2010
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]

The influence of the tropical and subtropical Atlantic and Pacific Oceans on precipitation variability over Southern Central South America on seasonal time scales

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 4 2004
Guillermo J. Berri
Abstract This paper studies the temporal and spatial patterns of precipitation anomalies over southern central South America (SCSA; 22,40°S and 54,70°W), and their relationship with the sea-surface temperature (SST) variability over the surrounding tropical and subtropical Atlantic and Pacific Oceans. The data include monthly precipitation from 68 weather stations in central,northern Argentina and neighbouring Brazil, Paraguay and Uruguay, and monthly SSTs from the NOAA dataset with a 2° resolution for the period 1961,93. We use the method of canonical correlation analysis (CCA) to study the simultaneous relationship between bi-monthly precipitation and SST variability. Before applying the CCA procedure, standardized anomalies are calculated and a prefiltering is applied by means of an empirical orthogonal function (EOF) analysis. Thus, the CCA input consists of 10 EOF modes of SST and between 9 and 11 modes for precipitation and their corresponding principal components, which are the minimum number of modes necessary to explain at least 80% of the variance of the corresponding field. The results show that November,December presents the most robust association between the SST and SCSA precipitation variability, especially in northeastern Argentina and southern Brazil, followed by March,April and May,June. The period January,February, in contrast, displays a weak relationship with the oceans and represents a temporal minimum of oceanic influence during the summer semester. Based on the CCA maps, we identify the different oceanic and SCSA regions, the regional averages of SST and precipitation are calculated, and linear correlation analysis are conducted. The periods with greater association between the oceans and SCSA precipitation are November,December and May,June. During November,December, every selected region over SCSA reflects the influence of several oceanic regions, whereas during May,June only a few regions show a direct association with the oceans. The Pacific Ocean regions have a greater influence and are more widespread over SCSA; the Atlantic Ocean regions have an influence only over the northwestern and the southeastern parts of SCSA. In general, the relationship with the equatorial and tropical Atlantic and Pacific Oceans is of the type warm,wet/cold,dry, whereas the subtropical regions of both oceans show the opposite relationship, i.e. warm,dry/cold,wet. Copyright © 2004 Royal Meteorological Society [source]

The influence of the winter Arctic oscillation on the northern Russia spring temperature

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 7 2002
Vladimir N. Kryjov
Abstract Correlation and trend analyses are applied to examine relationships between the northern Russia snow/ice season surface air temperature (SAT) and winter circulation, represented by the January,March Arctic oscillation (AO) index. The 1935,99 series of winter and spring monthly SAT from five stations are used, with the winter season being defined as January,March and the spring season being defined specifically for each station in accordance with local snow/ice season duration from April,May through April,July. It is shown that the influence of the winter circulation on SAT is evident at least until the end of snow/ice season, which suggests that this influence is implemented via feedbacks provided by snow and sea ice. The winter AO accounts for some 25,50% (15,20%) of the winter (spring) SAT variance. More than 50% of the 30 year (1968,97) trends in both winter and spring SAT for northwestern Russia and more than 40% for northwestern Siberia are linearly correlated with the winter AO. It is proposed that in the Arctic Ocean regions, where snow and ice do not melt completely, the winter AO influence on SAT is likely to be evident at least until the next year's winter. Copyright © 2002 Royal Meteorological Society [source]

Individual and combined influence of El Niño,Southern Oscillation and Indian Ocean Dipole on the Tropospheric Biennial Oscillation

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 647 2010
Prasanth A. Pillai
Abstract Tropospheric biennial oscillation (TBO) is the tendency of a strong monsoon to be followed by a weaker one and vice versa. It involves both oceanic and atmospheric processes in the tropical Indian and Pacific Ocean regions. The present study analyses the effect of dynamical processes of the Indian and Pacific Oceans like the Indian Ocean Dipole (IOD) and El Niño,Southern Oscillation (ENSO) on the TBO. The 200 hPa velocity potential, 850 hPa zonal wind and sea-surface temperature datasets obtained from NCEP/NCAR reanalysis for the period 1950,2006 are used for the study of the TBO. The IOD and TBO have both in-phase (positive/negative IOD with positive/negative TBO) and out-of-phase (positive/negative IOD with negative/positive TBO) relationships. On the other hand, La Niña is associated with the positive phase of TBO and El Niño with the negative phase. In the presence of El Niño (La Niña), positive (negative) IOD is associated with negative (positive) TBO and in the absence of ENSO, positive (negative) IOD is associated with positive (negative) phase of TBO. When ENSO is associated with TBO, it tends to dominate the biennial transition irrespective of IOD. In-phase Indian to Australian monsoon transition of TBO is controlled by ENSO. IOD,TBO association is strong and significant in the absence of ENSO only. The biennial reversal is confined to the Indian Ocean in the TBO cycle associated with IOD only. Thus IOD can be considered as the local forcing for the biennial monsoon cycle, and ENSO the remote effect. Copyright © 2010 Royal Meteorological Society [source]

Statistical prediction of global sea-surface temperature anomalies

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 14 2003
A. W. Colman
Abstract Sea-surface temperature (SST) is one of the principal factors that influence seasonal climate variability, and most seasonal prediction schemes make use of information regarding SST anomalies. In particular, dynamical atmospheric prediction models require global gridded SST data prescribed through the target season. The simplest way of providing those data is to persist the SST anomalies observed at the start of the forecast at each grid point, with some damping, and this strategy has proved to be quite effective in practice. In this paper we present a statistical scheme that aims to improve that basic strategy by combining three individual methods together: simple persistence, canonical correlation analysis (CCA), and nearest-neighbour regression. Several weighting schemes were tested: the best of these is one that uses equal weight in all areas except the east tropical Pacific, where CCA is preferred. The overall performance of the combined scheme is better than the individual schemes. The results show improvements in tropical ocean regions for lead times beyond 1 or 2 months, but the skill of simple persistence is difficult to beat in the extratropics at all lead times. Aspects such as averaging periods and grid size were also investigated: results showed little sensitivity to these factors. The combined statistical SST prediction scheme can also be used to improve statistical regional rainfall forecasts that use SST anomaly patterns as predictors. Copyright © Crown Copyright 2003. Published by John Wiley & Sons, Ltd. [source]

Ocean-atmosphere-land feedbacks in an idealized monsoon

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 576 2001
C. Chou
Abstract An intermediate-complexity atmospheric model coupled with a simple land-surface model and a mixed-layer ocean model is used to investigate the processes involved in an idealized monsoon occurring on a single rectangular continent. Idealized divergences of ocean heat transports are specified as an annual average ,Q-flux'. In this simple coupled configuration, the mechanisms that affect land-ocean contrast and, in turn, the seasonal movement of the continental convergence zones are examined. These include soil-moisture feedbacks: cooling of tropical oceans by ocean transpoit; ventilation, defined as the import into continental regions of low moist static-energy air from ocean regions where heat storage opposes summer warming; and the ,interactive Rodwell-Hoskins mechanism', in which Rossby-wave-induced subsidence to the west of monsoon heating interacts with the convection zone. The fixed ocean transports have a substantial impact on the continental convection. If Q-flux is set to zero, subtropical subsidence and ventilation tend to substantially limit the poleward movement of summer monsoon rainfall. When land hydrology feedbacks are active, the drying of subtropical continents disfavours continental convection even in the tropics. When ocean transports are included, tropical oceans are slightly disfavoured as regions for producing convection which, by contrast, favours continental convection. The monsoon circulation then produces moisture transport from the ocean regions that allows substantial progression of convection into the subtropics over the eastern portion of the continent. The western portion of the continent tends to have a dry region of characteristic shape. This east-west asymmetry is partly due to the interactive Rodwell-Hoskins mechanism. The ventilation is of at least equal importance in producing east-west asymmetry and is the single most important process in limiting the poleward extent of the continental convection zone. [source]