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Maritime Continent (maritime + continent)
Selected AbstractsEvolution of tropical and extratropical precipitation anomalies during the 1997,1999 ENSO cycleINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 8 2001Scott Curtis Abstract The 1997,1999 El Niño,Southern Oscillation (ENSO) period was very powerful, but also well observed. Multiple satellite rainfall estimates combined with gauge observations allow for a quantitative analysis of precipitation anomalies in the tropics and elsewhere accompanying the 1997,1999 ENSO cycle. An examination of the evolution of the El Niño and accompanying precipitation anomalies revealed that a dry Maritime Continent (MC) preceded the formation of positive sea-surface temperature (SST) anomalies in the eastern Pacific Ocean. Thirty- to sixty-day oscillations in the winter of 1996,1997 may have contributed to this lag relationship. Furthermore, westerly wind burst events may have maintained the drought over the MC. The warming of the equatorial Pacific was then followed by an increase in convection. A rapid transition from El Niño to La Niña occurred in May 1998, but as early as October,November 1997, precipitation indices captured substantial changes in Pacific rainfall anomalies. The global precipitation patterns for this event were in good agreement with the strong consistent ENSO-related precipitation signals identified in earlier studies. Differences included a shift in precipitation anomalies over Africa during the 1997,1998 El Niño and unusually wet conditions over northeast Australia during the later stages of the El Niño. Also, the typically wet region in the north tropical Pacific was mostly dry during the 1998,1999 La Niña. Reanalysis precipitation was compared with observations during this time period and substantial differences were noted. In particular, the model had a bias towards positive precipitation anomalies and the magnitudes of the anomalies in the equatorial Pacific were small compared with the observations. Also, the evolution of the precipitation field, including the drying of the MC and eastward progression of rainfall in the equatorial Pacific, was less pronounced for the model compared with the observations. Copyright © 2001 Royal Meteorological Society [source] Simulation of the Madden, Julian Oscillation and its teleconnections in the ECMWF forecast systemTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 649 2010Frédéric Vitart Abstract A series of 46-day ensemble integrations starting on the 15th of each month from 1989 to 2008 has been completed with the European Centre for Medium-Range Weather Forecasts (ECMWF) forecast system. The Madden, Julian Oscillation (MJO) simulated by the hindcasts is diagnosed using an index based on combined empirical orthogonal functions (EOFs) of zonal winds at 200 and 850 hPa and outgoing long-wave radiation. Results indicate that the dynamical model is able to maintain the amplitude of the MJO during the 46 days of integrations and the model displays skill for up to about 20 days to predict the evolution of the MJO. However, the MJO simulated by the model has a too slow eastward propagation and has difficulties crossing the Maritime Continent. The MJO teleconnections simulated by the ECMWF forecast system have been compared to reanalyses. In the Tropics, the impact of the MJO on precipitation is generally consistent with reanalysis. In the Northern Extratropics, the MJO simulated by the model has an impact on North Atlantic weather regimes, but with a smaller amplitude than in reanalysis which can be partly explained by the too slow eastward propagation of the simulated MJO events. The impact of the MJO on the probabilistic skill scores has been assessed. Results indicate that the MJO simulated by the model has a statistically significant impact on weekly mean probabilistic skill scores in the Northern Extratropics, particularly at the time range 19, 25 days. At this time range, the reliability of the probabilistic forecasts over Europe depends strongly on the presence of an MJO event in the initial conditions. This result confirms that the MJO is a major source of predictability in the Extratropics in the sub-seasonal time-scale. Copyright © 2010 Royal Meteorological Society [source] A multi-time scale Australian monsoon indexINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 8 2010Yoshiyuki Kajikawa Abstract A broad-scale Australian monsoon index (AUSMI) describing multi-time scale variations is defined by using 850 hPa zonal wind averaged over the area (5°S,15°S, 110°E,130°E). This circulation index reflects monsoonal rainfall variability over Northern Australia and maritime continent. The index can be used to depict the seasonal cycle (for instance the onset) and measure the intraseasonal, interannual, and interdecadal variations of the Australian monsoon. The interannual variation of the Australian monsoon onset determined by the AUSMI agrees well with that derived from the rainfall and winds at Darwin in the previous studies. We found a significant anti-correlation between the monsoon onset date and the seasonal (DJF) mean AUSMI anomalies; namely an early onset is accompanied by a strong Australian summer monsoon and vice versa. These interannual variations are also strongly associated with El Niño-Southern Oscillation (ENSO). In contrast, the retreat dates are not significantly different between the strong and weak Australian summer monsoon years. The AUSMI is useful in monitoring the weather and climate variations of the Australian monsoon and validating the performance of climate models. Copyright © 2009 Royal Meteorological Society [source] Variability of the recent climate of eastern AfricaINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 6 2004Carl J. Schreck III Abstract The primary objective of this study is to investigate the recent variability of the eastern African climate. The region of interest is also known as the Greater Horn of Africa (GHA), and comprises the countries of Burundi, Djibouti, Eritrea, Ethiopia, Kenya, Rwanda, Somalia, Sudan, Uganda, and Tanzania. The analysis was based primarily on the construction of empirical orthogonal functions (EOFs) of gauge rainfall data and on CPC Merged Analysis of Precipitation (CMAP) data, derived from a combination of rain-gauge observations and satellite estimates. The investigation is based on the period 1961,2001 for the ,short rains' season of eastern Africa of October through to December. The EOF analysis was supplemented by projection of National Centers for Environmental Prediction wind data onto the rainfall eigenmodes to understand the rainfall,circulation relationships. Furthermore, correlation and composite analyses have been performed with the Climatic Research Unit globally averaged surface-temperature time series to explore the potential relationship between the climate of eastern Africa and global warming. The most dominant mode of variability (EOF1) based on CMAP data over eastern Africa corresponds to El Niño,southern oscillation (ENSO) climate variability. It is associated with above-normal rainfall amounts during the short rains throughout the entire region, except for Sudan. The corresponding anomalous low-level circulation is dominated by easterly inflow from the Indian Ocean, and to a lesser extent the Congo tropical rain forest, into the positive rainfall anomaly region that extends across most of eastern Africa. The easterly inflow into eastern Africa is part of diffluent outflow from the maritime continent during the warm ENSO events. The second eastern African EOF (trend mode) is associated with decadal variability. In distinct contrast from the ENSO mode pattern, the trend mode is characterized by positive rainfall anomalies over the northern sector of eastern Africa and opposite conditions over the southern sector. This rainfall trend mode eluded detection in previous studies that did not include recent decades of data, because the signal was still relatively weak. The wind projection onto this mode indicates that the primary flow that feeds the positive anomaly region over the northern part of eastern Africa emanates primarily from the rainfall-deficient southern region of eastern Africa and Sudan. Although we do not assign attribution of the trend mode to global warming (in part because of the relatively short period of analysis), the evidence, based on our results and previous studies, strongly suggests a potential connection. Copyright © 2004 Royal Meteorological Society. [source] Response of the Asian summer monsoon to changes in El Niño propertiesTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 607 2005H. Annamalai Abstract Diagnostics from observed precipitation and National Centers for Environmental Prediction,National Center for Atmospheric Research re-analysis products reveal that after the 1976,77 climate shift in the Pacific there was a dramatic change in the response of the Indian summer monsoon (ISM) to El Niño, particularly during the months of July and August. Based on 1950,75 (PRE76) and 1977,2001 (POST76) El Niño composites: the western North Pacific monsoon (WNPM) was stronger than normal in both periods; the ISM was weaker than normal during the entire monsoon season in PRE76, but in POST76 was weaker only during the onset and withdrawal phases. In terms of observed sea surface temperature (SST) during July,August, the major differences between the two periods are the presence of cold SST anomalies over the Indo,Pacific warm pool and the intensity of warm SST anomalies in the central Pacific in POST76. The effect of these differences on the ISM is investigated in a suite of experiments with an Atmospheric General Circulation Model (AGCM) that has a realistic monsoon precipitation climatology. Separate ten-member ensemble simulations with the AGCM were conducted for PRE76 and POST76 El Niño events with SST anomalies inserted as follows: (i) tropical Indo,Pacific (TIP), (ii) tropical Pacific only (TPO), and (iii) tropical Indian Ocean only (TIO). Qualitatively, TPO solutions reproduce the observed differences in the monsoon response in both periods. Specifically, during July,August of POST76 the cold SST anomalies in conjunction with remote subsidence suppress precipitation (3,5 mm day,1) over the maritime continent and equatorial central Indian Ocean. Inclusion of Indian Ocean SST anomalies in the TIP runs further suppresses precipitation over the entire equatorial Indian Ocean. The low-level anticyclonic circulation anomalies that develop as a Rossby-wave response to these convective anomalies increase the south-westerlies over the northern Indian Ocean, and favour a stronger ISM and WNPM. During PRE76 the non-occurrence of cold SST anomalies over the Indo,Pacific warm pool reinforces El Niño's suppression on the ISM. In contrast, TIO solutions show a reduced ISM during July,August of POST76; the solutions, however, show a significant effect on the WNPM during both PRE76 and POST76 periods. It is argued that SSTs over the entire tropical Indo,Pacific region need to be considered to understand the El Niño Southern Oscillation,monsoon linkage, and to make predictions of rainfall over India and the western North Pacific. Copyright © 2005 Royal Meteorological Society [source] Long-term trends of winter monsoon synoptic circulations over the maritime continent: 1962,2007,ATMOSPHERIC SCIENCE LETTERS, Issue 3 2010Liew Juneng Abstract The present study examines the long-term trends of the winter monsoon northeasterly cold surge and Borneo vortex over the South China Sea. There has been a significant increase in the frequency of the Borneo vortex within the study period of 1962,2007. The location of the center of the Borneo vortices has shifted slightly offshore; northward of western Borneo. This could result in less vortex,land interaction and lengthen the life span of the vortices due to less frictional shear and hence increase the vortex days. These changes could be related to the strengthened easterly component of the cold surge winds. Copyright © 2010 Royal Meteorological Society [source] | ||||||||||