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Carvalho L.M.V.,University of California at Santa Barbara | Carvalho L.M.V.,University of Sao Paulo | Jones C.,University of California at Santa Barbara | Silva A.E.,University of Sao Paulo | And 3 more authors.
International Journal of Climatology

The South American Monsoon System (SAMS) is characterised by intense convective activity and precipitation during austral summer. This study investigates changes in the onset, demise and duration of SAMS during 1948-2008. The results show a significant change in these characteristics in the early 1970s. Onset becomes steadily earlier from 1948 to early 1970s and has occurred earlier than 23-27 October after 1972-1973. Demise dates have remained later than 21-25 April after the mid-to-late 1970s. SAMS duration shows a statistical changepoint in the summer of 1971-1972 such that the mean duration was ∼170 days (1948-1972) and 195 days (1972-1982). Vertically integrated moisture flux is used to diagnose changes in mean state and reveal statistically significant increases over South America after 1971-1972. © 2010 Royal Meteorological Society. Source

Carvalho L.M.V.,University of California at Santa Barbara | Carvalho L.M.V.,University of Sao Paulo | Silva A.E.,University of Sao Paulo | Jones C.,University of California at Santa Barbara | And 4 more authors.
Climate Dynamics

This paper examines moisture transport on intraseasonal timescales over the continent and over the South Atlantic convergence zone (SACZ) during the South America (SA) summer monsoon. Combined Empirical Orthogonal Function analysis (EOFc) of Global Precipitation Climatology Project pentad precipitation, specific humidity, air temperature, zonal and meridional winds at 850 hPa (NCEP/NCAR reanalysis) are performed to identify the large-scale variability of the South America monsoon system and the SACZ. The first EOFc was used as a large-scale index for the South American monsoon (LISAM), whereas the second EOFc characterized the SACZ. LISAM (SACZ) index showed spectral variance on 30-90 (15-20) days and were both band filtered (10-100 days). Intraseasonal wet anomalies were defined when LISAM and SACZ anomalies were above the 75th percentile of their respective distribution. LISAM and SACZ wet events were examined independently of each other and when they occur simultaneously. LISAM wet events were observed with the amplification of wave activity in the Northern Hemisphere and the enhancement of northwesterly cross-equatorial moisture transport over tropical continental SA. Enhanced SACZ was observed with moisture transport from the extratropics of the Southern Hemisphere. Simultaneous LISAM and SACZ wet events are associated with cross-equatorial moisture transport along with moisture transport from Subtropical Southwestern Atlantic. © 2010 The Author(s). Source

Carvalho L.M.V.,University of California at Santa Barbara | Jones C.,University of California at Santa Barbara | Posadas A.N.D.,International Potato Center | Quiroz R.,International Potato Center | And 2 more authors.
Journal of Climate

The South American monsoon system (SAMS) is the most important climatic feature in South America and is characterized by pronounced seasonality in precipitation during the austral summer. This study compares several statistical properties of daily gridded precipitation from different data (1998-2008): 1) Physical Sciences Division (PSD), Earth System Research Laboratory [1.08 and 2.58 latitude (lat)/longitude (lon)]; 2) Global Precipitation Climatology Project (GPCP; 18 lat/lon); 3) Climate Prediction Center (CPC) unified gauge (CPC-uni) (0.58 lat/lon); 4) NCEP Climate Forecast System Reanalysis (CFSR) (0.58 lat/lon); 5) NASA Modern-Era Retrospective Analysis for Research and Applications (MERRA) reanalysis (0.58 lat/0.38 lon); and 6) Tropical Rainfall Measuring Mission (TRMM) 3B42 V6 data (0.258 lat/lon). The same statistical analyses are applied to data in 1) a common 2.58 lat/lon grid and 2) in the original resolutions of the datasets. All datasets consistently represent the large-scale patterns of the SAMS. The onset, demise, and duration of SAMS are consistent among PSD, GPCP, CPC-uni, and TRMMdatasets, whereas CFSR and MERRA seem to have problems in capturing the correct timing of SAMS. Spectral analyses show that intraseasonal variance is somewhat similar in the six datasets. Moreover, differences in spatial patterns of mean precipitation are small among PSD, GPCP, CPC-uni, and TRMM data, while some discrepancies are found in CFSR and MERRA relative to the other datasets. Fitting of gamma frequency distributions to daily precipitation shows differences in the parameters that characterize the shape, scale, and tails of the frequency distributions. This suggests that significant uncertainties exist in the characterization of extreme precipitation, an issue that is highly important in the context of climate variability and change in South America. © 2012 American. Meteorological Society. Source

Blade I.,University of Barcelona | Blade I.,Institute Catal Of Cincies Del Clima | Fortuny D.,University of Barcelona | Van Oldenborgh G.J.,Royal Netherlands Meteorological Institute | And 2 more authors.
Journal of Geophysical Research: Atmospheres

This paper discusses uncertainties in model projections of summer drying in the Euro-Mediterranean region related to errors and uncertainties in the simulation of the summer NAO (SNAO). The SNAO is the leading mode of summer SLP variability in the North Atlantic/European sector and modulates precipitation not only in the vicinity of the SLP dipole (northwest Europe) but also in the Mediterranean region. An analysis of CMIP3 models is conducted to determine the extent to which models reproduce the signature of the SNAO and its impact on precipitation and to assess the role of the SNAO in the projected precipitation reductions. Most models correctly simulate the spatial pattern of the SNAO and the dry anomalies in northwest Europe that accompany the positive phase. The models also capture the concurrent wet conditions in the Mediterranean, but the amplitude of this signal is too weak, especially in the east. This error is related to the poor simulation of the upper-level circulation response to a positive SNAO, namely the observed trough over the Balkans that creates potential instability and favors precipitation. The SNAO is generally projected to trend upwards in CMIP3 models, leading to a consistent signal of precipitation reduction in NW Europe, but the intensity of the trend varies greatly across models, resulting in large uncertainties in the magnitude of the projected drying. In the Mediterranean, because the simulated influence of the SNAO is too weak, no precipitation increase occurs even in the presence of a strong SNAO trend, reducing confidence in these projections. © 2012. American Geophysical Union. All Rights Reserved. Source

Capotondi A.,National Oceanic and Atmospheric Administration | Capotondi A.,Climate Diagnostics Center
Geophysical Monograph Series

The temporal evolution and spatial pattern of the El Niño-Southern Oscillation (ENSO) is examined in seven state-of-the-art climate models in light of simple dynamical paradigms for ENSO. In general, the simulation of ENSO has improved in the present generation of climate models, with respect to previous generations, and the evolution of the upper ocean heat content is consistent with some of the leading dynamical paradigms. Unrealistic features of the model ENSO include the spatial structure of interannual sea surface temperature (SST) variations, as well as the time evolution of interannual variability. Standard deviations of interannual SST anomalies do not maximize close to the western coast of South America, as found in nature, and extend too far west along the equator. In most of the models included in this study, ENSO events occur more frequently and more regularly than they do in nature. The comparison of two climate models with different dominant ENSO time scales, one longer and closer to observations and the other much shorter than observed, shows that the spatial structure of the anomalous wind stress during ENSO events, in particular the meridional scale of the zonal wind stress anomalies, may play a key role in setting the ENSO time scale. Copyright © 2010 by the American Geophysical Union. Source

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