What controls the interannual variation of the wet season onsets over the Amazon?

Previous studies have established that sea surface temperature anomalies (SSTAs) in the tropical Pacific and Atlantic are the main forcing of the interannual variation of the wet season onsets in the Amazon. However, this variation appears to be complex and not uniquely determined by SSTAs. What causes such a complexity and to what extent the interannual variation of the wet season onsets is predictable remain unclear. This study suggests that such a complex relationship is the result of several competing processes, which are nonlinearly related to the SSTAs. In particular, three dry season conditions are crucial for determining interannual variation of the wet season onset. (i) A poleward shift of the Southern Hemisphere subtropical jet (SHSJ) over the South American sector, initiated from a wave train-like structure possibly forced by south central Pacific SST patterns, can prevent cold frontal systems from moving northward into the Amazon. This delays cold air incursion and results in late wet season onset over the southern Amazon. (ii) An anomalous anticyclonic center, which enhances westerly wind at 850 hPa over the southern Amazon and also the South American low-level jets, leads to moisture export from the southern Amazon to La Plata basin and reduces convective systems that provide elevated diabatic heating. (iii) Smaller convective available potential energy (CAPE) limits local thermodynamically driven convection. Based on the stepwise and partial least squares regressions, these three selected preseasonal conditions (Nino 4, SHSJ, and CAPE) can explain 57% of the total variance of the wet season onset.

[1]  V. Barros,et al.  The Relation between Sea Surface Temperature at the Subtropical South-Central Pacific and Precipitation in Southeastern South America , 2002 .

[2]  Stephen S. O. Burgess,et al.  Hydraulic redistribution in three Amazonian trees , 2005, Oecologia.

[3]  R. Dickinson,et al.  Impact of biomass burning aerosol on the monsoon circulation transition over Amazonia , 2009 .

[4]  G. Visconti,et al.  Effects of the PDO Phase on the Tropical Belt Width , 2012 .

[5]  R. Fu,et al.  Cross-Equatorial Flow and Seasonal Cycle of Precipitation over South America , 2002 .

[6]  Q. Fu,et al.  Poleward Shift of Subtropical Jets Inferred from Satellite-Observed Lower-Stratospheric Temperatures , 2011 .

[7]  R. Houze,et al.  The Tropical Dynamical Response to Latent Heating Estimates Derived from the TRMM Precipitation Radar , 2004 .

[8]  E. Davidson,et al.  The role of deep roots in the hydrological and carbon cycles of Amazonian forests and pastures , 1994, Nature.

[9]  R. Dickinson,et al.  Increased dry-season length over southern Amazonia in recent decades and its implication for future climate projection , 2013, Proceedings of the National Academy of Sciences.

[10]  J. Halverson,et al.  Modulation of convection in the southwestern Amazon basin by extratropical stationary fronts , 2002 .

[11]  D. Thompson,et al.  Observations of large-scale ocean-atmosphere interaction in the Southern Hemisphere , 2007 .

[12]  Ajit Subramaniam,et al.  Causes and impacts of the 2005 Amazon drought , 2008 .

[13]  M. Garstang,et al.  Cloud and rain processes in a biosphere-atmosphere interaction context in the Amazon Region , 2002 .

[14]  J. Lenters,et al.  On the Origin of the Bolivian High and Related Circulation Features of the South American Climate , 1997 .

[15]  J. Marengo,et al.  Interannual Variability of the Rainy Season and Rainfall in the Brazilian Amazon Basin , 2001 .

[16]  J. Carton,et al.  Decadal and interannual SST variability in the tropical Atlantic Ocean , 1996 .

[17]  T. L’Ecuyer,et al.  Spectral Retrieval of Latent Heating Profiles from TRMM PR data. Part 3; Moistening Estimates over Tropical Ocean Regions , 2007 .

[18]  J. Randerson,et al.  Forecasting Fire Season Severity in South America Using Sea Surface Temperature Anomalies , 2011, Science.

[19]  J. Shukla,et al.  On the Dynamics of Droughts in Northeast Brazil: Observations, Theory and Numerical Experiments with a General Circulation Model , 1981 .

[20]  W. Petersen,et al.  Intraseasonal Forcing of Convection and Lightning Activity in the Southern Amazon as a Function of Cross-Equatorial Flow , 2006 .

[21]  Gregory P. Asner,et al.  Tropical forest carbon assessment: integrating satellite and airborne mapping approaches , 2009 .

[22]  Ilana Wainer,et al.  Onset and End of the Rainy Season in the Brazilian Amazon Basin , 2001 .

[23]  R. R. Hocking.  The analysis and selection of variables in linear regression , 1976 .

[24]  Rong Fu,et al.  Influence of Cold Air Intrusions on the Wet Season Onset over Amazonia , 2006 .

[25]  V. Barros,et al.  Differences in El Nino Response over the Southern Hemisphere , 2004 .

[26]  R. Dickinson,et al.  How well can CMIP5 simulate precipitation and its controlling processes over tropical South America? , 2013, Climate Dynamics.

[27]  W. Sombroek.  Spatial and Temporal Patterns of Amazon Rainfall , 2001 .

[28]  S. Nigam,et al.  Residual Diagnosis of Diabatic Heating from ERA-40 and NCEP Reanalyses: Intercomparisons with TRMM , 2009 .

[29]  J. Marengo,et al.  Interannual variability of surface climate in the Amazon basin , 1992 .

[30]  W. Petersen,et al.  TRMM Observations of Intraseasonal Variability in Convective Regimes over the Amazon , 2002 .

[31]  V. Kousky.  Frontal Influences on Northeast Brazil , 1979 .

[32]  V. Kousky,et al.  The Southern Oscillation : oceanic-atmospheric circulation changes and related rainfall anomalies , 1983 .

[33]  C. Nobre,et al.  The Drought of Amazonia in 2005 , 2008 .

[34]  R. Fu,et al.  Influence of Cross-Andes Flow on the South American Low-Level Jet , 2004 .

[35]  J. Marengo,et al.  The drought of 2010 in the context of historical droughts in the Amazon region , 2011 .

[36]  C. Bretherton,et al.  The Effective Number of Spatial Degrees of Freedom of a Time-Varying Field , 1999 .

[37]  R. Reynolds,et al.  The NCEP/NCAR 40-Year Reanalysis Project , 1996, Renewable Energy.

[38]  W. Robinson.  On the midlatitude thermal response to tropical warmth , 2002 .

[39]  M. L’Heureux,et al.  Observed relationships between the El Niño-southern oscillation and the extratropical zonal-mean circulation , 2006 .

[40]  C. Hoyos,et al.  Changes in cloudiness over the Amazon rainforests during the last two decades: diagnostic and potential causes , 2011 .

[41]  Sarah M. Kang,et al.  Impact of Polar Ozone Depletion on Subtropical Precipitation , 2011, Science.

[42]  M. Novello,et al.  Geodesic motion and confinement in Gödel's universe , 1983 .

[43]  B. Liebmann,et al.  Daily Precipitation Grids for South America , 2005 .

[44]  C. Deser,et al.  Uncertainty in climate change projections: the role of internal variability , 2012, Climate Dynamics.

[45]  V. Kousky,et al.  An Improved Gridded Historical Daily Precipitation Analysis for Brazil , 2007 .

[46]  V. B. Rao,et al.  Annual variation of rainfall over Brazil and water vapor characteristics over South America , 1996 .

[47]  R. Fu,et al.  The influence of the land surface on the transition from dry to wet season in Amazonia , 2004 .

[48]  M. Hodnett,et al.  Control of Dry Season Evapotranspiration over the Amazonian Forest as Inferred from Observations at a Southern Amazon Forest Site , 2007 .

[49]  Ning Zeng,et al.  An Atlantic influence on Amazon rainfall , 2010 .

[50]  J. Neelin,et al.  Tropical drought regions in global warming and El Niño teleconnections , 2003 .

[51]  Celeste Saulo,et al.  Climatology of the Low-Level Jet East of the Andes as Derived from the NCEP–NCAR Reanalyses: Characteristics and Temporal Variability , 2004 .

[52]  R. Dickinson,et al.  How Do Tropical Sea Surface Temperatures Influence the Seasonal Distribution of Precipitation in the Equatorial Amazon , 2001 .

[53]  Paula K. Vigliarolo,et al.  Cold Season Synoptic-Scale Waves over Subtropical South America , 2002 .

[54]  R. Fu,et al.  Transition of the Large-Scale Atmospheric and Land Surface Conditions from the Dry to the Wet Season over Amazonia as Diagnosed by the ECMWF Re-Analysis , 2004 .

[55]  Scott M. Robeson,et al.  Daily Precipitation Grids for South America , 2006 .

[56]  Michel Tenenhaus,et al.  PLS path modeling , 2005, Comput. Stat. Data Anal..

[57]  P. Lawrence,et al.  Land use change exacerbates tropical South American drought by sea surface temperature variability , 2011 .

[58]  R. Garreaud.  Cold Air Incursions over Subtropical and Tropical South America: A Numerical Case Study , 1999 .

[59]  M. Allen,et al.  Sensitivity of Twentieth-Century Sahel Rainfall to Sulfate Aerosol and CO2 Forcing , 2011 .

[60]  John C. H. Chiang,et al.  Tropical tropospheric temperature variations caused by ENSO and their influence on the remote tropical climate , 2002 .

[61]  R. Garreaud,et al.  Cold Air Incursions over Subtropical South America: Mean Structure and Dynamics , 2000 .

[62]  Paula K. Vigliarolo,et al.  A Diagnostic Study of Cold-Air Outbreaks over South America , 2000 .

[63]  Luiz A. T. Machado,et al.  Seasonal and diurnal variability of convection over the Amazonia: A comparison of different vegetation types and large scale forcing , 2004 .

[64]  R. Seager,et al.  Mechanisms of Hemispherically Symmetric Climate Variability , 2003 .

[65]  M. Küttel,et al.  Winter warming in West Antarctica caused by central tropical Pacific warming , 2011 .

[66]  Edward J. Zipser,et al.  Recent developments on the South American monsoon system , 2012 .

[67]  D. Roy,et al.  Large seasonal swings in leaf area of Amazon rainforests , 2007, Proceedings of the National Academy of Sciences.

[68]  K. Mo,et al.  Interannual Variability in the Tropical Atlantic and Linkages to the Pacific , 2001 .

[69]  Thomas M. Smith,et al.  Improvements to NOAA’s Historical Merged Land–Ocean Surface Temperature Analysis (1880–2006) , 2008 .

[70]  R. Schnur,et al.  Climate-carbon cycle feedback analysis: Results from the C , 2006 .

[71]  I. S. Bowen.  The Ratio of Heat Losses by Conduction and by Evaporation from any Water Surface , 1926 .

[72]  William Finnegan,et al.  Modification of cirrus clouds to reduce global warming , 2009 .

[73]  Shoichi Shige,et al.  Spectral Retrieval of Latent Heating Profiles from TRMM PR Data. Part I: Development of a Model-Based Algorithm , 2004 .

[74]  R. Dickinson,et al.  Rainfall and its seasonality over the Amazon in the 21st century as assessed by the coupled models for the IPCC AR4 , 2006 .

[75]  T. Krishnamurti,et al.  Organization of convection and monsoon forecasts , 1998 .

[76]  D. Nepstad,et al.  Positive feedbacks in the fire dynamic of closed canopy tropical forests , 1999, Science.

[77]  W. Rossow,et al.  Structural Characteristics of Convective Systems over South America Related to Cold-Frontal Incursions , 2005 .

[78]  Bin Zhu,et al.  How do atmosphere and land surface influence seasonal changes of convection in the tropical Amazon , 1999 .

[79]  Robin T. Clarke,et al.  A comparison of extreme rainfall characteristics in the Brazilian Amazon derived from two gridded data sets and a national rain gauge network , 2010 .

[80]  Dong Eun Lee,et al.  North Tropical Atlantic influence on western Amazon fire season variability , 2011 .

[81]  B. Liebmann,et al.  Description of a complete (interpolated) outgoing longwave radiation dataset , 1996 .