Onset and end of the rainy season in South America in observations and the ECHAM 4.5 atmospheric general circulation model
Rainfall in South America as simulated by a 24-ensemble member of the ECHAM 4.5 atmospheric general circulation model is compared and contrasted with observations (in areas in which data are available) for the period 1976-2001. Emphasis is placed on determining the onset and end of the rainy season,...
Guardado en:
| Autores principales: | , , , , , , , |
|---|---|
| Formato: | JOUR |
| Materias: | |
| Acceso en línea: | http://hdl.handle.net/20.500.12110/paper_08948755_v20_n10_p2037_Liebmann |
| Aporte de: |
| id |
todo:paper_08948755_v20_n10_p2037_Liebmann |
|---|---|
| record_format |
dspace |
| spelling |
todo:paper_08948755_v20_n10_p2037_Liebmann2023-10-03T15:42:11Z Onset and end of the rainy season in South America in observations and the ECHAM 4.5 atmospheric general circulation model Liebmann, B. Camargo, S.J. Seth, A. Marengo, J.A. Carvalho, L.M.V. Allured, D. Fu, R. Vera, C.S. Atmospheric movements Atmospheric temperature Computer simulation Oceanography Rain Atmospheric general circulation model Interannual variation Climatology annual variation atmospheric general circulation model climatology rainfall sea surface temperature wet season Brazil South America Rainfall in South America as simulated by a 24-ensemble member of the ECHAM 4.5 atmospheric general circulation model is compared and contrasted with observations (in areas in which data are available) for the period 1976-2001. Emphasis is placed on determining the onset and end of the rainy season, from which its length and rain rate are determined. It is shown that over large parts of the domain the onset and ending dates are well simulated by the model, with biases of less than 10 days. There is a tendency for model onset to occur early and ending to occur late, resulting in a simulated rainy season that is on average too long in many areas. The model wet season rain rate also tends to be larger than observed. To estimate the relative importance of errors in wet season length and rain rate in determining biases in the annual total, adjusted totals are computed by substituting both the observed climatological wet season length and rate for those of the model. Problems in the rain rate generally are more important than problems in the length. The wet season length and rain rate also contribute substantially to interannual variations in the annual total. These quantities are almost independent, and it is argued that they are each associated with different mechanisms. The observed onset dates almost always lie within the range of onset of the ensemble members, even in the areas with a large model onset bias. In some areas, though, the model does not perform well. In southern Brazil the model ensemble average onset always occurs in summer, whereas the observations show that winter is often the wettest period. Individual members, however, do occasionally show a winter rainfall peak. In southern Northeast Brazil the model has a more distinct rainy season than is observed. In the northwest Amazon the model annual cycle is shifted relative to that observed, resulting in a model bias. No interannual relationship between model and observed onset dates is expected unless onset in the model and observations has a mutual relationship with SST anomalies. In part of the near-equatorial Amazon, there does exist an interannual relationship between onset dates. Previous studies have shown that in this area there is a relationship between SST anomalies and variations in seasonal total rainfall. © 2007 American Meteorological Society. JOUR info:eu-repo/semantics/openAccess http://creativecommons.org/licenses/by/2.5/ar http://hdl.handle.net/20.500.12110/paper_08948755_v20_n10_p2037_Liebmann |
| institution |
Universidad de Buenos Aires |
| institution_str |
I-28 |
| repository_str |
R-134 |
| collection |
Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) |
| topic |
Atmospheric movements Atmospheric temperature Computer simulation Oceanography Rain Atmospheric general circulation model Interannual variation Climatology annual variation atmospheric general circulation model climatology rainfall sea surface temperature wet season Brazil South America |
| spellingShingle |
Atmospheric movements Atmospheric temperature Computer simulation Oceanography Rain Atmospheric general circulation model Interannual variation Climatology annual variation atmospheric general circulation model climatology rainfall sea surface temperature wet season Brazil South America Liebmann, B. Camargo, S.J. Seth, A. Marengo, J.A. Carvalho, L.M.V. Allured, D. Fu, R. Vera, C.S. Onset and end of the rainy season in South America in observations and the ECHAM 4.5 atmospheric general circulation model |
| topic_facet |
Atmospheric movements Atmospheric temperature Computer simulation Oceanography Rain Atmospheric general circulation model Interannual variation Climatology annual variation atmospheric general circulation model climatology rainfall sea surface temperature wet season Brazil South America |
| description |
Rainfall in South America as simulated by a 24-ensemble member of the ECHAM 4.5 atmospheric general circulation model is compared and contrasted with observations (in areas in which data are available) for the period 1976-2001. Emphasis is placed on determining the onset and end of the rainy season, from which its length and rain rate are determined. It is shown that over large parts of the domain the onset and ending dates are well simulated by the model, with biases of less than 10 days. There is a tendency for model onset to occur early and ending to occur late, resulting in a simulated rainy season that is on average too long in many areas. The model wet season rain rate also tends to be larger than observed. To estimate the relative importance of errors in wet season length and rain rate in determining biases in the annual total, adjusted totals are computed by substituting both the observed climatological wet season length and rate for those of the model. Problems in the rain rate generally are more important than problems in the length. The wet season length and rain rate also contribute substantially to interannual variations in the annual total. These quantities are almost independent, and it is argued that they are each associated with different mechanisms. The observed onset dates almost always lie within the range of onset of the ensemble members, even in the areas with a large model onset bias. In some areas, though, the model does not perform well. In southern Brazil the model ensemble average onset always occurs in summer, whereas the observations show that winter is often the wettest period. Individual members, however, do occasionally show a winter rainfall peak. In southern Northeast Brazil the model has a more distinct rainy season than is observed. In the northwest Amazon the model annual cycle is shifted relative to that observed, resulting in a model bias. No interannual relationship between model and observed onset dates is expected unless onset in the model and observations has a mutual relationship with SST anomalies. In part of the near-equatorial Amazon, there does exist an interannual relationship between onset dates. Previous studies have shown that in this area there is a relationship between SST anomalies and variations in seasonal total rainfall. © 2007 American Meteorological Society. |
| format |
JOUR |
| author |
Liebmann, B. Camargo, S.J. Seth, A. Marengo, J.A. Carvalho, L.M.V. Allured, D. Fu, R. Vera, C.S. |
| author_facet |
Liebmann, B. Camargo, S.J. Seth, A. Marengo, J.A. Carvalho, L.M.V. Allured, D. Fu, R. Vera, C.S. |
| author_sort |
Liebmann, B. |
| title |
Onset and end of the rainy season in South America in observations and the ECHAM 4.5 atmospheric general circulation model |
| title_short |
Onset and end of the rainy season in South America in observations and the ECHAM 4.5 atmospheric general circulation model |
| title_full |
Onset and end of the rainy season in South America in observations and the ECHAM 4.5 atmospheric general circulation model |
| title_fullStr |
Onset and end of the rainy season in South America in observations and the ECHAM 4.5 atmospheric general circulation model |
| title_full_unstemmed |
Onset and end of the rainy season in South America in observations and the ECHAM 4.5 atmospheric general circulation model |
| title_sort |
onset and end of the rainy season in south america in observations and the echam 4.5 atmospheric general circulation model |
| url |
http://hdl.handle.net/20.500.12110/paper_08948755_v20_n10_p2037_Liebmann |
| work_keys_str_mv |
AT liebmannb onsetandendoftherainyseasoninsouthamericainobservationsandtheecham45atmosphericgeneralcirculationmodel AT camargosj onsetandendoftherainyseasoninsouthamericainobservationsandtheecham45atmosphericgeneralcirculationmodel AT setha onsetandendoftherainyseasoninsouthamericainobservationsandtheecham45atmosphericgeneralcirculationmodel AT marengoja onsetandendoftherainyseasoninsouthamericainobservationsandtheecham45atmosphericgeneralcirculationmodel AT carvalholmv onsetandendoftherainyseasoninsouthamericainobservationsandtheecham45atmosphericgeneralcirculationmodel AT alluredd onsetandendoftherainyseasoninsouthamericainobservationsandtheecham45atmosphericgeneralcirculationmodel AT fur onsetandendoftherainyseasoninsouthamericainobservationsandtheecham45atmosphericgeneralcirculationmodel AT veracs onsetandendoftherainyseasoninsouthamericainobservationsandtheecham45atmosphericgeneralcirculationmodel |
| _version_ |
1782027960841142272 |