Bartonellosis is a vector-borne, highly fatal, emerging infectious disease in high mountain valle... more Bartonellosis is a vector-borne, highly fatal, emerging infectious disease in high mountain valleys of Peru and other Andean South American countries. In the acute phase of the disease, death may result in up to
Using the CPC (Climate Prediction Center) Merged Analysis of Precipitation product along with the... more Using the CPC (Climate Prediction Center) Merged Analysis of Precipitation product along with the Goddard Earth Observing System reanalysis and the Climate Analysis Center sea surface temperature (SST) data, we conduct a diagnostic study of the interannual and decadal scale variability of summer rainfall over South America. Results show three leading modes of rainfall variation identified with interannual, decadal, and long-term trend variability. Together, these modes explain more than half the total variance. The first mode is highly correlated with El Nino/southern oscillation (ENSO), showing severe drought over Northeast Brazil and copious rainfall over the Ecuador coast and the area of Uruguay-Southern Brazil in El Nino years. This pattern is attributed to the large scale zonal shift of the Walker circulation and local Hadley cell anomaly induced by positive (negative) SST anomaly over the eastern (western) equatorial Pacific. In El Nino years, two convective belts indicated by upper tropospheric velocity potential trough and mid-tropospheric rising motion, which are somewhat symmetric about the equator, extend toward the northeast and the southeast into the tropical North and South Atlantic respectively. Sandwiched between the ascent is a region of descending motion over Northeast Brazil. The southern branch of the anomalous Hadley cell is dynamically linked to the increase of rainfall over Uruguay-Southern Brazil. The regional response of anomalous circulation shows a stronger South American summer monsoon and an enhanced (weakened) subtropical high over the South Atlantic (South Pacific) Ocean. The decadal variation displays a meridional shift of the Intertropical Convergence Zone (ITCZ), which is tie to the anomalous cross-equatorial SST gradient over the Atlantic and the eastern Pacific. In conjunction with this mode is a large scale mass swing between the polar regions and midlatitudes in both hemispheres. Over the South Atlantic and the South Pacific, the changes of the strength of the subtropical high and the associated surface wind are dynamically consistent with the distribution of local SST anomalies, suggesting the importance of the atmospheric forcing in the decadal time scale. The decadal mode also presents a weak summer monsoon in its positive phase, which reduces the moisture supply from the equatorial Atlantic and the Amazon Basin and results in negative rainfall anomalies over the central Andes and Gran Chaco. The long-term trend shows decrease of rainfall from the northwest coast to the southeast subtropical region and a southward shift of Atlantic ITCZ that leads to increased rainfall over northern and eastern Brazil. Our result shows a close link of this mode to the observed SST warming trend over the subtropical South Atlantic and a remote connection to the interdecadal SST variation over the extratropical North Atlantic found in previous studies.
The consequences of climate variability on human health, especially for poor and medically unders... more The consequences of climate variability on human health, especially for poor and medically underserved populations, have received much attention in recent years. Some of the most severe health hazards induced by climate variability are epidemics of vector-borne infectious diseases. Entomologic studies have shown that insect vectors that transmit diseases, such as malaria, yellow fever, dengue, etc., are sensitive to temperature, humidity wind, and rainfall patterns, and therefore, their abundance is potentially influenced by climate variability. Because of its geographical location, the climate of tropical South America is strongly influenced by El Niño. The episodic outbreaks of various diseases in this region have been linked to the El Niño cycles. Yet, according to a report of the World Health Organization [1999], early results from South American epidemiological studies, which were based on the aggregated national disease data irrespective of the regional meteorological impacts, found no consistent correlation between the El Niño effect with the epidemics of malaria and yellow fever.
ABSTRACT Forecast errors exhibit the characteristics of approximations in simulating dynamical an... more ABSTRACT Forecast errors exhibit the characteristics of approximations in simulating dynamical and physical processes in models. The models are very complex and hence it is not always possible to identify the approximations responsible for any particular error pattern in forecasts. A comparison between the models' forecast performances can be valuable in isolating the causes of error patterns. Here a comparison of forecast errors in the AFGL and COLA models is made with the intent of identifying the causes of forecast errors. The two models are based on identical approximations in simulating the dynamical processes and only minor differences in parameterizations of the physical processes. Nine ten-day forecasts are made to study the error characteristics in the two models. The errors in the 500 mb geopotential height are negative in tropics and positive in extratropics. The temperatures at 850 mb are colder than observed in tropics and warmer than observed in extratropics. At 150 mb the temperatures are warmer than observed in tropics and colder than observed in extratropics. These qualitative error characteristics are not only common to these two models, but also they are common in the NMC, GFDL, and ECMWF forecast models. The difference in the error structure between the two models is the magnitude of the error in tropics. The tropical error in the AFGL model is larger than than in the COLA model.
The intraseasonal variation (ISV) in the 30-60 day band, also known as Madden-Julian oscillation ... more The intraseasonal variation (ISV) in the 30-60 day band, also known as Madden-Julian oscillation (MJO), has been studied for decades. Madden and Julian showed that the oscillation originated from the western Indian Ocean, propagated eastward, got enhanced over the maritime continent and weakened after passing over the dateline. Composite studies showed evidences of a signal in upper and lower level zonal wind propagating around the globe during an oscillation. Theoretical studies pointed out that the interaction with the warm ocean surface and the coupling with the convective and radiative processes in the atmosphere could manifest the oscillation, which propagates eastward via mutual feedbacks between the wave motions and the cumulus heating. Over tropical South America, no independent 30-60 day oscillation has been reported so far, despite that Amazon is the most distinct tropical convection center over the western hemisphere and the fluxes from its surface of tropical rainforests...
ABSTRACT Fig. 1 One-grid correlation of TRMM TMI rainfall at test sites of Caraz (a) and Cusco (b... more ABSTRACT Fig. 1 One-grid correlation of TRMM TMI rainfall at test sites of Caraz (a) and Cusco (b) with that over surroundings.
Eos, Transactions American Geophysical Union, 2002
Abstract The consequences of climate variability on human health, especially for poor and medical... more Abstract The consequences of climate variability on human health, especially for poor and medically underserved populations, have received much attention in recent years. Some of the most severe health hazards induced by climate variability are epidemics of vector-...
A recently improved version of the COLA GCM, which simulates the Indian monsoon circulation and p... more A recently improved version of the COLA GCM, which simulates the Indian monsoon circulation and precipitation pattern closely, together with snow data derived from SMMR observations, were used to investigate the effect of anomalous spring Eurasian snow cover on the interannual variability of the Indian summer monsoon. We have successfully simulated the observed evidence that excessive winter/spring Eurasian snow cover is associated with a delay in monsoon onset, weak monsoon circulation, and an extended monsoon withdrawal period. JJAS simulated precipitation shows a reduction of about one standard deviation of model natural variation over the Indian region as well as a significant increase over the eastern portion of China. A study of the physical mechanisms involved reveals: (1) Energy used in melting excessive snow reduces the surface temperature over a broad region centered on the Tibetan Plateau. Reduced surface sensible heat flux reduces the mid-tropospheric temperature gradien...
This study evaluates the intraseasonal variability associated with summer precipitation over Sout... more This study evaluates the intraseasonal variability associated with summer precipitation over South America in 14 coupled general circulation models (GCMs) participating in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). Eight years of each model’s twentieth-century climate simulation are analyzed. Two dominant intraseasonal bands associated with summer precipitation over South America are focused on: the 40- and the 22-day band. The results show that in the southern summer (November–April), most of the models underestimate seasonal mean precipitation over central-east Brazil, northeast Brazil, and the South Atlantic convergence zone (SACZ), while the Atlantic intertropical convergence zone (ITCZ) is shifted southward of its observed position. Most of the models capture both the 40- and 22-day band around Uruguay, but with less frequent active episodes than observed. The models also tend to underestimate the total intraseasonal (10–90 day), the 40...
ABSTRACT Forecast errors exhibit the characteristics of approximations in simulating dynamical an... more ABSTRACT Forecast errors exhibit the characteristics of approximations in simulating dynamical and physical processes in models. The models are very complex and hence it is not always possible to identify the approximations responsible for any particular error pattern in forecasts. A comparison between the models' forecast performances can be valuable in isolating the causes of error patterns. Here a comparison of forecast errors in the AFGL and COLA models is made with the intent of identifying the causes of forecast errors. The two models are based on identical approximations in simulating the dynamical processes and only minor differences in parameterizations of the physical processes. Nine ten-day forecasts are made to study the error characteristics in the two models. The errors in the 500 mb geopotential height are negative in tropics and positive in extratropics. The temperatures at 850 mb are colder than observed in tropics and warmer than observed in extratropics. At 150 mb the temperatures are warmer than observed in tropics and colder than observed in extratropics. These qualitative error characteristics are not only common to these two models, but also they are common in the NMC, GFDL, and ECMWF forecast models. The difference in the error structure between the two models is the magnitude of the error in tropics. The tropical error in the AFGL model is larger than than in the COLA model.
Bartonellosis is a vector-borne, highly fatal, emerging infectious disease in high mountain valle... more Bartonellosis is a vector-borne, highly fatal, emerging infectious disease in high mountain valleys of Peru and other Andean South American countries. In the acute phase of the disease, death may result in up to
Using the CPC (Climate Prediction Center) Merged Analysis of Precipitation product along with the... more Using the CPC (Climate Prediction Center) Merged Analysis of Precipitation product along with the Goddard Earth Observing System reanalysis and the Climate Analysis Center sea surface temperature (SST) data, we conduct a diagnostic study of the interannual and decadal scale variability of summer rainfall over South America. Results show three leading modes of rainfall variation identified with interannual, decadal, and long-term trend variability. Together, these modes explain more than half the total variance. The first mode is highly correlated with El Nino/southern oscillation (ENSO), showing severe drought over Northeast Brazil and copious rainfall over the Ecuador coast and the area of Uruguay-Southern Brazil in El Nino years. This pattern is attributed to the large scale zonal shift of the Walker circulation and local Hadley cell anomaly induced by positive (negative) SST anomaly over the eastern (western) equatorial Pacific. In El Nino years, two convective belts indicated by upper tropospheric velocity potential trough and mid-tropospheric rising motion, which are somewhat symmetric about the equator, extend toward the northeast and the southeast into the tropical North and South Atlantic respectively. Sandwiched between the ascent is a region of descending motion over Northeast Brazil. The southern branch of the anomalous Hadley cell is dynamically linked to the increase of rainfall over Uruguay-Southern Brazil. The regional response of anomalous circulation shows a stronger South American summer monsoon and an enhanced (weakened) subtropical high over the South Atlantic (South Pacific) Ocean. The decadal variation displays a meridional shift of the Intertropical Convergence Zone (ITCZ), which is tie to the anomalous cross-equatorial SST gradient over the Atlantic and the eastern Pacific. In conjunction with this mode is a large scale mass swing between the polar regions and midlatitudes in both hemispheres. Over the South Atlantic and the South Pacific, the changes of the strength of the subtropical high and the associated surface wind are dynamically consistent with the distribution of local SST anomalies, suggesting the importance of the atmospheric forcing in the decadal time scale. The decadal mode also presents a weak summer monsoon in its positive phase, which reduces the moisture supply from the equatorial Atlantic and the Amazon Basin and results in negative rainfall anomalies over the central Andes and Gran Chaco. The long-term trend shows decrease of rainfall from the northwest coast to the southeast subtropical region and a southward shift of Atlantic ITCZ that leads to increased rainfall over northern and eastern Brazil. Our result shows a close link of this mode to the observed SST warming trend over the subtropical South Atlantic and a remote connection to the interdecadal SST variation over the extratropical North Atlantic found in previous studies.
The consequences of climate variability on human health, especially for poor and medically unders... more The consequences of climate variability on human health, especially for poor and medically underserved populations, have received much attention in recent years. Some of the most severe health hazards induced by climate variability are epidemics of vector-borne infectious diseases. Entomologic studies have shown that insect vectors that transmit diseases, such as malaria, yellow fever, dengue, etc., are sensitive to temperature, humidity wind, and rainfall patterns, and therefore, their abundance is potentially influenced by climate variability. Because of its geographical location, the climate of tropical South America is strongly influenced by El Niño. The episodic outbreaks of various diseases in this region have been linked to the El Niño cycles. Yet, according to a report of the World Health Organization [1999], early results from South American epidemiological studies, which were based on the aggregated national disease data irrespective of the regional meteorological impacts, found no consistent correlation between the El Niño effect with the epidemics of malaria and yellow fever.
ABSTRACT Forecast errors exhibit the characteristics of approximations in simulating dynamical an... more ABSTRACT Forecast errors exhibit the characteristics of approximations in simulating dynamical and physical processes in models. The models are very complex and hence it is not always possible to identify the approximations responsible for any particular error pattern in forecasts. A comparison between the models' forecast performances can be valuable in isolating the causes of error patterns. Here a comparison of forecast errors in the AFGL and COLA models is made with the intent of identifying the causes of forecast errors. The two models are based on identical approximations in simulating the dynamical processes and only minor differences in parameterizations of the physical processes. Nine ten-day forecasts are made to study the error characteristics in the two models. The errors in the 500 mb geopotential height are negative in tropics and positive in extratropics. The temperatures at 850 mb are colder than observed in tropics and warmer than observed in extratropics. At 150 mb the temperatures are warmer than observed in tropics and colder than observed in extratropics. These qualitative error characteristics are not only common to these two models, but also they are common in the NMC, GFDL, and ECMWF forecast models. The difference in the error structure between the two models is the magnitude of the error in tropics. The tropical error in the AFGL model is larger than than in the COLA model.
The intraseasonal variation (ISV) in the 30-60 day band, also known as Madden-Julian oscillation ... more The intraseasonal variation (ISV) in the 30-60 day band, also known as Madden-Julian oscillation (MJO), has been studied for decades. Madden and Julian showed that the oscillation originated from the western Indian Ocean, propagated eastward, got enhanced over the maritime continent and weakened after passing over the dateline. Composite studies showed evidences of a signal in upper and lower level zonal wind propagating around the globe during an oscillation. Theoretical studies pointed out that the interaction with the warm ocean surface and the coupling with the convective and radiative processes in the atmosphere could manifest the oscillation, which propagates eastward via mutual feedbacks between the wave motions and the cumulus heating. Over tropical South America, no independent 30-60 day oscillation has been reported so far, despite that Amazon is the most distinct tropical convection center over the western hemisphere and the fluxes from its surface of tropical rainforests...
ABSTRACT Fig. 1 One-grid correlation of TRMM TMI rainfall at test sites of Caraz (a) and Cusco (b... more ABSTRACT Fig. 1 One-grid correlation of TRMM TMI rainfall at test sites of Caraz (a) and Cusco (b) with that over surroundings.
Eos, Transactions American Geophysical Union, 2002
Abstract The consequences of climate variability on human health, especially for poor and medical... more Abstract The consequences of climate variability on human health, especially for poor and medically underserved populations, have received much attention in recent years. Some of the most severe health hazards induced by climate variability are epidemics of vector-...
A recently improved version of the COLA GCM, which simulates the Indian monsoon circulation and p... more A recently improved version of the COLA GCM, which simulates the Indian monsoon circulation and precipitation pattern closely, together with snow data derived from SMMR observations, were used to investigate the effect of anomalous spring Eurasian snow cover on the interannual variability of the Indian summer monsoon. We have successfully simulated the observed evidence that excessive winter/spring Eurasian snow cover is associated with a delay in monsoon onset, weak monsoon circulation, and an extended monsoon withdrawal period. JJAS simulated precipitation shows a reduction of about one standard deviation of model natural variation over the Indian region as well as a significant increase over the eastern portion of China. A study of the physical mechanisms involved reveals: (1) Energy used in melting excessive snow reduces the surface temperature over a broad region centered on the Tibetan Plateau. Reduced surface sensible heat flux reduces the mid-tropospheric temperature gradien...
This study evaluates the intraseasonal variability associated with summer precipitation over Sout... more This study evaluates the intraseasonal variability associated with summer precipitation over South America in 14 coupled general circulation models (GCMs) participating in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). Eight years of each model’s twentieth-century climate simulation are analyzed. Two dominant intraseasonal bands associated with summer precipitation over South America are focused on: the 40- and the 22-day band. The results show that in the southern summer (November–April), most of the models underestimate seasonal mean precipitation over central-east Brazil, northeast Brazil, and the South Atlantic convergence zone (SACZ), while the Atlantic intertropical convergence zone (ITCZ) is shifted southward of its observed position. Most of the models capture both the 40- and 22-day band around Uruguay, but with less frequent active episodes than observed. The models also tend to underestimate the total intraseasonal (10–90 day), the 40...
ABSTRACT Forecast errors exhibit the characteristics of approximations in simulating dynamical an... more ABSTRACT Forecast errors exhibit the characteristics of approximations in simulating dynamical and physical processes in models. The models are very complex and hence it is not always possible to identify the approximations responsible for any particular error pattern in forecasts. A comparison between the models' forecast performances can be valuable in isolating the causes of error patterns. Here a comparison of forecast errors in the AFGL and COLA models is made with the intent of identifying the causes of forecast errors. The two models are based on identical approximations in simulating the dynamical processes and only minor differences in parameterizations of the physical processes. Nine ten-day forecasts are made to study the error characteristics in the two models. The errors in the 500 mb geopotential height are negative in tropics and positive in extratropics. The temperatures at 850 mb are colder than observed in tropics and warmer than observed in extratropics. At 150 mb the temperatures are warmer than observed in tropics and colder than observed in extratropics. These qualitative error characteristics are not only common to these two models, but also they are common in the NMC, GFDL, and ECMWF forecast models. The difference in the error structure between the two models is the magnitude of the error in tropics. The tropical error in the AFGL model is larger than than in the COLA model.
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