The Nevada Climate Change Portal (NCCP) has been developed with support from a large, 5-year (200... more The Nevada Climate Change Portal (NCCP) has been developed with support from a large, 5-year (2008-2013) NSF EPSCoR Research Infrastructure Improvement (RII) grant to provide data resources and computing support for scientists researching the long-term effects of climate change in Nevada. To achieve its goals, NCCP contains not only environmental datasets but also software tools and services created by Nevada computer engineers to help data acquisition and processing. One such tool is an original web application, entitled VISTED (Visualization Tool of Environmental Data), which enables data selection, extraction, download, conversion, and visualization. Currently, this tool operates on the output of a hindcast NCAR/WRF-based model developed by one of the coauthors at the Desert Research Institute, Nevada. This output contains daily values for six variables and extends over 30 years (1980–2009), so it is fairly large, and data operations like the ones above are needed by scientists w...
Resources Board " to evaluate several issues related to modeling the transport of dust from a lar... more Resources Board " to evaluate several issues related to modeling the transport of dust from a large area source (the Oceano Dunes) to a receptor site located a few kilometers downwind of the source." "A comprehensive and efficient inverse modeling framework is presented as a method for the calculation of wind flow over the Oceano Dune field and a means to apply back trajectory analysis to estimate dust flux, including a thorough testing against receptor observations.
Abstract. There are two fundamental mechanisms through which cirrus clouds form; homo- and hetero... more Abstract. There are two fundamental mechanisms through which cirrus clouds form; homo- and heterogeneous ice nucleation (henceforth hom and het). The relative contribution of each mechanism to ice crystal production often determines the microphysical and radiative properties of a cirrus cloud. This study attempts to estimate the radiative contribution of hom relative to het by constraining the cloud microphysics in a climate model to conform with satellite retrievals of cirrus cloud effective diameter De, where the sampled cirrus cloud base had a temperature T
Governments’ responses to the COVID-19 pandemic provide a unique opportunity to study the effects... more Governments’ responses to the COVID-19 pandemic provide a unique opportunity to study the effects of restricted socioeconomic activity on air quality. Here, we study the changes in air pollution levels during the lockdown in Medellín and its metropolitan area, Colombia, for periods with and without enhanced regional fire activity, considering the effects of meteorology using random forest and multiple linear regression methods. The lockdown measures, which reduced mean traffic volume by 70% compared to 2016–2019, resulted in reductions for PM2.5 (50–63%), PM10 (59–64%), NO (75–76%), NO2 (43–47%), and CO (40–47%), while O3 concentration increased by 19–22%. In contrast, when fire activity was high, the effects of the lockdown on air quality were shadowed by the long-range transport of biomass burning emissions, increasing fine particulate matter and ozone. This study shows that healthier levels are achievable through significant efforts from decision-makers and society. The results h...
Running the WRF model is very easy: just find a good computer, follow the tutorials, compile and ... more Running the WRF model is very easy: just find a good computer, follow the tutorials, compile and run. The real challenge is creating meaningful numerical experiments and critically evaluating the model output.
We investigated the accuracy of numerical weather prediction (NWP)-based global horizontal irradi... more We investigated the accuracy of numerical weather prediction (NWP)-based global horizontal irradiance (GHI) and clear-sky index forecasting over southern Nevada. Accurate forecasts of solar irradiance are required for electric utilities to economically integrate substantial amounts of solar power into their power generation portfolios. Solar irradiance forecasting can enhance the value of renewable energy by anticipating fluctuations in these variable resources. Summertime cloud variability depends largely on the combination of tropical and extratropical synoptic-scale forcing, most of which is observable, predictable, and highly related to the North American Monsoon moisture surge events. We used high-resolution realtime NWP output based on the weather and research forecasting (WRF) model to study the ability of the model to deliver day-ahead GHI and clear-sky index forecasts for a the National Renewable Energy Laboratory (NREL)-University of Nevada site, located in Las Vegas, Nevada. High-resolution forecast products were obtained from the Desert Research Institute (DRI) archived real-time numerical weather forecasting products. Results showed the importance of developing a sitespecific seasonal and weather-dependent model output statistics (MOS) approach to improving forecast accuracy, which removes the bias and reduces the overall relative root-meansquare error (rRMSE) of GHI by as much as 6%, when compared to the uncorrected model output; improving forecast accuracy is obtained by adding information that relates regional-scale circulation patterns driving cloudiness, hence irradiance variability to the target area. We show the seasonal dependence of the NWP forecast accuracy and demonstrate that intelligent weather functions provide a pathway to improve accuracy of solar forecasts further.
This study focuses on the mesoscale airflow along the eastern slopes of the Bolivian Andes near t... more This study focuses on the mesoscale airflow along the eastern slopes of the Bolivian Andes near the city of Santa Cruz. Here the orientation of the Andes changes from NW-SE to N-S (the so-called "Andean bend or elbow"). Here, observations from a NOAA WP-3D research aircraft, obtained during the recent South American Low-Level Jet EXperiment (SALLJEX), showed large horizontal wind gradients on many days and a pronounced mesoscale warm feature in the lower troposphere, associated with cloud-free conditions. The airflow that characterizes these conditions is associated with a northwesterly lower-troposphere wind regime known as the South American Low-Level (SALLJ). A mesoscale cyclonic vortex is also observed on the lee side of the Andean bend, called here the Andean bend eddy. This study explores the dynamics of the meanflow / topography interaction through analysis of the observations and with the aid of numerical simulations of the feature. The simulations are carried out with the WRF model, used with a grid spacing of ~5 km to model the mesoscale structure of the northwesterly flow around the Andean bend. The flow on February 7 th 2003 is analyzed with initial conditions from the NCEP Global Tropospheric Analysis (FNL). The flow simulations are compared with the WP-3D observations for general agreement. The likelihood for the development of internal gravity waves, wave breaking and baroclinic vertical vorticity generation is explored for this case study.
This study presents the climatology of the vertical structure of water vapor flux above the Sierr... more This study presents the climatology of the vertical structure of water vapor flux above the Sierra Nevada during significant cool season (November–April) precipitation events. Atmospheric river (AR) and non-AR events are analyzed to better understand the effect of this structure on precipitation patterns. Daily measurements of cool season precipitation at seven weather stations around the Tahoe basin from 1974 to 2012 and NCEP/CPC gridded daily precipitation analysis along the Sierra crest for the period 1948–2012 are examined. NCEP–NCAR reanalysis and soundings from Oakland are used to look at upper atmospheric conditions, including the presence of vapor transport by low- and midlevel jets on storm days as well as upstream static stability in relation to significant precipitation events. Key findings are as follows: 1) ARs play a disproportionately large role in generating Tahoe basin precipitation during the cool season; 2) strong midlevel vapor transport needs to occur in tandem ...
Predicting sharp hydroclimatic gradients in the complex terrain of the Great Basin can prove to b... more Predicting sharp hydroclimatic gradients in the complex terrain of the Great Basin can prove to be challenging because of the lack of climate observations that are gradient focused. Furthermore, evaluating gridded data products (GDPs) of climate in such environments for use in local hydroclimatic assessments is also challenging and typically ignored because of the lack of observations. In this study, independent Nevada Climate-Ecohydrological Assessment Network (NevCAN) observations of temperature, relative humidity, and precipitation collected along large altitudinal gradients of the Snake and Sheep mountain ranges from water-year 2012 (October–September) are utilized to evaluate four GDPs of different spatial resolutions: Parameter–Elevation Regressions on Independent Slopes Model (PRISM) 4 km, PRISM 800 m, Daymet 1 km, and a North American Land Data Assimilation System (NLDAS)–PRISM hybrid 4-km product. Inconsistencies and biases in precipitation measurements due to station sitin...
The main objective of the study was to investigate atmospheric and ocean interaction processes in... more The main objective of the study was to investigate atmospheric and ocean interaction processes in the western Pacific and, in particular, effects of significant ocean heat loss in the Kuroshio and Kuroshio Extension regions on the lower and upper atmosphere. It is yet to be determined how significant are these processes are on climate scales. The understanding of these processes led us also to development of the methodology of coupling the Weather and Research Forecasting model with the Parallel Ocean Program model for western Pacific regional weather and climate simulations. We tested NCARdeveloped research software Coupler 7 for coupling of the WRF and POP models and assessed its usability for regional-scale applications. We completed test simulations using the Coupler 7 framework, but implemented a standard WRF model code with options for both one-and two-way mode coupling. This type of coupling will allow us to seamlessly incorporate new WRF updates and versions in the future. We also performed a long-term WRF simulation (15 years) covering the entire North Pacific as well as high-resolution simulations of a case study which included extreme ocean heat losses in the Kuroshio and Kuroshio Extension regions. Since the extreme ocean heat loss occurs during winter cold air outbreaks (CAO), we simulated and analyzed a case study of a severe CAO event in January 2000 in detail. We found that the ocean heat loss induced by CAOs is amplified by additional advection from mesocyclones forming on the southern part of the Japan Sea. Large scale synoptic patterns with anomalously strong anticyclone over Siberia and Mongolia, deep Aleutian Low, and the Pacific subtropical ridge are a crucial setup for the CAO. It was found that the onset of the CAO is related to the breaking of atmospheric Rossby waves and vertical transport of vorticity that facilitates meridional advection. The study also indicates that intrinsic parameterization of the surface fluxes within the WRF model needs more evaluation and analysis.
The second annual Nevada Renewable Energy Consortium meeting took place at UNLV on August 20. The... more The second annual Nevada Renewable Energy Consortium meeting took place at UNLV on August 20. The meeting focused on the current three NVREC program areas: Solar, Biomass and Geothermal. Presentations were made by participating entities and a poster session followed.
This paper describes an algorithm to describe the distribution of cloud forests in the tropics us... more This paper describes an algorithm to describe the distribution of cloud forests in the tropics using Moderate-Resolution Imaging Spectroradiometer (MODIS) imagery. As an important component to global biodiversity, the conservation of tropical cloud forests is a ...
Colombia using regionalization and scaling concepts with the long-term flow field as the scaling ... more Colombia using regionalization and scaling concepts with the long-term flow field as the scaling variable. All data sets, methods, and results are included in HidroSIG, an available interactive hydrologic atlas of Colombia.
Two recent field programs have focused on describing aspects of low-level jets in the Americas. B... more Two recent field programs have focused on describing aspects of low-level jets in the Americas. Both programs have used NOAA WP-3D research aircraft to make mesoscale measurements about the jets, with the object of describing the 3-dimensional structure of the flow over relatively large areas. During both field programs the WP-3D was used as a probe, with the aircraft moving vertically while carrying out flight patterns that were mostly predetermined. The object was to describe both the horizontal structure of the jets while also describing the vertical variation of the flow. This involved trade-offs in the design of the flights. The SALLJEX flights sampled a deeper jet flow, necessitating greater vertical coverage and lesser horizontal resolution. The NAME flights were intended to sample a shallow jet that was confined in part by topography. This presentation summarizes the advantages and disadvantages of using the aircraft in a porpoising mode, with examples drawn from both experiments. The objective is to explain the benefits (and limitations) of the porpoising procedure and discuss how it may be employed most effectively.
Aim To explain the relationship between topography, prevailing winds and precipitation in order t... more Aim To explain the relationship between topography, prevailing winds and precipitation in order to identify regions with contrasting precipitation regimes and then compare floristic similarity among regions in the context of climate change. Location Eastern slope of the tropical Andes, South America. Methods We used information sources in the public domain to identify the relationship between geology, topography, prevailing wind patterns and precipitation. Areas with contrasting precipitation regimes were identified and compared for their floristic similarity. Results We identify spatially separate super-humid, humid and relatively dry regions on the eastern slope of the Andes and show how they are formed by the interaction of prevailing winds, diurnally varying atmospheric circulations and the local topography of the Andes. One key aspect related to the formation of these climatically distinct regions is the South American low-level jet (SALLJ), a relatively steady wind gyre that flows pole-ward along the eastern slopes of the Andes and is part of the gyre associated with the Atlantic trade winds that cross the Amazon Basin. The strongest winds of the SALLJ occur near the 'elbow of the Andes' at 18°S. Super-humid regions with mean annual precipitation greater than 3500 mm, are associated with a 'favourable' combination of topography, wind-flow orientation and local air circulation that favours ascent at certain hours of the day. Much drier regions, with mean annual precipitation less than 1500 mm, are associated with 'unfavourable' topographic orientation with respect to the mean winds and areas of reduced cloudiness produced by local breezes that moderate the cloudiness. We show the distribution of satelliteestimated frequency of cloudiness and offer hypotheses to explain the occurrence of these patterns and to explain regions of anomalously low precipitation in Bolivia and northern Peru. Floristic analysis shows that overall similarity among all circumscribed regions of this study is low; however, similarity among superhumid and humid regions is greater when compared with similarity among dry regions. Spatially separate areas with humid and super-humid precipitation regimes show similarity gradients that are correlated with latitude (proximity) and precipitation. Main conclusions The distribution of precipitation on the eastern slope of the Andes is not simply correlated with latitude, as is often assumed, but is the result of the interplay between wind and topography. Understanding the phenomena responsible for producing the observed precipitation patterns is important for mapping and modelling biodiversity, as well as for interpreting both past and future climate scenarios and the impact of climate change on biodiversity. Superhumid and dry regions have topographic characteristics that contribute to local
Previous studies based on ice cores and sediment samples collected along Andean Ice Caps and the ... more Previous studies based on ice cores and sediment samples collected along Andean Ice Caps and the South American Highplane (Altiplano) revealed the development of Paleolake Tauca during the late Pleistocene (15000-13000 BP). During its maximum expansion, the lake occupied an area of ~50% of the Altiplano basin. Motivated by understanding the role of lake-induced circulations on Altiplano climate transitions towards wetter conditions, numerical simulations were made using the Weather Research and Forecasting (WRF) model. In order to do so, combinations of paleolake/no-paleolake and moist/dry atmospheric conditions were analyzed. The results suggest that Paleolake Tauca produced a moister environment in the Altiplano with respect to the present through, enhancing nocturnal mesoscale circulations and rainfall. However, the intensity and distribution of rainfall appears to be modulated by the large-scale moisture field.
The Nevada Climate Change Portal (NCCP) has been developed with support from a large, 5-year (200... more The Nevada Climate Change Portal (NCCP) has been developed with support from a large, 5-year (2008-2013) NSF EPSCoR Research Infrastructure Improvement (RII) grant to provide data resources and computing support for scientists researching the long-term effects of climate change in Nevada. To achieve its goals, NCCP contains not only environmental datasets but also software tools and services created by Nevada computer engineers to help data acquisition and processing. One such tool is an original web application, entitled VISTED (Visualization Tool of Environmental Data), which enables data selection, extraction, download, conversion, and visualization. Currently, this tool operates on the output of a hindcast NCAR/WRF-based model developed by one of the coauthors at the Desert Research Institute, Nevada. This output contains daily values for six variables and extends over 30 years (1980–2009), so it is fairly large, and data operations like the ones above are needed by scientists w...
Resources Board " to evaluate several issues related to modeling the transport of dust from a lar... more Resources Board " to evaluate several issues related to modeling the transport of dust from a large area source (the Oceano Dunes) to a receptor site located a few kilometers downwind of the source." "A comprehensive and efficient inverse modeling framework is presented as a method for the calculation of wind flow over the Oceano Dune field and a means to apply back trajectory analysis to estimate dust flux, including a thorough testing against receptor observations.
Abstract. There are two fundamental mechanisms through which cirrus clouds form; homo- and hetero... more Abstract. There are two fundamental mechanisms through which cirrus clouds form; homo- and heterogeneous ice nucleation (henceforth hom and het). The relative contribution of each mechanism to ice crystal production often determines the microphysical and radiative properties of a cirrus cloud. This study attempts to estimate the radiative contribution of hom relative to het by constraining the cloud microphysics in a climate model to conform with satellite retrievals of cirrus cloud effective diameter De, where the sampled cirrus cloud base had a temperature T
Governments’ responses to the COVID-19 pandemic provide a unique opportunity to study the effects... more Governments’ responses to the COVID-19 pandemic provide a unique opportunity to study the effects of restricted socioeconomic activity on air quality. Here, we study the changes in air pollution levels during the lockdown in Medellín and its metropolitan area, Colombia, for periods with and without enhanced regional fire activity, considering the effects of meteorology using random forest and multiple linear regression methods. The lockdown measures, which reduced mean traffic volume by 70% compared to 2016–2019, resulted in reductions for PM2.5 (50–63%), PM10 (59–64%), NO (75–76%), NO2 (43–47%), and CO (40–47%), while O3 concentration increased by 19–22%. In contrast, when fire activity was high, the effects of the lockdown on air quality were shadowed by the long-range transport of biomass burning emissions, increasing fine particulate matter and ozone. This study shows that healthier levels are achievable through significant efforts from decision-makers and society. The results h...
Running the WRF model is very easy: just find a good computer, follow the tutorials, compile and ... more Running the WRF model is very easy: just find a good computer, follow the tutorials, compile and run. The real challenge is creating meaningful numerical experiments and critically evaluating the model output.
We investigated the accuracy of numerical weather prediction (NWP)-based global horizontal irradi... more We investigated the accuracy of numerical weather prediction (NWP)-based global horizontal irradiance (GHI) and clear-sky index forecasting over southern Nevada. Accurate forecasts of solar irradiance are required for electric utilities to economically integrate substantial amounts of solar power into their power generation portfolios. Solar irradiance forecasting can enhance the value of renewable energy by anticipating fluctuations in these variable resources. Summertime cloud variability depends largely on the combination of tropical and extratropical synoptic-scale forcing, most of which is observable, predictable, and highly related to the North American Monsoon moisture surge events. We used high-resolution realtime NWP output based on the weather and research forecasting (WRF) model to study the ability of the model to deliver day-ahead GHI and clear-sky index forecasts for a the National Renewable Energy Laboratory (NREL)-University of Nevada site, located in Las Vegas, Nevada. High-resolution forecast products were obtained from the Desert Research Institute (DRI) archived real-time numerical weather forecasting products. Results showed the importance of developing a sitespecific seasonal and weather-dependent model output statistics (MOS) approach to improving forecast accuracy, which removes the bias and reduces the overall relative root-meansquare error (rRMSE) of GHI by as much as 6%, when compared to the uncorrected model output; improving forecast accuracy is obtained by adding information that relates regional-scale circulation patterns driving cloudiness, hence irradiance variability to the target area. We show the seasonal dependence of the NWP forecast accuracy and demonstrate that intelligent weather functions provide a pathway to improve accuracy of solar forecasts further.
This study focuses on the mesoscale airflow along the eastern slopes of the Bolivian Andes near t... more This study focuses on the mesoscale airflow along the eastern slopes of the Bolivian Andes near the city of Santa Cruz. Here the orientation of the Andes changes from NW-SE to N-S (the so-called "Andean bend or elbow"). Here, observations from a NOAA WP-3D research aircraft, obtained during the recent South American Low-Level Jet EXperiment (SALLJEX), showed large horizontal wind gradients on many days and a pronounced mesoscale warm feature in the lower troposphere, associated with cloud-free conditions. The airflow that characterizes these conditions is associated with a northwesterly lower-troposphere wind regime known as the South American Low-Level (SALLJ). A mesoscale cyclonic vortex is also observed on the lee side of the Andean bend, called here the Andean bend eddy. This study explores the dynamics of the meanflow / topography interaction through analysis of the observations and with the aid of numerical simulations of the feature. The simulations are carried out with the WRF model, used with a grid spacing of ~5 km to model the mesoscale structure of the northwesterly flow around the Andean bend. The flow on February 7 th 2003 is analyzed with initial conditions from the NCEP Global Tropospheric Analysis (FNL). The flow simulations are compared with the WP-3D observations for general agreement. The likelihood for the development of internal gravity waves, wave breaking and baroclinic vertical vorticity generation is explored for this case study.
This study presents the climatology of the vertical structure of water vapor flux above the Sierr... more This study presents the climatology of the vertical structure of water vapor flux above the Sierra Nevada during significant cool season (November–April) precipitation events. Atmospheric river (AR) and non-AR events are analyzed to better understand the effect of this structure on precipitation patterns. Daily measurements of cool season precipitation at seven weather stations around the Tahoe basin from 1974 to 2012 and NCEP/CPC gridded daily precipitation analysis along the Sierra crest for the period 1948–2012 are examined. NCEP–NCAR reanalysis and soundings from Oakland are used to look at upper atmospheric conditions, including the presence of vapor transport by low- and midlevel jets on storm days as well as upstream static stability in relation to significant precipitation events. Key findings are as follows: 1) ARs play a disproportionately large role in generating Tahoe basin precipitation during the cool season; 2) strong midlevel vapor transport needs to occur in tandem ...
Predicting sharp hydroclimatic gradients in the complex terrain of the Great Basin can prove to b... more Predicting sharp hydroclimatic gradients in the complex terrain of the Great Basin can prove to be challenging because of the lack of climate observations that are gradient focused. Furthermore, evaluating gridded data products (GDPs) of climate in such environments for use in local hydroclimatic assessments is also challenging and typically ignored because of the lack of observations. In this study, independent Nevada Climate-Ecohydrological Assessment Network (NevCAN) observations of temperature, relative humidity, and precipitation collected along large altitudinal gradients of the Snake and Sheep mountain ranges from water-year 2012 (October–September) are utilized to evaluate four GDPs of different spatial resolutions: Parameter–Elevation Regressions on Independent Slopes Model (PRISM) 4 km, PRISM 800 m, Daymet 1 km, and a North American Land Data Assimilation System (NLDAS)–PRISM hybrid 4-km product. Inconsistencies and biases in precipitation measurements due to station sitin...
The main objective of the study was to investigate atmospheric and ocean interaction processes in... more The main objective of the study was to investigate atmospheric and ocean interaction processes in the western Pacific and, in particular, effects of significant ocean heat loss in the Kuroshio and Kuroshio Extension regions on the lower and upper atmosphere. It is yet to be determined how significant are these processes are on climate scales. The understanding of these processes led us also to development of the methodology of coupling the Weather and Research Forecasting model with the Parallel Ocean Program model for western Pacific regional weather and climate simulations. We tested NCARdeveloped research software Coupler 7 for coupling of the WRF and POP models and assessed its usability for regional-scale applications. We completed test simulations using the Coupler 7 framework, but implemented a standard WRF model code with options for both one-and two-way mode coupling. This type of coupling will allow us to seamlessly incorporate new WRF updates and versions in the future. We also performed a long-term WRF simulation (15 years) covering the entire North Pacific as well as high-resolution simulations of a case study which included extreme ocean heat losses in the Kuroshio and Kuroshio Extension regions. Since the extreme ocean heat loss occurs during winter cold air outbreaks (CAO), we simulated and analyzed a case study of a severe CAO event in January 2000 in detail. We found that the ocean heat loss induced by CAOs is amplified by additional advection from mesocyclones forming on the southern part of the Japan Sea. Large scale synoptic patterns with anomalously strong anticyclone over Siberia and Mongolia, deep Aleutian Low, and the Pacific subtropical ridge are a crucial setup for the CAO. It was found that the onset of the CAO is related to the breaking of atmospheric Rossby waves and vertical transport of vorticity that facilitates meridional advection. The study also indicates that intrinsic parameterization of the surface fluxes within the WRF model needs more evaluation and analysis.
The second annual Nevada Renewable Energy Consortium meeting took place at UNLV on August 20. The... more The second annual Nevada Renewable Energy Consortium meeting took place at UNLV on August 20. The meeting focused on the current three NVREC program areas: Solar, Biomass and Geothermal. Presentations were made by participating entities and a poster session followed.
This paper describes an algorithm to describe the distribution of cloud forests in the tropics us... more This paper describes an algorithm to describe the distribution of cloud forests in the tropics using Moderate-Resolution Imaging Spectroradiometer (MODIS) imagery. As an important component to global biodiversity, the conservation of tropical cloud forests is a ...
Colombia using regionalization and scaling concepts with the long-term flow field as the scaling ... more Colombia using regionalization and scaling concepts with the long-term flow field as the scaling variable. All data sets, methods, and results are included in HidroSIG, an available interactive hydrologic atlas of Colombia.
Two recent field programs have focused on describing aspects of low-level jets in the Americas. B... more Two recent field programs have focused on describing aspects of low-level jets in the Americas. Both programs have used NOAA WP-3D research aircraft to make mesoscale measurements about the jets, with the object of describing the 3-dimensional structure of the flow over relatively large areas. During both field programs the WP-3D was used as a probe, with the aircraft moving vertically while carrying out flight patterns that were mostly predetermined. The object was to describe both the horizontal structure of the jets while also describing the vertical variation of the flow. This involved trade-offs in the design of the flights. The SALLJEX flights sampled a deeper jet flow, necessitating greater vertical coverage and lesser horizontal resolution. The NAME flights were intended to sample a shallow jet that was confined in part by topography. This presentation summarizes the advantages and disadvantages of using the aircraft in a porpoising mode, with examples drawn from both experiments. The objective is to explain the benefits (and limitations) of the porpoising procedure and discuss how it may be employed most effectively.
Aim To explain the relationship between topography, prevailing winds and precipitation in order t... more Aim To explain the relationship between topography, prevailing winds and precipitation in order to identify regions with contrasting precipitation regimes and then compare floristic similarity among regions in the context of climate change. Location Eastern slope of the tropical Andes, South America. Methods We used information sources in the public domain to identify the relationship between geology, topography, prevailing wind patterns and precipitation. Areas with contrasting precipitation regimes were identified and compared for their floristic similarity. Results We identify spatially separate super-humid, humid and relatively dry regions on the eastern slope of the Andes and show how they are formed by the interaction of prevailing winds, diurnally varying atmospheric circulations and the local topography of the Andes. One key aspect related to the formation of these climatically distinct regions is the South American low-level jet (SALLJ), a relatively steady wind gyre that flows pole-ward along the eastern slopes of the Andes and is part of the gyre associated with the Atlantic trade winds that cross the Amazon Basin. The strongest winds of the SALLJ occur near the 'elbow of the Andes' at 18°S. Super-humid regions with mean annual precipitation greater than 3500 mm, are associated with a 'favourable' combination of topography, wind-flow orientation and local air circulation that favours ascent at certain hours of the day. Much drier regions, with mean annual precipitation less than 1500 mm, are associated with 'unfavourable' topographic orientation with respect to the mean winds and areas of reduced cloudiness produced by local breezes that moderate the cloudiness. We show the distribution of satelliteestimated frequency of cloudiness and offer hypotheses to explain the occurrence of these patterns and to explain regions of anomalously low precipitation in Bolivia and northern Peru. Floristic analysis shows that overall similarity among all circumscribed regions of this study is low; however, similarity among superhumid and humid regions is greater when compared with similarity among dry regions. Spatially separate areas with humid and super-humid precipitation regimes show similarity gradients that are correlated with latitude (proximity) and precipitation. Main conclusions The distribution of precipitation on the eastern slope of the Andes is not simply correlated with latitude, as is often assumed, but is the result of the interplay between wind and topography. Understanding the phenomena responsible for producing the observed precipitation patterns is important for mapping and modelling biodiversity, as well as for interpreting both past and future climate scenarios and the impact of climate change on biodiversity. Superhumid and dry regions have topographic characteristics that contribute to local
Previous studies based on ice cores and sediment samples collected along Andean Ice Caps and the ... more Previous studies based on ice cores and sediment samples collected along Andean Ice Caps and the South American Highplane (Altiplano) revealed the development of Paleolake Tauca during the late Pleistocene (15000-13000 BP). During its maximum expansion, the lake occupied an area of ~50% of the Altiplano basin. Motivated by understanding the role of lake-induced circulations on Altiplano climate transitions towards wetter conditions, numerical simulations were made using the Weather Research and Forecasting (WRF) model. In order to do so, combinations of paleolake/no-paleolake and moist/dry atmospheric conditions were analyzed. The results suggest that Paleolake Tauca produced a moister environment in the Altiplano with respect to the present through, enhancing nocturnal mesoscale circulations and rainfall. However, the intensity and distribution of rainfall appears to be modulated by the large-scale moisture field.
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