Papers by Roger Pielke Sr
A comparison between two Mesoscale models, Colorado State University Regional Atmospheric Modelin... more A comparison between two Mesoscale models, Colorado State University Regional Atmospheric Modeling System (RAMS) version 4.4 coupled with the Land-Ecosystem-Atmosphere Feedback Model (LEAF2) and Penn State/NCAR's Mesoscale Model (MM5) coupled with NOAH Land Surface Model, were conducted in order to assess the sensitivity of forecasted planetary boundary layer (PBL) variables to anomalous initial volumetric soil moisture conditions. The experiments were conducted using three synoptic events examined in a previous study: June 11, 17 and 22, 2006. For each event, one control run six additional simulations were conducted with RAMS and MM5. In each of the events, initial volumetric soil moisture was increased and decreased by 0.05, 0.10, and 0.15 m 3 m-3 with respect to the initial conditions in the control experiment. Each of the events was individually analyzed. Precipitation was generally increased and decreased with enhanced and reduced soil moisture, respectively. Overall, RAMS simulations presented a greater sensitivity and variability in precipitation and PBL parameters. It was found that equivalent potential temperature, vertical wind velocities, and latent and sensible heat flux were helpful in explaining precipitation accumulation and distribution.
Climatic Change, 2000
This essay discusses several issues that have been overlooked in the U.S. National and IPCC asses... more This essay discusses several issues that have been overlooked in the U.S. National and IPCC assessments. These include the effect on the climate system of anthropogenic land-use change, and the biological influence of enhanced concentrations of atmospheric carbon dioxide. Evidence is presented to demonstrate the important role of these human disturbances to the earth’s climate. Several hypotheses are proposed to test which are based on our research results. These include whether human-caused landscape change has an effect at all time scales on local, regional, and global climate that is at least as important as currently expected to be caused by the radiative effect of the anthropogenic doubling of the effective greenhouse gas concentrations. In addition, since landscape (and other atmosphere-surface) interactions involve complex, nonlinear feedbacks, accurate prediction of climate variables beyond seasonal time scales may not be possible. As an alternate paradigm, a vulnerability a...
Lecture Notes in Earth Sciences, 2009
Test and improve the ability of climate models to reproduce the observed vertical structure of fo... more Test and improve the ability of climate models to reproduce the observed vertical structure of forcing for a variety of locations and forcing conditions. Undertake research to characterize the dependence of climate response on the vertical structure of radiative forcing. Report global mean radiative forcing at both the surface and the top of the atmosphere in climate change assessments. Determine the Importance of Regional Variation in Radiative Forcing National Research Council Report PRIORITY RECOMMENDATIONS Use climate records to investigate relationships between regional radiative forcing (e.g., land use or aerosol changes) and climate response in the same region, other regions, and globally. Quantify and compare climate responses from regional radiative forcings in different climate models and on different timescales (e.g., seasonal, interannual), and report results in climate change assessments.
Tropical Montane Cloud Forests
Ecological changes observed at cloud forests in Monteverde, Costa Rica, including disappearance o... more Ecological changes observed at cloud forests in Monteverde, Costa Rica, including disappearance of anuran populations and expansion of bird and bat ranges to higher elevations has been linked to an increasing trend in dry season mist free days. Prior studies suggest that the increasing trend in dry season mist free days may be influence by both large scale climate change processes and also regional scale changes in land use. Preliminary investigations exploring the impact of land use on cloud formation indicated that drying and warming of boundary layer air in response to deforestation leads to increased cloud base heights. In the present study, numerical model experiments utilizing realistic land use scenarios and atmospheric conditions are used to further explore the impact of land use on orographic cloud formation. The Regional Atmospheric Modeling System (RAMS) is used to simulate orographic cloud formation during the time period of 1-14 March, 2003 in the Monteverde region for pristine, current and future land use scenarios. These simulations are initiated from the same atmospheric conditions and are subject to similar lateral boundary conditions. Comparisons against observations show that RAMS realistically simulate the nature of orographic cloud formation and boundary layer thermodynamics. Numerical simulations show that deforestation in the lowlands and premontane areas results in an increase in average cloud base heights and a consequent decrease in the areal extent of montane forests immersed in clouds. In the current and future land use scenarios, an increase in Bowen ratio and warmer, drier air is found over lowlands and premontane areas. The simulated differences in cloud formation and air mass thermodynamics are positively correlated to the amount of deforestation in the lowland and premontane regions.
Hydrology and Earth System Sciences, 2014
This study adopted a differential land-use/landcover (LULC) analysis to evaluate dam-triggered la... more This study adopted a differential land-use/landcover (LULC) analysis to evaluate dam-triggered landatmosphere interactions for a number of LULC scenarios. Two specific questions were addressed: (1) can damtriggered LULC heterogeneities modify surface and energy budget, which, in turn, change regional convergence and precipitation patterns? (2) How extensive is the modification in surface moisture and energy budget altered by damtriggered LULC changes occurring in different climate and terrain features? The Regional Atmospheric Modeling System (RAMS, version 6.0) was set up for two climatologically and topographically contrasting regions: the American River watershed (ARW), located in California, and the Owyhee River watershed (ORW), located in eastern Oregon. For the selected atmospheric river precipitation event of 29 December 1996 to 3 January 1997, simulations of three pre-defined LULC scenarios are performed. The definition of the scenarios are (1) the "control" scenario, representing the contemporary land use, (2) the "pre-dam" scenario, representing the natural landscape before the construction of the dams and (3) the "non-irrigation" scenario, representing the condition where previously irrigated landscape in the control is transformed to the nearby land-use type. Results indicated that the ARW energy and moisture fluxes were more extensively affected by dam-induced changes in LULC than the ORW. Both regions, however, displayed commonalities in the modification of land-atmosphere processes due to LULC changes, with the control-non-irrigation scenario creating more change than the control-pre-dam scenarios. These commonalities were: (1) the combination of a decrease in temperature (up to 0.15 • C) and an increase at dew point (up to 0.25 • C) was observed; (2) there was a larger fraction of energy partitioned to latent heat flux (up to 10 W m −2) that increased the amount of water vapor in the atmosphere and resulted in a larger convective available potential energy (CAPE); (3) low-level wind-flow variation was found to be responsible for pressure gradients that affected localized circulations, moisture advection and convergence. At some locations, an increase in wind speed up to 1.6 m s −1 maximum was observed; (4) there were also areas of well-developed vertical motions responsible for moisture transport from the surface to higher altitudes that enhanced precipitation patterns in the study regions.
Tellus A: Dynamic Meteorology and Oceanography, 2014
A comparison between two mesoscale models, Colorado State University Regional Atmospheric Modelin... more A comparison between two mesoscale models, Colorado State University Regional Atmospheric Modeling System (RAMS) version 4.4 coupled with the Land-EcosystemÁAtmosphere Feedback Model (LEAF2) and Penn State/NCAR's Mesoscale Model (MM5) coupled with NOAH Land Surface Model, was conducted in order to assess the sensitivity of forecasted planetary boundary layer (PBL) variables to anomalous initial volumetric soil moisture conditions. The experiments were conducted using three synoptic events: June 11, 17 and 22, 2006. For each event, one control run and six additional simulations were completed using RAMS and MM5. In each of the events, initial volumetric soil moisture was increased and decreased by 0.05, 0.10 and 0.15 m 3 m (3. Each of the events was individually analysed. Precipitation generally increased and decreased with enhanced and reduced soil moisture, respectively. Overall, RAMS simulations presented a greater sensitivity and variability in precipitation and PBL parameters. It was found that equivalent potential temperature, vertical wind velocities, and latent and sensible heat flux were helpful in explaining precipitation accumulation and distribution.
Reviews of Geophysics, 2001
This paper uses published work to demonstrate the link between surface moisture and heat fluxes a... more This paper uses published work to demonstrate the link between surface moisture and heat fluxes and cumulus convective rainfall. The Earth's surface role with respect to the surface energy and moisture budgets is examined. Changes in land‐surface properties are shown to influence the heat and moisture fluxes within the planetary boundary layer, convective available potential energy, and other measures of the deep cumulus cloud activity. The spatial structure of the surface heating, as influenced by landscape patterning, produces focused regions for deep cumulonimbus convection. In the tropics, and during midlatitude summers, deep cumulus convection has apparently been significantly altered as a result of landscape changes. These alterations in cumulus convection teleconnect to higher latitudes, which significantly alters the weather in those regions. The effect of tropical deforestation is most clearly defined in the winter hemisphere. In the context of climate, landscape proces...
Natural Hazards, 2007
Aerosols can affect the cloud-radiation feedback and the precipitation over the Indian monsoon re... more Aerosols can affect the cloud-radiation feedback and the precipitation over the Indian monsoon region. In this paper, we propose that another pathway by which aerosols can modulate the multi-scale aspect of Indian monsoons is by altering the land-atmosphere interactions. The nonlinear feedbacks due to aerosol/diffuse radiation on coupled interactions over the Indian monsoon region are studied by: (1) reviewing recent field measurements and modeling studies, (2) analyzing the MODIS and AERONET aerosol optical depth datasets, and (3) diagnosing the results from sensitivity experiments using a mesoscale modeling system. The results of this study suggest that the large magnitude of aerosol loading and its impact on land-atmosphere interactions can significantly influence the mesoscale monsoonal characteristics in the Indo-Ganges Basin.
Monthly Weather Review, 2004
On several occasions, winter freezes have wrought severe destruction on Florida agriculture. A se... more On several occasions, winter freezes have wrought severe destruction on Florida agriculture. A series of devastating freezes around the turn of the twentieth century, and again during the 1980s, were related to anomalies in the large-scale flow of the ocean-atmosphere system. During the twentieth century, substantial areas of wetlands in south Florida were drained and converted to agricultural land for winter fresh vegetable and sugarcane production. During this time, much of the citrus industry also was relocated to those areas to escape the risk of freeze farther to the north. The purpose of this paper is to present a modeling study designed to investigate whether the conversion of the wetlands to agriculture itself could have resulted in or exacerbated the severity of recent freezes in those agricultural areas of south Florida. For three recent freeze events, a pair of simulations was undertaken with the Regional Atmospheric Modeling System. One member of each pair employed land surface properties that represent pre-1900s (near natural) land cover, whereas the other member of each pair employed data that represent near-current land-use patterns as derived from analysis of Landsat data valid for 1992/93. These two different land cover datasets capture well the conversion of wetlands to agriculture in south Florida during the twentieth century. Use of current land surface properties resulted in colder simulated minimum temperatures and temperatures that remained below freezing for a longer period at locations of key agricultural production centers in south Florida that were once natural wetlands. Examination of time series of the surface energy budget from one of the cases reveals that when natural land cover is used, a persistent moisture flux from the underlying wetlands during the nighttime hours served to prevent the development of below-freezing temperatures at those same locations. When the model results were subjected to an important sensitivity factor, the depth of standing water in the wetlands, the outcome remained consistent. These results provide another example of the potential for humans to perturb the climate system in ways that can have severe socioeconomic consequences by altering the land surface alone.
Monthly Weather Review, 1997
A nonhydrostatic, three-dimensional version of the Colorado State University Regional Atmospheric... more A nonhydrostatic, three-dimensional version of the Colorado State University Regional Atmospheric Modeling System (CSU-RAMS) is used to deduce the processes responsible for the formation of drylines and the subsequent initiation of deep, moist dryline convection. A range of cumuliform cloud types are explicitly simulated along drylines on 15, 16, and 26 May 1991 in accordance with observations. In the simulations, narrow convergence bands along the dryline provide the lift to initiate deep moist convection. The thermally direct secondary convective boundary layer (CBL) circulations along the dryline are frontogenetic and solenoidally forced. Maximum updrafts reach 5 m s Ϫ1 and the bands are 3-9 km wide and 10-100 km or more in length. The updrafts penetrate and are decelerated by the overlying stable air above the CBL, reaching depths of about 2000 m in the cases studied. Moisture convergence along the mesoscale updraft bands destabilizes the local sounding to deep convection, while simultaneously decreasing the CIN to zero where storms subsequently develop. The lapse rates of vapor mixing ratio and potential temperature in the mesoscale updrafts are rather small, indicating that increases of the lifted condensation level (LCL) and level of free convection (LFC) due to mixing following the parcel motion are also small. Simulated convective clouds of all modes, including shallow forced cumulus and storms, develop in regions where the CIN ranges from zero up to the order of the peak kinetic energy of the boundary layer updraft and moisture is sufficiently deep to permit water saturation to develop in the boundary layer. The findings suggest that classic cloud models may not adequately simulate the early development of dryline storms due to their use of thermal bubbles to initiate convection and their assumption of a horizontally homogeneous environment. In contrast, cautious optimism may be warranted in regard to operational numerical prediction of drylines and the threat of attendant deep convection with mesoscale models.
Meteorology and Atmospheric Physics, 1992
This paper presents a range of applications of the Regional Atmospheric Modeling System (RAMS), a... more This paper presents a range of applications of the Regional Atmospheric Modeling System (RAMS), a comprehensive mesoscale meteorological modeling system. Applications discussed in this paper include large eddy simulations (LES) and simulations of thunderstorms, cumulus fields, mesoscale convective systems, mid-latitude cirrus clouds, winter storms, mechanically-and thermally-forced mesoscale systems, and mesoscale atmospheric dispersion. A summary of current RAMS options is also presented. Improvements to RAMS currently underway include refinements to the cloud radiation, cloud microphysics, cumulus, and surface soil/vegetative parameterization schemes, the parallelization of the code, development of a more versatile visualization capability, and research into meso-~-scale cumulus parameterization.
Journal of the Atmospheric Sciences, 1998
A case day, 11 October 1987, was chosen for simulation using the Regional Atmospheric Modeling Sy... more A case day, 11 October 1987, was chosen for simulation using the Regional Atmospheric Modeling System (RAMS). The day was unique from other ''golden'' days of the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) in that the surface wind speeds were light in terms of magnitude. Numerous datasets were used to initialize the meteorology, vegetation, canopy height, roughness length, topography, and soil properties. The simulation was performed using the RAMS nested grid feature. First, the large-scale flow reproduced by RAMS was evaluated against the observations taken during FIFE and archived data available at the National Center for Atmospheric Research. Next, a large-eddy simulation (LES) was integrated for a 6-h period starting at 1500 UTC 11 October 1987. FIFE surface flux and surface thermodynamic and dynamic data were then used to evaluate the LES. It was found that LES fluxes were in poor spatial agreement with the observations, although domain-averaged values were in good agreement. A technique for initializing the near-surface to surface soil moisture was then developed after finding a nearlinear relationship between 6-h averaged latent heat and the initial model-gridded soil moisture obtained from an objective analysis of field data. The LES was performed again using the new soil moisture obtained from the relationship. The evaluation showed significant improvement in the model's ability to represent spatial heterogeneity of surface fluxes present on 11 October 1987.
Journal of Hydrometeorology, 2003
Snow cover can significantly suppress daytime temperatures by increasing the surface albedo and l... more Snow cover can significantly suppress daytime temperatures by increasing the surface albedo and limiting the surface temperature to 0ЊC. The strength of this effect is dependent upon how well the snow can cover, or mask, the underlying surface. In regions where tall vegetation protrudes through a shallow layer of snow, the temperature-reducing effects of the snow will be suppressed since the protruding vegetation will absorb solar radiation and emit an upward turbulent heat flux. This means that an atmospheric model must have a reasonable representation of the land cover, as well as be able to correctly calculate snow depth, if an accurate simulation of surface heat fluxes, air temperatures, and boundary layer structure is to be made. If too much vegetation protrudes through the snow, then the surface sensible heat flux will be too large and the air temperatures will be too high. In this study four simulations are run with the Regional Atmospheric Modeling System (RAMS 4.30) for a snow event that occurred in 1988 over the Texas Panhandle. The first simulation, called the control, is run with the most realistic version of the current land cover and the results verified against both ground stations and aircraft data. Simulations 2 and 3 use the default methods of specifying land cover in RAMS 4.29 and RAMS 4.30, respectively. The significance of these variations in land-cover definition is then examined by comparing with the control run. Finally, the last simulation is run with the land cover defined as all short grass, the natural cover for the region. The results of this study indicate that variations in the land-cover specification can lead to differences in sensible heat flux over snow as large as 80 W m Ϫ2. These differences in sensible heat flux can then lead to differences in daytime temperatures of as much as 6ЊC. Also, the height of the afternoon boundary layer can vary by as much as 200-300 m. In addition, the results suggest that daytime temperatures are cooler over snow in the regions where short grass has been converted to cropland, while they appear to be warmer over regions where shrubs have increased.
Journal of Hydrometeorology, 2014
Understanding the impact of postdam climate feedbacks, resulting from land use/land cover (LULC) ... more Understanding the impact of postdam climate feedbacks, resulting from land use/land cover (LULC) variability, on modification of extreme precipitation (EP) remains a challenge for a twenty-first-century approach to dam design and operation. In this study, the Regional Atmospheric Modeling System (RAMS, version 6.0) was used, involving a number of predefined LULC scenarios to address the important question regarding dams and their impoundments: How sensitive are the hydroclimatology and terrain features of a region in modulating the postdam response of climate feedbacks to EP? The study region covered the Owyhee Dam/Reservoir on the Owyhee River watershed (ORW), located in eastern Oregon. A systematic perturbation of the relative humidity in the initial and boundary condition of the model was carried out to simulate EP. Among the different LULC scenarios used in the simulation over the ORW, irrigation expansion in the postdam era resulted in an increase in EP up to 6% in the 72-h pre...
Journal of Geophysical Research, 2009
Journal of Geophysical Research: Atmospheres, 2010
In studies dealing with the impact of land use changes on atmospheric processes, a key methodolog... more In studies dealing with the impact of land use changes on atmospheric processes, a key methodological step is the validation of simulated current conditions. However, regions lacking detailed atmospheric and land use data provide limited information with which to accurately generate control simulations. In this situation, the difference between baseline control simulations and different land use change simulations can be quite different owing to the quality of the atmospheric and land use data sets. Using multiple simulations at the Monteverde cloud forest region of Costa Rica as an example, we show that when a regional climate model is used to study the effect of land use change, it can produce distinctly different results at regional scales, depending on the amount of data available to run the climate simulations. We show that for the specific case of land use change impact studies, the simulation results are very sensitive to the prescribed atmospheric information (e.g., lateral ...
Journal of Geophysical Research, 2003
Recent studies have shown that there has been a reduction in dry season moisture input from direc... more Recent studies have shown that there has been a reduction in dry season moisture input from direct interception of cloud water and wind-blown mist at the lee edge of the Monteverde cloud forest, Costa Rica, since the mid 1970s. This reduction of moisture could be responsible for the population crashes of anurans observed in the region. It has been hypothesized that this behavior is a result of increases in cloud base height, linked to increased sea surface temperatures. In this study we present a complementary hypothesis, that deforestation upwind of the Monteverde cloud forest preserve is responsible for the observed changes in cloud base height. An automated cumulus cloud classification scheme extracts monthly spatial maps of the frequency of occurrence of cumulus cloudiness over Costa Rica from GOES 8 visible channel satellite imagery. We find that cumulus cloud formation in the morning hours over deforested regions is suppressed compared to forested areas. The degree of suppression appears to be related to the extent of deforestation. This difference in cloud formation between forested and deforested areas is a clear signal of land use change influencing the regional climate. Regional Atmospheric Modeling System numerical modeling simulations are used to explore the differences in cloud field characteristics over the lowland pasture and forest landscapes. Statistically significant differences in cloud base height and cloud thickness occur between the forest and pasture simulations. Clouds have higher base heights and are thinner over pasture landscapes than over forested ones. On the other hand, these simulations show no statistically significant differences in cloud top heights, cloud cover, mean cloud water mixing ratio, or cloud liquid water path between pasture and forest simulations. However, in the simulations there are enhanced sensible heat fluxes and reduced latent heat fluxes over pasture compared to forest. It is the drier and warmer air over pasture surfaces that results in the formation of elevated thinner clouds. This study suggests that deforestation results in warmer, drier air upwind of the Monteverde cloud forests and that this could influence the base height of orographic cloudbanks crucial to the region during the dry season.
Journal of Geophysical Research: Atmospheres, 1999
A climate version of the Regional Atmospheric Modeling System (RAMS) is used to simulate snow-rel... more A climate version of the Regional Atmospheric Modeling System (RAMS) is used to simulate snow-related land-atmosphere interactions in the Great Plains and Rocky Mountain regions of the United States. The availability of observed snow-distribution products allow snow-water-equivalent distribution data to be assimilated directly into the RAMS simulations. By performing two kinds of model integrations, one with and one without assimilating the snow-distribution observations, the differences between the model runs are used to highlight model deficiencies and limitations and thus identify areas of possible improvement in the atmospheric model. The need to simulate subgrid snow distributions is identified and addressed by implementing a snow submodel that accounts for subgrid variations in air temperature and precipitation. This subgrid snow model is found to significantly improve the model's simulation of snow-related processes.
Journal of Climate, 2007
Fifty-three years of the NCEP–NCAR Reanalysis I are dynamically downscaled using the Regional Atm... more Fifty-three years of the NCEP–NCAR Reanalysis I are dynamically downscaled using the Regional Atmospheric Modeling System (RAMS) to generate a regional climate model (RCM) climatology of the contiguous United States and Mexico. Data from the RAMS simulations are compared to the recently released North American Regional Reanalysis (NARR), as well as observed precipitation and temperature data. The RAMS simulations show the value added by using a RCM in a process study framework to represent North American summer climate beyond the driving global atmospheric reanalysis. Because of its enhanced representation of the land surface topography, the diurnal cycle of convective rainfall is present. This diurnal cycle largely governs the transitions associated with the evolution of the North American monsoon with regards to rainfall, the surface energy budget, and surface temperature. The lower frequency modes of convective rainfall, though weaker, account for rainfall variability at a remote...
International Journal of Climatology, 2013
ABSTRACTLand cover changes (LCCs) play an important role in the climate system. Research over rec... more ABSTRACTLand cover changes (LCCs) play an important role in the climate system. Research over recent decades highlights the impacts of these changes on atmospheric temperature, humidity, cloud cover, circulation, and precipitation. These impacts range from the local‐ and regional‐scale to sub‐continental and global‐scale. It has been found that the impacts of regional‐scale LCC in one area may also be manifested in other parts of the world as a climatic teleconnection. In light of these findings, this article provides an overview and synthesis of some of the most notable types of LCC and their impacts on climate. These LCC types include agriculture, deforestation and afforestation, desertification, and urbanization. In addition, this article provides a discussion on challenges to, and future research directions in, assessing the climatic impacts of LCC.
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Papers by Roger Pielke Sr