Eugene McCaul - Academia.edu (original) (raw)
Papers by Eugene McCaul
Prior parameter space studies of simulated deep convection are extended to embrace variations in ... more Prior parameter space studies of simulated deep convection are extended to embrace variations in the ambient temperature at the Lifted Condensation Level (LCL). Within the context of the parameter space study design, changes in LCL temperature are roughly equivalent to changes in the ambient precipitable water. Two series of simulations are conducted, one with a warm LCL that is associated with approximately 60 mm of precipitable water, and another with LCL temperatures 8 C cooler, so that PW is reduced to roughly 30 mm. The sets of simulations include tests of the impact of changes in the buoyancy and shear profile shapes and of changes in mixed and moist layer depths, all of which have been shown to be important in prior work. Simulations discussed here feature values of bulk convective available potential energy (CAPE) of 800, 2000, or 3200 Joules per kilogram, and a single semicircular hodograph having radius of 12 meters per second, but with variable vertical shear. The simulat...
The behavior of a convective storm is closely related to its ambient environment. In this paper, ... more The behavior of a convective storm is closely related to its ambient environment. In this paper, we explore the environments that produce "extreme" storm behaviors, namely, strong surface winds; copious amounts of precipitation (rain and hail); and strong low level rotation, related to tornadoes. The study focuses on a set of over 200 cloud-resolving numerical simulations, with the dominant storm in each simulation tracked and analyzed for up to 2 h. It is found that different environmental conditions are needed to produce different types of "extreme" behavior. For example, increased convective available potential energy (CAPE) typically causes the amount of hail produced to increase, but has relatively little effect on surface precipitation rates. The ambient precipitable water (PW) is found to have a greater impact on heavy rainfall than does CAPE. The storms with the strongest low level rotation exist in environments with low cloud bases and low, continental v...
Anticipating whether or not convective storms will produce heavy precipitation is a challenging f... more Anticipating whether or not convective storms will produce heavy precipitation is a challenging forecast problem. In this paper, we utilize a set of over 200 unique cloud-resolving numerical simulations to investigate vertical profiles of temperature, humidity, and wind that favor increased surface precipitation intensity. Strong correlations are found to exist between surface rain and hail mixing ratios and deep tropospheric wind shear, with greater shears frequently associated with better organized convection and more precipitation. Raising the height of the level of free convection (LFC) is also somewhat correlated with increased surface rain and hail, which is enhanced by greater updraft overturning efficiency compared to storms in low LFC environments. Storms in cooler environments having reduced amounts of precipitable water (PW) nevertheless display greater precipitation efficiency and thus produce almost as much precipitation as storms in warmer, moister environments with hi...
Monthly Weather Review, 1988
Experimental and theoretical studies were performed of atmospheric aerosol backscatter and atmosp... more Experimental and theoretical studies were performed of atmospheric aerosol backscatter and atmospheric dynamics with Doppler lidar as a primary tool. Activities include field and laboratory measurement and analysis efforts. The primary focus of activities related to understanding aerosol backscatter is the GLObal Backscatter Experiment (GLOBE) program. GLOBE is a multi-element effort designed toward developing a global aerosol model to describe tropospheric clean background backscatter conditions that Laser Atmospheric Wind Sounder (LAWS) is likely to encounter. Two survey missions were designed and flown in the NASA DC-8 in November 1989 and May to June 1990 over the remote Pacific Ocean, a region where backscatter values are low and where LAWS wind measurements could make a major contribution. The instrument complement consisted of pulsed and continuous-wave (CW) CO2 gas and solid state lidars measuring aerosol backscatter, optical particle counters measuring aerosol concentration...
Tropical Rainfall Measuring Mission (TRMM)lightning and precipitation observations have confirmed... more Tropical Rainfall Measuring Mission (TRMM)lightning and precipitation observations have confirmed the existence of a robust relationship between lightning flash rates and the amount of large precipitating ice hydrometeors in storms. This relationship is exploited, in conjunction with the capabilities of the Weather Research and Forecast (WRF) model, to forecast the threat of lightning from convective storms using the output fields from the model forecasts. The simulated vertical flux of graupel at -15C is used in this study as a proxy for charge separation processes and their associated lightning risk. Initial experiments using 6-h simulations are conducted for a number of case studies for which three-dimensional lightning validation data from the North Alabama Lightning Mapping Array are available. The WRF has been initialized on a 2 km grid using Eta boundary conditions, Doppler radar radial velocity and reflectivity fields, and METAR and ACARS data. An array of subjective and obj...
In support of the National Climate Assessment (NCA) program, satellite Lightning Imag- ing Sensor... more In support of the National Climate Assessment (NCA) program, satellite Lightning Imag- ing Sensor (LIS) data is used to estimate lightning nitrogen oxides (LNOx) production over the southern portion of the conterminous US. The total energy of each flash is estimated by analyzing the LIS optical event data associated with each flash (i.e., event radiance, event footprint area, and derivable event range). The LIS detects an extremely small fraction of the total flash energy; this fraction is assumed to be constant apart from the variability associated with the flash optical energy detected across the narrow (0.909 nm) LIS band. The estimate of total energy from each flash is converted to moles of LNOx production by assuming a chemical yield of 10 17 molecules Joule 1 . The LIS-inferred variable LNOx production from each flash is summed to obtain total LNOx production, and then appropriately enhanced to account for LIS detection efficiency and LIS view time. Annual geographical plots a...
A large set of three-dimensional cloud-resolving simulations is used to explore convective storm ... more A large set of three-dimensional cloud-resolving simulations is used to explore convective storm behavior in low CAPE, high shear environments, similar to those associated with tropical cyclones. While storms in these low CAPE regimes expectedly produce less hail than those in moderate and high CAPE, surprisingly, storms produce similar amounts of liquid precipitation regardless of the ambient CAPE. As highlighted in recent research, the survivability of storms in low CAPE (and high shear) is critically dependent on the low-level lapse rates, with steeper lapse rates preferred for storm persistence. Also, as environmental precipitable water (PW) is reduced, mid-level storm updrafts become stronger, and near-surface vertical vorticity increases, all other factors held equal. In tropical, high PW environments, it is found that reversible CAPE is superior to pseudoadiabatic CAPE in predictions of simulated updraft velocity using parcel theory. These findings highlight some of the uniqu...
This paper explores the influence of basic environmental parameters on mid-level and low-level vo... more This paper explores the influence of basic environmental parameters on mid-level and low-level vorticity production in a large set of simulated convective storms. Results show that the primary environmental conditions that increase midlevel vorticity are: substantial deep layer tropospheric wind shear; large amounts of convective available potential energy (CAPE); and a high level of free convection (LFC). These conditions are, to a significant degree, the same as those that enhance updraft velocity. About 79% of the interexperiment variance in midlevel vorticity can be attributed to the seven environmental parameters studied herein, when combined in a multiple linear regression form. Vorticity amounts near the surface are explained less well (64%), and are again correlated with stronger wind shear, but, contrary to vorticity aloft, with lower lifting condensation level (LCL) and LFC heights. Near-surface vorticity is also found to correlate strongly with low-level updraft intensity...
Relationships between environmental conditions and the precipitation characteristics of simulated... more Relationships between environmental conditions and the precipitation characteristics of simulated storms in a large eight-dimensional parameter space study are investigated. Specifically, we explore which environmental parameters are associated with the greatest production of rain and hail, both aloft and near the surface. The rainwater and hail mixing ratios for each experiment are averaged during the second hour of 2 h
ABSTRACT The NASA Marshall Space Flight Center Lightning Nitrogen Oxides Model (LNOM) is applied ... more ABSTRACT The NASA Marshall Space Flight Center Lightning Nitrogen Oxides Model (LNOM) is applied to August 2006 North Alabama Lightning Mapping Array (NALMA) data to estimate the (unmixed and otherwise environmentally unmodified) vertical source profile of lightning nitrogen oxides, NOx = NO + NO 2 . Data from the National Lightning Detection Network™ (NLDN) is also employed. This is part of a larger effort aimed at building a more realistic lightning NOx emissions inventory for use by the U.S. Environmental Protection Agency (EPA) Community Multiscale Air Quality (CMAQ) modeling system. Overall, special attention is given to several important lightning variables including: the frequency and geographical distribution of lightning in the vicinity of the NALMA network, lightning type (ground or cloud flash), lightning channel length, channel altitude, channel peak current, and the number of strokes per flash. Laboratory spark chamber results from the literature are used to convert 1-meter channel segments (that are located at a particular known altitude; i.e., air density) to NOx concentration. The resulting lightning NOx source profiles are discussed.
Geophysical Monograph Series, 1993
... 21, 1967 59 at 207 72.1 Chantilly, Virginia David 0000 UTC Sept. ... The hurricane CAPEs were... more ... 21, 1967 59 at 207 72.1 Chantilly, Virginia David 0000 UTC Sept. ... The hurricane CAPEs were, however, comparable in magnitude to those found by Barnes andStossmeister [1986] near the rainbands of a maritime hurricane. ...
Using results from a large set of three-dimensional cloud resolving model simulations, we investi... more Using results from a large set of three-dimensional cloud resolving model simulations, we investigate the sensitivity of storm outflows, downdrafts, and cold pools to background environmental conditions. The dominant right-moving storm in each of over 200 unique experiments is analyzed, and its properties averaged during the second hour of 2 h simulations, to assess the general relationships between storm outflow characteristics and environmental parameters. The strongest surface wind gusts and largest areas of outflow are produced when convective available potential energy (CAPE) and bulk tropospheric wind shear are large, these being environmental conditions that are hallmarks of vigorous, organized convection. Strong winds are also more widespread when the atmospheric precipitable water (PW) is large, which permits greater production of precipitation aloft, and when the lifted condensation level (LCL) is raised, allowing increased evaporation of falling hydrometeors in the downdr...
Monthly Weather Review, 1989
Prior parameter space studies of simulated deep convection are extended to embrace variations in ... more Prior parameter space studies of simulated deep convection are extended to embrace variations in the ambient temperature at the Lifted Condensation Level (LCL). Within the context of the parameter space study design, changes in LCL temperature are roughly equivalent to changes in the ambient precipitable water. Two series of simulations are conducted, one with a warm LCL that is associated with approximately 60 mm of precipitable water, and another with LCL temperatures 8 C cooler, so that PW is reduced to roughly 30 mm. The sets of simulations include tests of the impact of changes in the buoyancy and shear profile shapes and of changes in mixed and moist layer depths, all of which have been shown to be important in prior work. Simulations discussed here feature values of bulk convective available potential energy (CAPE) of 800, 2000, or 3200 Joules per kilogram, and a single semicircular hodograph having radius of 12 meters per second, but with variable vertical shear. The simulat...
The behavior of a convective storm is closely related to its ambient environment. In this paper, ... more The behavior of a convective storm is closely related to its ambient environment. In this paper, we explore the environments that produce "extreme" storm behaviors, namely, strong surface winds; copious amounts of precipitation (rain and hail); and strong low level rotation, related to tornadoes. The study focuses on a set of over 200 cloud-resolving numerical simulations, with the dominant storm in each simulation tracked and analyzed for up to 2 h. It is found that different environmental conditions are needed to produce different types of "extreme" behavior. For example, increased convective available potential energy (CAPE) typically causes the amount of hail produced to increase, but has relatively little effect on surface precipitation rates. The ambient precipitable water (PW) is found to have a greater impact on heavy rainfall than does CAPE. The storms with the strongest low level rotation exist in environments with low cloud bases and low, continental v...
Anticipating whether or not convective storms will produce heavy precipitation is a challenging f... more Anticipating whether or not convective storms will produce heavy precipitation is a challenging forecast problem. In this paper, we utilize a set of over 200 unique cloud-resolving numerical simulations to investigate vertical profiles of temperature, humidity, and wind that favor increased surface precipitation intensity. Strong correlations are found to exist between surface rain and hail mixing ratios and deep tropospheric wind shear, with greater shears frequently associated with better organized convection and more precipitation. Raising the height of the level of free convection (LFC) is also somewhat correlated with increased surface rain and hail, which is enhanced by greater updraft overturning efficiency compared to storms in low LFC environments. Storms in cooler environments having reduced amounts of precipitable water (PW) nevertheless display greater precipitation efficiency and thus produce almost as much precipitation as storms in warmer, moister environments with hi...
Monthly Weather Review, 1988
Experimental and theoretical studies were performed of atmospheric aerosol backscatter and atmosp... more Experimental and theoretical studies were performed of atmospheric aerosol backscatter and atmospheric dynamics with Doppler lidar as a primary tool. Activities include field and laboratory measurement and analysis efforts. The primary focus of activities related to understanding aerosol backscatter is the GLObal Backscatter Experiment (GLOBE) program. GLOBE is a multi-element effort designed toward developing a global aerosol model to describe tropospheric clean background backscatter conditions that Laser Atmospheric Wind Sounder (LAWS) is likely to encounter. Two survey missions were designed and flown in the NASA DC-8 in November 1989 and May to June 1990 over the remote Pacific Ocean, a region where backscatter values are low and where LAWS wind measurements could make a major contribution. The instrument complement consisted of pulsed and continuous-wave (CW) CO2 gas and solid state lidars measuring aerosol backscatter, optical particle counters measuring aerosol concentration...
Tropical Rainfall Measuring Mission (TRMM)lightning and precipitation observations have confirmed... more Tropical Rainfall Measuring Mission (TRMM)lightning and precipitation observations have confirmed the existence of a robust relationship between lightning flash rates and the amount of large precipitating ice hydrometeors in storms. This relationship is exploited, in conjunction with the capabilities of the Weather Research and Forecast (WRF) model, to forecast the threat of lightning from convective storms using the output fields from the model forecasts. The simulated vertical flux of graupel at -15C is used in this study as a proxy for charge separation processes and their associated lightning risk. Initial experiments using 6-h simulations are conducted for a number of case studies for which three-dimensional lightning validation data from the North Alabama Lightning Mapping Array are available. The WRF has been initialized on a 2 km grid using Eta boundary conditions, Doppler radar radial velocity and reflectivity fields, and METAR and ACARS data. An array of subjective and obj...
In support of the National Climate Assessment (NCA) program, satellite Lightning Imag- ing Sensor... more In support of the National Climate Assessment (NCA) program, satellite Lightning Imag- ing Sensor (LIS) data is used to estimate lightning nitrogen oxides (LNOx) production over the southern portion of the conterminous US. The total energy of each flash is estimated by analyzing the LIS optical event data associated with each flash (i.e., event radiance, event footprint area, and derivable event range). The LIS detects an extremely small fraction of the total flash energy; this fraction is assumed to be constant apart from the variability associated with the flash optical energy detected across the narrow (0.909 nm) LIS band. The estimate of total energy from each flash is converted to moles of LNOx production by assuming a chemical yield of 10 17 molecules Joule 1 . The LIS-inferred variable LNOx production from each flash is summed to obtain total LNOx production, and then appropriately enhanced to account for LIS detection efficiency and LIS view time. Annual geographical plots a...
A large set of three-dimensional cloud-resolving simulations is used to explore convective storm ... more A large set of three-dimensional cloud-resolving simulations is used to explore convective storm behavior in low CAPE, high shear environments, similar to those associated with tropical cyclones. While storms in these low CAPE regimes expectedly produce less hail than those in moderate and high CAPE, surprisingly, storms produce similar amounts of liquid precipitation regardless of the ambient CAPE. As highlighted in recent research, the survivability of storms in low CAPE (and high shear) is critically dependent on the low-level lapse rates, with steeper lapse rates preferred for storm persistence. Also, as environmental precipitable water (PW) is reduced, mid-level storm updrafts become stronger, and near-surface vertical vorticity increases, all other factors held equal. In tropical, high PW environments, it is found that reversible CAPE is superior to pseudoadiabatic CAPE in predictions of simulated updraft velocity using parcel theory. These findings highlight some of the uniqu...
This paper explores the influence of basic environmental parameters on mid-level and low-level vo... more This paper explores the influence of basic environmental parameters on mid-level and low-level vorticity production in a large set of simulated convective storms. Results show that the primary environmental conditions that increase midlevel vorticity are: substantial deep layer tropospheric wind shear; large amounts of convective available potential energy (CAPE); and a high level of free convection (LFC). These conditions are, to a significant degree, the same as those that enhance updraft velocity. About 79% of the interexperiment variance in midlevel vorticity can be attributed to the seven environmental parameters studied herein, when combined in a multiple linear regression form. Vorticity amounts near the surface are explained less well (64%), and are again correlated with stronger wind shear, but, contrary to vorticity aloft, with lower lifting condensation level (LCL) and LFC heights. Near-surface vorticity is also found to correlate strongly with low-level updraft intensity...
Relationships between environmental conditions and the precipitation characteristics of simulated... more Relationships between environmental conditions and the precipitation characteristics of simulated storms in a large eight-dimensional parameter space study are investigated. Specifically, we explore which environmental parameters are associated with the greatest production of rain and hail, both aloft and near the surface. The rainwater and hail mixing ratios for each experiment are averaged during the second hour of 2 h
ABSTRACT The NASA Marshall Space Flight Center Lightning Nitrogen Oxides Model (LNOM) is applied ... more ABSTRACT The NASA Marshall Space Flight Center Lightning Nitrogen Oxides Model (LNOM) is applied to August 2006 North Alabama Lightning Mapping Array (NALMA) data to estimate the (unmixed and otherwise environmentally unmodified) vertical source profile of lightning nitrogen oxides, NOx = NO + NO 2 . Data from the National Lightning Detection Network™ (NLDN) is also employed. This is part of a larger effort aimed at building a more realistic lightning NOx emissions inventory for use by the U.S. Environmental Protection Agency (EPA) Community Multiscale Air Quality (CMAQ) modeling system. Overall, special attention is given to several important lightning variables including: the frequency and geographical distribution of lightning in the vicinity of the NALMA network, lightning type (ground or cloud flash), lightning channel length, channel altitude, channel peak current, and the number of strokes per flash. Laboratory spark chamber results from the literature are used to convert 1-meter channel segments (that are located at a particular known altitude; i.e., air density) to NOx concentration. The resulting lightning NOx source profiles are discussed.
Geophysical Monograph Series, 1993
... 21, 1967 59 at 207 72.1 Chantilly, Virginia David 0000 UTC Sept. ... The hurricane CAPEs were... more ... 21, 1967 59 at 207 72.1 Chantilly, Virginia David 0000 UTC Sept. ... The hurricane CAPEs were, however, comparable in magnitude to those found by Barnes andStossmeister [1986] near the rainbands of a maritime hurricane. ...
Using results from a large set of three-dimensional cloud resolving model simulations, we investi... more Using results from a large set of three-dimensional cloud resolving model simulations, we investigate the sensitivity of storm outflows, downdrafts, and cold pools to background environmental conditions. The dominant right-moving storm in each of over 200 unique experiments is analyzed, and its properties averaged during the second hour of 2 h simulations, to assess the general relationships between storm outflow characteristics and environmental parameters. The strongest surface wind gusts and largest areas of outflow are produced when convective available potential energy (CAPE) and bulk tropospheric wind shear are large, these being environmental conditions that are hallmarks of vigorous, organized convection. Strong winds are also more widespread when the atmospheric precipitable water (PW) is large, which permits greater production of precipitation aloft, and when the lifted condensation level (LCL) is raised, allowing increased evaporation of falling hydrometeors in the downdr...
Monthly Weather Review, 1989