Robert Pasken - Academia.edu (original) (raw)
Papers by Robert Pasken
Dìqiú kēxué jíkān, 1993
Dual-Doppler data collected during the Ta iwan Area Mesoscale Experiment (TAMEX) were used to stu... more Dual-Doppler data collected during the Ta iwan Area Mesoscale Experiment (TAMEX) were used to study the kinetic energy balance of a subtropical prefrontal rainband over the Taiwan Strait. Fields of the system-relative wind and reflectivity were derived in a horizontal domain of 36 km by 40 km using the objective analysis scheme with 1-km grid spacing in all three directions, except in the lowest two levels where the height increment was chosen to be 0.5 km. There were ten analysis levels in the vertical ranging from 0.4 to 8.8 km. Vertical velocities were computed from the anelastic continuity equation by integrating downward with variational adjustment. Subsequently, fields of perturbation pressure and temperature were retrieved from a detailed wind field using the three momentum equations. The Doppler-derived winds and retrieved thermodynamic variables are then used to compute the magnitude of each term in the kinetic energy budget equation. Re sults show that the vertical total of the horizontal generation term acts as the main source of kinetic energy, while vertical totals of dissipation and the horizontal flux convergence/divergence of kinetic energy provide the main sinks. The horizontal flux convergence/divergence of kinetic energy is nearly balanced by the vertical flux conver gence/divergence at most levels. In a similar manner, the vertical generation of kinetic energy term is almost in balance with the total buoyancy term. The computed tendencies show the decrease of mean kinetic energy at low levels and the increase at middle levels, which are attributable to the generation and redistribution of kinetic energy and latent heat releases by organized convection associated with the rainband. These findings are consistent with the weakening of a low-level jet and the formation of a middle-level jet at the times of convection as revealed by upper air observations. The budget study further demonstrates that the storm's meso-7-scale environment is modified by areas of convection through scale interaction or "feedback" mechanisms.
Atmosphere
The total solar eclipse of 21 August 2017 was unique in that the path of totality swept across th... more The total solar eclipse of 21 August 2017 was unique in that the path of totality swept across the high spatial and temporal resolution QuantumWeather® mesonet and was very near the city of St. Louis Missouri. Thus, the meteorological response to the eclipse was complicated by the St. Louis urban heat island. Temperature changes of up 4 °C were observed across the network. Composite meteograms for rural, suburban, and urban stations displayed significant differences in the observed temperature and pressure response to the eclipse with a peak amplitude at the time of the eclipse. The differing response suggests that the urban heat island and changes in land surface characteristics alter the temperature and pressure response by the passage of the eclipse shadow. Oscillations in the composite meteograms appear to be the consequence of the passage of an outflow boundary across the network. As the outflow boundary moves north to south, the outflow boundary manifests its presence in the p...
The Pennsylvania State University/National Centers for Atmospheric Research Mesoscale Model Versi... more The Pennsylvania State University/National Centers for Atmospheric Research Mesoscale Model Version 5 (MM5) is employed to investigate the structure, evolution, and circulation of mid-western quasilinear meso-scale convective systems (MCSs) during the cool and/or transitional seasons. The model employs three domains with 9, 3, 1 and 0.3-km grid spacing, respectively. A “standard'' physical package was selected after running sensitivity tests. Two cases were chosen for this study. The first case is a classic transitional-season event in which the model predicted very well. The kinematic and dynamic structure of the simulated system, however, provided very detailed information as to how the model maintained a linear MCS some time after model initialization. The low-level simulated reflectivity fields show a strong similarity to the observations. Cross-sectional views show the detailed evolution occurring at different locations of the bowing segment of the squall line. Plan vie...
Introduction Many people experience a seasonal disorder that causes sneezing, itching, runny nose... more Introduction Many people experience a seasonal disorder that causes sneezing, itching, runny nose and nasal congestion. Seasonal allergic rhinitis, also known as "hay fever", affects approximately 35.9 million people in the United States (Nathan et al.; 1997). Although treatment is possible, the American Academy of Allergy, Asthma and Immunology (AAAAI) recommends the complete avoidance of the allergens. By altering their daily routine to avoid the times and places where the allergens are present, hay fever sufferers can reduce the need for treatment and allow medical personnel to create a more effective treatment plan. In order to accomplish this, the spatial and temporal distribution during the day of the allergens needs to be known. Currently the only information concerning the pollen and mold concentrations in the Saint Louis area comes from the Saint Louis County Department of Health. This County Department samples pollens and molds at a single site in Clayton, Missouri and provides the pollen and mold concentrations for the previous 24-hours during business days. Thus the only information available to the public are the mold and pollen counts for the previous 24 hours. Forecasting of pollen counts is a very difficult task. Most techniques fall into one of two categories; one method, known as the receptor-oriented technique, predicts the concentration without prior knowledge of the emission strengths, duration or diffusion by the atmosphere. This technique is the most commonly used forecast technique. A second method, known as the sourceoriented technique, requires knowledge of the source locations, emission rates, and duration and the structure of the meteorological boundary layer. The source oriented tecnique is not in common use because of the complexities of modeling the atmospheric boundary layer (ABL) on scales small enough to accurately reproduce the temporal and spatial variations of the pollen and mold sources. Developments in mesoscale and pollution modeling allow experiments with the sourceoriented technique to be conducted. The MM5 mesoscale model (Dudhia et al.; 2001) is now capable of making accurate forecasts with resolutions as fine as 1 km 2 and allows experimentation with various boundary layer prediction schemes. The Air Resources Laboratory's (ARL's) HYSPLIT_4 (Draxler and Hess; 1998) readily accepts as input the meteorological data from mesoscale models to compute the dispersion rate from the vertical diffusivity profile, wind shear and the horizontal deformation of the wind field. Combined with an understanding of the biology of the plants releasing the pollen, the sources of the allergens can be mapped both spatially and temporally. The use of high resolution mesoscale
Every hurricane season, roughly 50-60 tropical low-pressure disturbances exit the West Africa coa... more Every hurricane season, roughly 50-60 tropical low-pressure disturbances exit the West Africa coast and traverse westward across the Atlantic. Approximately one-fifth of these disturbances become tropical depressions, tropical storms, or hurricanes. One of the most difficult challenges facing tropical forecasters is how to differentiate which tropical disturbances will develop beyond an African Easterly Wave (AEW). Part of the answer to this question lies in the West African Monsoon, a seasonal reversal of wind that provides beneficial rainfall to the Sahel, a region bounded by the Sahara Desert to the north and a rainy belt to the south. This region includes Senegal, Mali, Mauritania, Niger, Burkina Faso, Chad, and Sudan. Most the time, dry winds blow out of the Sahara from the east or northeast. However, from June through September, southwesterly monsoon winds transport moist air from the tropical Atlantic over the Sahel causing heavy rains to fall closer to the southern edge of t...
International Journal of Applied Earth Observation and Geoinformation, 2018
Latest improvements in the resolution of atmospheric satellite sensors that measure chemical cons... more Latest improvements in the resolution of atmospheric satellite sensors that measure chemical constituents from space have led to enhanced detection of trace gases. This paper explores the use of sulfur dioxide (SO 2) level 2 dataset from OMI instrument, in conjunction with aerosol optical depth and Ångström exponent data from MODIS spectroradiometer, to estimate SO 2 loads under clear and turbid atmospheres. The spatial patterns of SO 2 loads in polluted atmospheric conditions are compared with a regional pollutant dispersion model (CALPUFF) and field observations near the Andes Peruvian city La Oroya, which is one of the most polluted places in the world. The efficacy of this methodology is further examined incorporating synchronous wind vectors. Results show that the spatial-temporal dynamics of OMI SO 2 is in agreement with field measurements and CALPUFF. The SO 2 satellite data obtained under optimal viewing conditions and clear skies are also compared with field observations. A correlation is found between in-situ measurements and OMI estimations. The correlation increases for days with predominantly fine aerosols when Ångström exponents are between 0.7 and 1. Moreover, pixel averaging techniques and low and high spatial frequency filtration, applied to OMI SO 2 data, results in a more reliable representation of the mean SO 2 plume. The paper concludes that anthropogenic SO 2 can be monitored from space, even for turbid sky conditions. This demonstrates the potential for the use of satellite products to improve the air quality prediction models.
Terrestrial, Atmospheric and Oceanic Sciences, 1993
Dual-Doppler data collected during the Ta iwan Area Mesoscale Experiment (TAMEX) were used to stu... more Dual-Doppler data collected during the Ta iwan Area Mesoscale Experiment (TAMEX) were used to study the kinetic energy balance of a subtropical prefrontal rainband over the Taiwan Strait. Fields of the system-relative wind and reflectivity were derived in a horizontal domain of 36 km by 40 km using the objective analysis scheme with 1-km grid spacing in all three directions, except in the lowest two levels where the height increment was chosen to be 0.5 km. There were ten analysis levels in the vertical ranging from 0.4 to 8.8 km. Vertical velocities were computed from the anelastic continuity equation by integrating downward with variational adjustment. Subsequently, fields of perturbation pressure and temperature were retrieved from a detailed wind field using the three momentum equations. The Doppler-derived winds and retrieved thermodynamic variables are then used to compute the magnitude of each term in the kinetic energy budget equation. Re sults show that the vertical total of the horizontal generation term acts as the main source of kinetic energy, while vertical totals of dissipation and the horizontal flux convergence/divergence of kinetic energy provide the main sinks. The horizontal flux convergence/divergence of kinetic energy is nearly balanced by the vertical flux conver gence/divergence at most levels. In a similar manner, the vertical generation of kinetic energy term is almost in balance with the total buoyancy term. The computed tendencies show the decrease of mean kinetic energy at low levels and the increase at middle levels, which are attributable to the generation and redistribution of kinetic energy and latent heat releases by organized convection associated with the rainband. These findings are consistent with the weakening of a low-level jet and the formation of a middle-level jet at the times of convection as revealed by upper air observations. The budget study further demonstrates that the storm's meso-7-scale environment is modified by areas of convection through scale interaction or "feedback" mechanisms.
Terrestrial, Atmospheric and Oceanic Sciences, 1996
Radar measurements obtained from both conventional and Doppler radars were used to study the life... more Radar measurements obtained from both conventional and Doppler radars were used to study the life cycle of a prefrontal convective rainband during TAMEX IOP 13 on 25 June 1987. The conventional radar data were available at 20-min intervals, while Doppler data were available at 7-min intervals. Additionally, surface observations at 30-min intervals taken from nine stations over the west coast and the Ta iwan Strait were also used for analysis to determine the approximate positions of the Mei-Yu front and the leading edge of the rainband (gust front). Results show that a prefrontal convective rain band formed in the vicinity of the Mei-Yu front when the system was located far north of the island. As the rainband moved slowly down the central west coast, it began to move away from the front as gust fronts were formed by cells at the leading edge of the system. The convective cells generated low-level cold outflows in the warm sector to the southeast of the front. Part of these cold outflows moved toward the southeast, interacting with the strong moisture-rich southwest monsoon flow to form a gust front. At the same time, the southwestern portion of the front, located 50-60 km west of the coast, continued to lift moist air, generating a new cell along the front. This new cell then traveled to the east at a more rapid speed following the prevailing westerly flow at low levels. It eventually merged with the main (old) cell, thereby prolonging the lifetime of the rainband. The analysis in this study, as a whole, further supports the conceptual model of this rainband reported in the study by Lin et al. (1992) using two volumes of dual-Doppler data obtained from CP-4 and TOGA (Tropical Ocean and Global Atmosphere).
Terrestrial, Atmospheric and Oceanic Sciences, 1990
A thermodynamic retrieval method was employed to investigate some stwctural features of a subtrop... more A thermodynamic retrieval method was employed to investigate some stwctural features of a subtropical squall line during IOP-2 ..
Meteorology and Atmospheric Physics, 2016
Your article is protected by copyright and all rights are held exclusively by Springer-Verlag Wie... more Your article is protected by copyright and all rights are held exclusively by Springer-Verlag Wien. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com".
Each year, about 50 African Easterly Waves (AEWs) move off the West African coast and traverse th... more Each year, about 50 African Easterly Waves (AEWs) move off the West African coast and traverse the tropical Atlantic. Of these 50 AEWs, ten to fifteen may develop into tropical storms and half of that number may develop into hurricanes. With an increase in the number and intensity of tropical cyclones in the Atlantic over the past few years, questions have arisen on the effects of the Saharan Air Layer (SAL) and its interaction with tropical cyclogenesis. It is known that when tropical cyclones interact with SAL they have a hard time sustaining development due to a decrease in moisture content, and an overabundance of cloud condensation nuclei (CCN). When tropical cyclones move away from the SAL, rapid intensification has been noted. Numerical simulations using the WRF in concert with the NAMMA data are being conducted to better understand the interaction of AEWs with the SAL For these studies to be useful, a measure of the simulation accuracy is needed. Multiple simulations using d...
Plant Disease, 2006
This special report demonstrates the feasibility of long-term prediction of intercontinental disp... more This special report demonstrates the feasibility of long-term prediction of intercontinental dispersal of Phakopsora pachyrhizi spores, the causal agent of the devastating Asian soybean rust (SBR) that invaded the continental United States in 2004. The climate-dispersion integrated model system used for the prediction is the combination of the particle transport and dispersion model (HYSPLIT_4) with the regional climate prediction model (MM5). The integrated model system predicts the trajectory and concentration of P. pachyrhizi spores based on three-dimensional wind advection and turbulent transport while incorporating simple viability criteria for aerial spores. The weather input of the model system is from a seasonal global climate prediction. The spore source strength and distribution were estimated from detected SBR disease severity and spread. The model system was applied to the known P. pachyrhizi spore dispersal between and within continents while focusing on the disease ent...
Dual-Doppler wind data at 1423 CST for the 8 June 1974 tornadic storm, obtained from the National... more Dual-Doppler wind data at 1423 CST for the 8 June 1974 tornadic storm, obtained from the National Severe Storms Laboratory, were used to test a method for recovering the perturbation pressure and virtual temperature fields from the derived three-dimensional wind field. The data were meticulously processed following the procedures discussed by Brown et.al. (1981). The domain of interest had horizontal dimensions of 26 (km) x 26 (km) and a vertical extent of 12 km. The horizontal winds, relative to the storm, were obtained on a grid with 1 km intervals using Barnes' objective analysis scheme. Gridded values of the vertical velocity were computed from the anelastic continuity equation by integrating downward from the storm's top. A variational integral constraint similar to that used by Ray et al. (1980) was used to adjust the computed vertical velocities. No additional filtering other than that inherent in the objective analysis scheme was made. Once the three dimensional wi...
International Journal of Applied Earth Observation and Geoinformation, 2021
Abstract Trees play an integral role in the “green” framework of an urban ecosystem. However, jus... more Abstract Trees play an integral role in the “green” framework of an urban ecosystem. However, just as they are beneficial to the environment, they can pose a significant risk to utility infrastructure networks, particularly in severe weather events. The objectives of this research were to explore the effect of scale and spatial variation on the relationships between trees and utility assets for vegetation-related power outages through the incorporation of remote sensing and geographic information system (GIS) analysis. Tree location and structural metrics derived from airborne Light Detection and Ranging (LiDAR) data were combined with regional utility network GIS data to test the prediction analysis capabilities of global and local statistics at multiple scales. Pearson’s correlation was carried out to examine the relationships between tree structure and utility asset variables to vegetation-related power outages, including the effect of the resolution, or grid-cell size, on those relationships. To test the performance of global and local regression modeling on outage prediction, ordinary least square (OLS) and geographically weighted regression (GWR) models were evaluated using four explanatory variables (utility wire length, utility pole count, tree canopy area, maximum tree height) at four different grid cell scales (50 m, 500 m, 1 km, 2 km). In general, Pearson’s correlation demonstrated the strongest positive relationship between explanatory variables and power outages when only aggregating 50-m grid cells exhibiting co-location of trees and utility assets to 2-km grid cells. Local regression models performed better than global models at all scales, with GWR producing the highest adjusted R2 and lowest Akaike information criterion (AIC) values of 0.955 and 3213, respectively. Additionally, the performance of OLS and GWR models increased with scale as both models produced the highest adjusted R2 at 2-km grid-cell scale. GWR model outputs demonstrated unique spatial patterning across the study area. This research demonstrated the effect of scale and spatial variation on regression analysis for the estimation of tree-related power outages.
In the morning hours of 29 June 1998, a line of severe convective storms traversed central Iowa, ... more In the morning hours of 29 June 1998, a line of severe convective storms traversed central Iowa, producing a wide swath of straight-line wind damage (several gusts exceeding 50 m s-1) and isolated weak-to-moderate intensity tornadoes (F0-F2). This quasi-linear convective system evolved into a severe squall line with three high-precipitation (HP) supercells and multiple well-defined mid-level mesocyclones embedded within it. Although scattered wind damage was reported across many sections of the entire line, this paper focuses on the evolution of one particularly active portion associated with a nearly continuous swath of severe straight-line winds and tornadic activity beginning 40 km northwest of Des Moines and extending through the metropolitan area. One of the embedded HP supercells contained several mid-level rotating centers that exhibited descending vortex characteristics between 1716 and 1806 UTC; their strongest cyclonic shears persisted at mid levels of the circulation. As ...
Each year, about 50 African Easterly Waves (AEWs) move off the West African coast and traverse th... more Each year, about 50 African Easterly Waves (AEWs) move off the West African coast and traverse the tropical Atlantic. Of these 50 AEWs, ten to fifteen may develop into tropical storms and half of that number may develop into hurricanes. With an increase in the number and intensity of tropical cyclones in the Atlantic over the past few years, questions have arisen on the effects of the Saharan Air Layer (SAL) and its interaction with tropical cyclogenesis. Observations of the interaction between developing tropical cyclones and the SAL have revealed an environment that is hostile to maintaining deep convection or organization due to a decrease in moisture content, and an overabundance of cloud condensation nuclei. When tropical cyclones move away from the SAL, rapid intensification has been noted. Numerical simulations using the WRF in concert with NAMMA data are being conducted to better understand the interaction of AEWs with the SAL For these studies to be useful, a measure of the...
Regional model MM5 for downscaling (Grell et al., 1993) HYSPLIT model for particle transport, dis... more Regional model MM5 for downscaling (Grell et al., 1993) HYSPLIT model for particle transport, dispersion, and dry/wet deposition (Draxler and Hess, 1998) NOAA's daily-observed rainfall data (ftp://ftpprd.ncep.noaa.gov) Monthly rainfall model for epidemic favorability (Del Ponte et al., 2005)
Meteorology and Atmospheric Physics, 2016
Dìqiú kēxué jíkān, 1993
Dual-Doppler data collected during the Ta iwan Area Mesoscale Experiment (TAMEX) were used to stu... more Dual-Doppler data collected during the Ta iwan Area Mesoscale Experiment (TAMEX) were used to study the kinetic energy balance of a subtropical prefrontal rainband over the Taiwan Strait. Fields of the system-relative wind and reflectivity were derived in a horizontal domain of 36 km by 40 km using the objective analysis scheme with 1-km grid spacing in all three directions, except in the lowest two levels where the height increment was chosen to be 0.5 km. There were ten analysis levels in the vertical ranging from 0.4 to 8.8 km. Vertical velocities were computed from the anelastic continuity equation by integrating downward with variational adjustment. Subsequently, fields of perturbation pressure and temperature were retrieved from a detailed wind field using the three momentum equations. The Doppler-derived winds and retrieved thermodynamic variables are then used to compute the magnitude of each term in the kinetic energy budget equation. Re sults show that the vertical total of the horizontal generation term acts as the main source of kinetic energy, while vertical totals of dissipation and the horizontal flux convergence/divergence of kinetic energy provide the main sinks. The horizontal flux convergence/divergence of kinetic energy is nearly balanced by the vertical flux conver gence/divergence at most levels. In a similar manner, the vertical generation of kinetic energy term is almost in balance with the total buoyancy term. The computed tendencies show the decrease of mean kinetic energy at low levels and the increase at middle levels, which are attributable to the generation and redistribution of kinetic energy and latent heat releases by organized convection associated with the rainband. These findings are consistent with the weakening of a low-level jet and the formation of a middle-level jet at the times of convection as revealed by upper air observations. The budget study further demonstrates that the storm's meso-7-scale environment is modified by areas of convection through scale interaction or "feedback" mechanisms.
Atmosphere
The total solar eclipse of 21 August 2017 was unique in that the path of totality swept across th... more The total solar eclipse of 21 August 2017 was unique in that the path of totality swept across the high spatial and temporal resolution QuantumWeather® mesonet and was very near the city of St. Louis Missouri. Thus, the meteorological response to the eclipse was complicated by the St. Louis urban heat island. Temperature changes of up 4 °C were observed across the network. Composite meteograms for rural, suburban, and urban stations displayed significant differences in the observed temperature and pressure response to the eclipse with a peak amplitude at the time of the eclipse. The differing response suggests that the urban heat island and changes in land surface characteristics alter the temperature and pressure response by the passage of the eclipse shadow. Oscillations in the composite meteograms appear to be the consequence of the passage of an outflow boundary across the network. As the outflow boundary moves north to south, the outflow boundary manifests its presence in the p...
The Pennsylvania State University/National Centers for Atmospheric Research Mesoscale Model Versi... more The Pennsylvania State University/National Centers for Atmospheric Research Mesoscale Model Version 5 (MM5) is employed to investigate the structure, evolution, and circulation of mid-western quasilinear meso-scale convective systems (MCSs) during the cool and/or transitional seasons. The model employs three domains with 9, 3, 1 and 0.3-km grid spacing, respectively. A “standard'' physical package was selected after running sensitivity tests. Two cases were chosen for this study. The first case is a classic transitional-season event in which the model predicted very well. The kinematic and dynamic structure of the simulated system, however, provided very detailed information as to how the model maintained a linear MCS some time after model initialization. The low-level simulated reflectivity fields show a strong similarity to the observations. Cross-sectional views show the detailed evolution occurring at different locations of the bowing segment of the squall line. Plan vie...
Introduction Many people experience a seasonal disorder that causes sneezing, itching, runny nose... more Introduction Many people experience a seasonal disorder that causes sneezing, itching, runny nose and nasal congestion. Seasonal allergic rhinitis, also known as "hay fever", affects approximately 35.9 million people in the United States (Nathan et al.; 1997). Although treatment is possible, the American Academy of Allergy, Asthma and Immunology (AAAAI) recommends the complete avoidance of the allergens. By altering their daily routine to avoid the times and places where the allergens are present, hay fever sufferers can reduce the need for treatment and allow medical personnel to create a more effective treatment plan. In order to accomplish this, the spatial and temporal distribution during the day of the allergens needs to be known. Currently the only information concerning the pollen and mold concentrations in the Saint Louis area comes from the Saint Louis County Department of Health. This County Department samples pollens and molds at a single site in Clayton, Missouri and provides the pollen and mold concentrations for the previous 24-hours during business days. Thus the only information available to the public are the mold and pollen counts for the previous 24 hours. Forecasting of pollen counts is a very difficult task. Most techniques fall into one of two categories; one method, known as the receptor-oriented technique, predicts the concentration without prior knowledge of the emission strengths, duration or diffusion by the atmosphere. This technique is the most commonly used forecast technique. A second method, known as the sourceoriented technique, requires knowledge of the source locations, emission rates, and duration and the structure of the meteorological boundary layer. The source oriented tecnique is not in common use because of the complexities of modeling the atmospheric boundary layer (ABL) on scales small enough to accurately reproduce the temporal and spatial variations of the pollen and mold sources. Developments in mesoscale and pollution modeling allow experiments with the sourceoriented technique to be conducted. The MM5 mesoscale model (Dudhia et al.; 2001) is now capable of making accurate forecasts with resolutions as fine as 1 km 2 and allows experimentation with various boundary layer prediction schemes. The Air Resources Laboratory's (ARL's) HYSPLIT_4 (Draxler and Hess; 1998) readily accepts as input the meteorological data from mesoscale models to compute the dispersion rate from the vertical diffusivity profile, wind shear and the horizontal deformation of the wind field. Combined with an understanding of the biology of the plants releasing the pollen, the sources of the allergens can be mapped both spatially and temporally. The use of high resolution mesoscale
Every hurricane season, roughly 50-60 tropical low-pressure disturbances exit the West Africa coa... more Every hurricane season, roughly 50-60 tropical low-pressure disturbances exit the West Africa coast and traverse westward across the Atlantic. Approximately one-fifth of these disturbances become tropical depressions, tropical storms, or hurricanes. One of the most difficult challenges facing tropical forecasters is how to differentiate which tropical disturbances will develop beyond an African Easterly Wave (AEW). Part of the answer to this question lies in the West African Monsoon, a seasonal reversal of wind that provides beneficial rainfall to the Sahel, a region bounded by the Sahara Desert to the north and a rainy belt to the south. This region includes Senegal, Mali, Mauritania, Niger, Burkina Faso, Chad, and Sudan. Most the time, dry winds blow out of the Sahara from the east or northeast. However, from June through September, southwesterly monsoon winds transport moist air from the tropical Atlantic over the Sahel causing heavy rains to fall closer to the southern edge of t...
International Journal of Applied Earth Observation and Geoinformation, 2018
Latest improvements in the resolution of atmospheric satellite sensors that measure chemical cons... more Latest improvements in the resolution of atmospheric satellite sensors that measure chemical constituents from space have led to enhanced detection of trace gases. This paper explores the use of sulfur dioxide (SO 2) level 2 dataset from OMI instrument, in conjunction with aerosol optical depth and Ångström exponent data from MODIS spectroradiometer, to estimate SO 2 loads under clear and turbid atmospheres. The spatial patterns of SO 2 loads in polluted atmospheric conditions are compared with a regional pollutant dispersion model (CALPUFF) and field observations near the Andes Peruvian city La Oroya, which is one of the most polluted places in the world. The efficacy of this methodology is further examined incorporating synchronous wind vectors. Results show that the spatial-temporal dynamics of OMI SO 2 is in agreement with field measurements and CALPUFF. The SO 2 satellite data obtained under optimal viewing conditions and clear skies are also compared with field observations. A correlation is found between in-situ measurements and OMI estimations. The correlation increases for days with predominantly fine aerosols when Ångström exponents are between 0.7 and 1. Moreover, pixel averaging techniques and low and high spatial frequency filtration, applied to OMI SO 2 data, results in a more reliable representation of the mean SO 2 plume. The paper concludes that anthropogenic SO 2 can be monitored from space, even for turbid sky conditions. This demonstrates the potential for the use of satellite products to improve the air quality prediction models.
Terrestrial, Atmospheric and Oceanic Sciences, 1993
Dual-Doppler data collected during the Ta iwan Area Mesoscale Experiment (TAMEX) were used to stu... more Dual-Doppler data collected during the Ta iwan Area Mesoscale Experiment (TAMEX) were used to study the kinetic energy balance of a subtropical prefrontal rainband over the Taiwan Strait. Fields of the system-relative wind and reflectivity were derived in a horizontal domain of 36 km by 40 km using the objective analysis scheme with 1-km grid spacing in all three directions, except in the lowest two levels where the height increment was chosen to be 0.5 km. There were ten analysis levels in the vertical ranging from 0.4 to 8.8 km. Vertical velocities were computed from the anelastic continuity equation by integrating downward with variational adjustment. Subsequently, fields of perturbation pressure and temperature were retrieved from a detailed wind field using the three momentum equations. The Doppler-derived winds and retrieved thermodynamic variables are then used to compute the magnitude of each term in the kinetic energy budget equation. Re sults show that the vertical total of the horizontal generation term acts as the main source of kinetic energy, while vertical totals of dissipation and the horizontal flux convergence/divergence of kinetic energy provide the main sinks. The horizontal flux convergence/divergence of kinetic energy is nearly balanced by the vertical flux conver gence/divergence at most levels. In a similar manner, the vertical generation of kinetic energy term is almost in balance with the total buoyancy term. The computed tendencies show the decrease of mean kinetic energy at low levels and the increase at middle levels, which are attributable to the generation and redistribution of kinetic energy and latent heat releases by organized convection associated with the rainband. These findings are consistent with the weakening of a low-level jet and the formation of a middle-level jet at the times of convection as revealed by upper air observations. The budget study further demonstrates that the storm's meso-7-scale environment is modified by areas of convection through scale interaction or "feedback" mechanisms.
Terrestrial, Atmospheric and Oceanic Sciences, 1996
Radar measurements obtained from both conventional and Doppler radars were used to study the life... more Radar measurements obtained from both conventional and Doppler radars were used to study the life cycle of a prefrontal convective rainband during TAMEX IOP 13 on 25 June 1987. The conventional radar data were available at 20-min intervals, while Doppler data were available at 7-min intervals. Additionally, surface observations at 30-min intervals taken from nine stations over the west coast and the Ta iwan Strait were also used for analysis to determine the approximate positions of the Mei-Yu front and the leading edge of the rainband (gust front). Results show that a prefrontal convective rain band formed in the vicinity of the Mei-Yu front when the system was located far north of the island. As the rainband moved slowly down the central west coast, it began to move away from the front as gust fronts were formed by cells at the leading edge of the system. The convective cells generated low-level cold outflows in the warm sector to the southeast of the front. Part of these cold outflows moved toward the southeast, interacting with the strong moisture-rich southwest monsoon flow to form a gust front. At the same time, the southwestern portion of the front, located 50-60 km west of the coast, continued to lift moist air, generating a new cell along the front. This new cell then traveled to the east at a more rapid speed following the prevailing westerly flow at low levels. It eventually merged with the main (old) cell, thereby prolonging the lifetime of the rainband. The analysis in this study, as a whole, further supports the conceptual model of this rainband reported in the study by Lin et al. (1992) using two volumes of dual-Doppler data obtained from CP-4 and TOGA (Tropical Ocean and Global Atmosphere).
Terrestrial, Atmospheric and Oceanic Sciences, 1990
A thermodynamic retrieval method was employed to investigate some stwctural features of a subtrop... more A thermodynamic retrieval method was employed to investigate some stwctural features of a subtropical squall line during IOP-2 ..
Meteorology and Atmospheric Physics, 2016
Your article is protected by copyright and all rights are held exclusively by Springer-Verlag Wie... more Your article is protected by copyright and all rights are held exclusively by Springer-Verlag Wien. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com".
Each year, about 50 African Easterly Waves (AEWs) move off the West African coast and traverse th... more Each year, about 50 African Easterly Waves (AEWs) move off the West African coast and traverse the tropical Atlantic. Of these 50 AEWs, ten to fifteen may develop into tropical storms and half of that number may develop into hurricanes. With an increase in the number and intensity of tropical cyclones in the Atlantic over the past few years, questions have arisen on the effects of the Saharan Air Layer (SAL) and its interaction with tropical cyclogenesis. It is known that when tropical cyclones interact with SAL they have a hard time sustaining development due to a decrease in moisture content, and an overabundance of cloud condensation nuclei (CCN). When tropical cyclones move away from the SAL, rapid intensification has been noted. Numerical simulations using the WRF in concert with the NAMMA data are being conducted to better understand the interaction of AEWs with the SAL For these studies to be useful, a measure of the simulation accuracy is needed. Multiple simulations using d...
Plant Disease, 2006
This special report demonstrates the feasibility of long-term prediction of intercontinental disp... more This special report demonstrates the feasibility of long-term prediction of intercontinental dispersal of Phakopsora pachyrhizi spores, the causal agent of the devastating Asian soybean rust (SBR) that invaded the continental United States in 2004. The climate-dispersion integrated model system used for the prediction is the combination of the particle transport and dispersion model (HYSPLIT_4) with the regional climate prediction model (MM5). The integrated model system predicts the trajectory and concentration of P. pachyrhizi spores based on three-dimensional wind advection and turbulent transport while incorporating simple viability criteria for aerial spores. The weather input of the model system is from a seasonal global climate prediction. The spore source strength and distribution were estimated from detected SBR disease severity and spread. The model system was applied to the known P. pachyrhizi spore dispersal between and within continents while focusing on the disease ent...
Dual-Doppler wind data at 1423 CST for the 8 June 1974 tornadic storm, obtained from the National... more Dual-Doppler wind data at 1423 CST for the 8 June 1974 tornadic storm, obtained from the National Severe Storms Laboratory, were used to test a method for recovering the perturbation pressure and virtual temperature fields from the derived three-dimensional wind field. The data were meticulously processed following the procedures discussed by Brown et.al. (1981). The domain of interest had horizontal dimensions of 26 (km) x 26 (km) and a vertical extent of 12 km. The horizontal winds, relative to the storm, were obtained on a grid with 1 km intervals using Barnes' objective analysis scheme. Gridded values of the vertical velocity were computed from the anelastic continuity equation by integrating downward from the storm's top. A variational integral constraint similar to that used by Ray et al. (1980) was used to adjust the computed vertical velocities. No additional filtering other than that inherent in the objective analysis scheme was made. Once the three dimensional wi...
International Journal of Applied Earth Observation and Geoinformation, 2021
Abstract Trees play an integral role in the “green” framework of an urban ecosystem. However, jus... more Abstract Trees play an integral role in the “green” framework of an urban ecosystem. However, just as they are beneficial to the environment, they can pose a significant risk to utility infrastructure networks, particularly in severe weather events. The objectives of this research were to explore the effect of scale and spatial variation on the relationships between trees and utility assets for vegetation-related power outages through the incorporation of remote sensing and geographic information system (GIS) analysis. Tree location and structural metrics derived from airborne Light Detection and Ranging (LiDAR) data were combined with regional utility network GIS data to test the prediction analysis capabilities of global and local statistics at multiple scales. Pearson’s correlation was carried out to examine the relationships between tree structure and utility asset variables to vegetation-related power outages, including the effect of the resolution, or grid-cell size, on those relationships. To test the performance of global and local regression modeling on outage prediction, ordinary least square (OLS) and geographically weighted regression (GWR) models were evaluated using four explanatory variables (utility wire length, utility pole count, tree canopy area, maximum tree height) at four different grid cell scales (50 m, 500 m, 1 km, 2 km). In general, Pearson’s correlation demonstrated the strongest positive relationship between explanatory variables and power outages when only aggregating 50-m grid cells exhibiting co-location of trees and utility assets to 2-km grid cells. Local regression models performed better than global models at all scales, with GWR producing the highest adjusted R2 and lowest Akaike information criterion (AIC) values of 0.955 and 3213, respectively. Additionally, the performance of OLS and GWR models increased with scale as both models produced the highest adjusted R2 at 2-km grid-cell scale. GWR model outputs demonstrated unique spatial patterning across the study area. This research demonstrated the effect of scale and spatial variation on regression analysis for the estimation of tree-related power outages.
In the morning hours of 29 June 1998, a line of severe convective storms traversed central Iowa, ... more In the morning hours of 29 June 1998, a line of severe convective storms traversed central Iowa, producing a wide swath of straight-line wind damage (several gusts exceeding 50 m s-1) and isolated weak-to-moderate intensity tornadoes (F0-F2). This quasi-linear convective system evolved into a severe squall line with three high-precipitation (HP) supercells and multiple well-defined mid-level mesocyclones embedded within it. Although scattered wind damage was reported across many sections of the entire line, this paper focuses on the evolution of one particularly active portion associated with a nearly continuous swath of severe straight-line winds and tornadic activity beginning 40 km northwest of Des Moines and extending through the metropolitan area. One of the embedded HP supercells contained several mid-level rotating centers that exhibited descending vortex characteristics between 1716 and 1806 UTC; their strongest cyclonic shears persisted at mid levels of the circulation. As ...
Each year, about 50 African Easterly Waves (AEWs) move off the West African coast and traverse th... more Each year, about 50 African Easterly Waves (AEWs) move off the West African coast and traverse the tropical Atlantic. Of these 50 AEWs, ten to fifteen may develop into tropical storms and half of that number may develop into hurricanes. With an increase in the number and intensity of tropical cyclones in the Atlantic over the past few years, questions have arisen on the effects of the Saharan Air Layer (SAL) and its interaction with tropical cyclogenesis. Observations of the interaction between developing tropical cyclones and the SAL have revealed an environment that is hostile to maintaining deep convection or organization due to a decrease in moisture content, and an overabundance of cloud condensation nuclei. When tropical cyclones move away from the SAL, rapid intensification has been noted. Numerical simulations using the WRF in concert with NAMMA data are being conducted to better understand the interaction of AEWs with the SAL For these studies to be useful, a measure of the...
Regional model MM5 for downscaling (Grell et al., 1993) HYSPLIT model for particle transport, dis... more Regional model MM5 for downscaling (Grell et al., 1993) HYSPLIT model for particle transport, dispersion, and dry/wet deposition (Draxler and Hess, 1998) NOAA's daily-observed rainfall data (ftp://ftpprd.ncep.noaa.gov) Monthly rainfall model for epidemic favorability (Del Ponte et al., 2005)
Meteorology and Atmospheric Physics, 2016