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Abstract
Knowing the benefits of creating or expanding programs is important for determining optimal levels of investment. Yet estimates of the benefits of weather warning systems are sparse, perhaps because there is often no clear counterfactual of how individuals would have fared without a particular warning system. This paper enriches the literature and informs policy decisions by using conditional variation in the initial broadcast dates of the National Oceanic and Atmospheric Administration’s Weather Radio All Hazards (NWR) transmitters to produce both cross-sectional and fixed effects estimates of the causal impact of expanding the NWR transmitter network. Results suggest that from 1970 to 2014, expanding NWR coverage to a previously untreated county was associated with an almost 40% reduction in injuries and as much as a 50% reduction in fatalities. The benefits associated with further expansion of this system have likely declined over time.
Abstract
Knowing the benefits of creating or expanding programs is important for determining optimal levels of investment. Yet estimates of the benefits of weather warning systems are sparse, perhaps because there is often no clear counterfactual of how individuals would have fared without a particular warning system. This paper enriches the literature and informs policy decisions by using conditional variation in the initial broadcast dates of the National Oceanic and Atmospheric Administration’s Weather Radio All Hazards (NWR) transmitters to produce both cross-sectional and fixed effects estimates of the causal impact of expanding the NWR transmitter network. Results suggest that from 1970 to 2014, expanding NWR coverage to a previously untreated county was associated with an almost 40% reduction in injuries and as much as a 50% reduction in fatalities. The benefits associated with further expansion of this system have likely declined over time.
Abstract
Standard atmospheric energy budget computations are made for three distinct sets of Northern Hemisphere synoptic analyses prepared from data gathered during the August 1975 Data Systems Test. The first analysis set (System 1) included all data, the second (System 2) all but the satellite temperature retrievals (excepting some retained in the Southern Hemisphere for analysis model stability), and the third (System 3) all but the rawinsondes. Our results indicate that significant differences occur in the energetics of the analyses. In particular, there is a significant loss of longitudinal variance in an analysis based mainly on satellite retrievals as compared to that based mainly on rawinsonde data. In addition, forecasts by the NMC 6-layer numerical model initiated from System 1 and 2 analyses were evaluated for forecast periods from 00 to 72 h. It appears that this forecast model is sensitive to variations supplied by the initial data sets, but only to 12 h. Thereafter the forecast energetics are controlled by the model physics, and energy differences evolving from the different data sets remain constant in time.
Abstract
Standard atmospheric energy budget computations are made for three distinct sets of Northern Hemisphere synoptic analyses prepared from data gathered during the August 1975 Data Systems Test. The first analysis set (System 1) included all data, the second (System 2) all but the satellite temperature retrievals (excepting some retained in the Southern Hemisphere for analysis model stability), and the third (System 3) all but the rawinsondes. Our results indicate that significant differences occur in the energetics of the analyses. In particular, there is a significant loss of longitudinal variance in an analysis based mainly on satellite retrievals as compared to that based mainly on rawinsonde data. In addition, forecasts by the NMC 6-layer numerical model initiated from System 1 and 2 analyses were evaluated for forecast periods from 00 to 72 h. It appears that this forecast model is sensitive to variations supplied by the initial data sets, but only to 12 h. Thereafter the forecast energetics are controlled by the model physics, and energy differences evolving from the different data sets remain constant in time.
Abstract
The low-level atmospheric transformation associated with a class of traveling convective storms observed. over Venezuela is described. A strong low-level cooling is observed, confined mostly to the subcloud layer, and associated with a deeper layer of drying and acceleration of the easterly flow. A density current model is used to stratify the storm travel speeds, peak surface gusts and the accelerated flow at low levels behind the storm, and to relate these to the low-level flow ahead of the storm. There is reasonable agreement between these atmospheric data and laboratory observations of density currents. The updraft and down-draft structure is discussed using an interesting sounding cross section and trajectories from a three-dimensional numerical simulation. It appears that two distinct downdrafts exist: one driven by precipitation within the cumulonimbus cell, and a second mesoscale feature which is dynamically driven, and associated with descent over the spreading cold outflow.
Abstract
The low-level atmospheric transformation associated with a class of traveling convective storms observed. over Venezuela is described. A strong low-level cooling is observed, confined mostly to the subcloud layer, and associated with a deeper layer of drying and acceleration of the easterly flow. A density current model is used to stratify the storm travel speeds, peak surface gusts and the accelerated flow at low levels behind the storm, and to relate these to the low-level flow ahead of the storm. There is reasonable agreement between these atmospheric data and laboratory observations of density currents. The updraft and down-draft structure is discussed using an interesting sounding cross section and trajectories from a three-dimensional numerical simulation. It appears that two distinct downdrafts exist: one driven by precipitation within the cumulonimbus cell, and a second mesoscale feature which is dynamically driven, and associated with descent over the spreading cold outflow.
Abstract
Significant temporal variations in the “quasi-biennial” oscillation (QBO) of the equatorial stratosphere raise questions concerning relationships between the various characteristics of the oscillation. A comparison of observations made before 1962 with those made after 1962 suggests the following relationships: β ≈ PU /4 in the 10- to 30-mb layer; PU /8≤β≤PU /4 in the 30- to 50-mb layer; and cUPU ≈ constant from 10 to 50 mb (where β is the phase difference between the zonal wind-QBO and temperature-QBO, PU is the period of the zonal wind-QBO, and cU is the speed of vertical propagation of the zonal wind-QBO).
Abstract
Significant temporal variations in the “quasi-biennial” oscillation (QBO) of the equatorial stratosphere raise questions concerning relationships between the various characteristics of the oscillation. A comparison of observations made before 1962 with those made after 1962 suggests the following relationships: β ≈ PU /4 in the 10- to 30-mb layer; PU /8≤β≤PU /4 in the 30- to 50-mb layer; and cUPU ≈ constant from 10 to 50 mb (where β is the phase difference between the zonal wind-QBO and temperature-QBO, PU is the period of the zonal wind-QBO, and cU is the speed of vertical propagation of the zonal wind-QBO).
Abstract
The transport of water substance (ice and vapor) into the anvils of midlatitude continental thunderstorms is examined. Doppler radar reflectivity fields and horizontal and vertical windfields, in situ anvil measurements, and environmental soundings were used to estimate the anvil water mass flux for approximately five-minute intervals over one hour periods in six moderate to severe storms.
Vapor and ice mass fluxes into the anvil time-averaged for the study periods are about equal. Ratios of the time-averaged sums of these fluxes (A¯) to aircraft-derived cloud base influx (from Fankhauser) range from 18% to greater than 100%. Estimated accuracies are ±30 to 40%. Anvil fluxes exceed rainout at cloud base level as derived from radar reflectivity data by Fankhauser for half the storms.
It is shown that influx values alone are not reliable predictors of total storm condensation rates. The water mass storage term is evaluated and is found to be unimportant in relation to influx for all but one storm studied. Both A¯/influx and A¯/ rainout are highly correlated with the vertical shear of the horizontal winds.
Changes in the ice mass flux in the anvil with respect to altitude and distance from the updraft imply the absence of mesoscale ascent in the anvil.
Abstract
The transport of water substance (ice and vapor) into the anvils of midlatitude continental thunderstorms is examined. Doppler radar reflectivity fields and horizontal and vertical windfields, in situ anvil measurements, and environmental soundings were used to estimate the anvil water mass flux for approximately five-minute intervals over one hour periods in six moderate to severe storms.
Vapor and ice mass fluxes into the anvil time-averaged for the study periods are about equal. Ratios of the time-averaged sums of these fluxes (A¯) to aircraft-derived cloud base influx (from Fankhauser) range from 18% to greater than 100%. Estimated accuracies are ±30 to 40%. Anvil fluxes exceed rainout at cloud base level as derived from radar reflectivity data by Fankhauser for half the storms.
It is shown that influx values alone are not reliable predictors of total storm condensation rates. The water mass storage term is evaluated and is found to be unimportant in relation to influx for all but one storm studied. Both A¯/influx and A¯/ rainout are highly correlated with the vertical shear of the horizontal winds.
Changes in the ice mass flux in the anvil with respect to altitude and distance from the updraft imply the absence of mesoscale ascent in the anvil.
Abstract
Radar and surface thunderstorm data in North Dakota were investigated to obtain the climatology of thunderstorms in the state. A life cycle analysis for the individual storm cells between 2002 and 2006 was carried out, and it was found that June and July were the peak months, late afternoon to early morning was the peak time for thunderstorms, the average lifetime of storm cells was 23.6 min, the average gust wind speed was 16.5 m s−1, the average track length was 21.8 km, and the average movement speed was 16.4 m s−1. The average movement of storm cells varied with months, and the storms moved toward the north, the northeast, and the east. It was also demonstrated that there were 19–35 thunderstorm days each year in North Dakota and that, of these, 9–14 thunderstorm days each year were associated with high speed winds. Severe thunderstorms composed 1.7% of all the thunderstorms in 2002–06. The most intense thunderstorm in North Dakota between 2002 and 2006 was associated with a 5-yr-high wind speed of 31.4 m s−1. It was also found that the longer-lasting storms were the stronger storms.
Abstract
Radar and surface thunderstorm data in North Dakota were investigated to obtain the climatology of thunderstorms in the state. A life cycle analysis for the individual storm cells between 2002 and 2006 was carried out, and it was found that June and July were the peak months, late afternoon to early morning was the peak time for thunderstorms, the average lifetime of storm cells was 23.6 min, the average gust wind speed was 16.5 m s−1, the average track length was 21.8 km, and the average movement speed was 16.4 m s−1. The average movement of storm cells varied with months, and the storms moved toward the north, the northeast, and the east. It was also demonstrated that there were 19–35 thunderstorm days each year in North Dakota and that, of these, 9–14 thunderstorm days each year were associated with high speed winds. Severe thunderstorms composed 1.7% of all the thunderstorms in 2002–06. The most intense thunderstorm in North Dakota between 2002 and 2006 was associated with a 5-yr-high wind speed of 31.4 m s−1. It was also found that the longer-lasting storms were the stronger storms.
Abstract
A number of field experiments and subsequent studies in the 1970s and 1980s have led to the belief that radiative processes play a more significant role in the evolution of tropical mesoscale convective systems (MCSS) than was once thought. In this study, an interactive radiative transfer scheme is incorporated into a two-dimensional version of the Pennsylvania State University-NCAR Mesoscale Model to simulate the evolution of these systems within a large-scale environment under a diurnally varying radiative influence. The radiative effects are examined in terms of the net rainfall, diurnal phasing, and the vertical distribution of diabatic heating within the systems. In addition, three current radiative forcing hypotheses are addressed.
Simulations of individual MCSs with radiation produced more rainfall than those without it. While runs with forced background meant all peaked after the same elapsed time regardless of diurnal initialization time, the peak rainfall rates that occurred at night were greater than those occurring during daytime hours. Without the imposed destabilizing influence of an initialized intertropical convergence zone, rainfall rates peaked near midnight in spite of significantly different model-run start times, and a distinct diurnal cycle was established.
Initialized deep stratiform and cirriform clouds developed mesoscale, edge-oriented convective organization due to the lateral gradients of radiative forcing at the cloud edges. Convective overturning within these mesoscale systems' own trailing anvil clouds was insignificant, and there was no evidence of active latent heating in the clouds great distances away from the convection. A simulation of an MCS with imposed horizontally uniform radiative cooling throughout the domain showed no significant differences in 12-h, domain-averaged rainfall from the control case. Cloud-cloud-free radiative differences tended to modulate the life cycles of the mesoscale circulations within the simulated MCSs, and to concentrate a slightly larger fraction of the total domain rainfall within the MCSs, but they did not significantly alter the MCS structures or net domain rainfall production.
Radiative processes in this study modulate the evolution of tropical mesoscale systems, and hence, tropical rainfall, primarily through large, domainwide destabilization. These simulations indicate that mesoscale radiative forcing through cloud-cloud-free radiative differences and direct destabilization of stratiform clouds is of lesser importance. Although horizontally varying radiative processes appear to play some role in determining the location of convection, they do not appear to have major effects upon either the total amount of or the diurnal variations in tropical rainfall.
Abstract
A number of field experiments and subsequent studies in the 1970s and 1980s have led to the belief that radiative processes play a more significant role in the evolution of tropical mesoscale convective systems (MCSS) than was once thought. In this study, an interactive radiative transfer scheme is incorporated into a two-dimensional version of the Pennsylvania State University-NCAR Mesoscale Model to simulate the evolution of these systems within a large-scale environment under a diurnally varying radiative influence. The radiative effects are examined in terms of the net rainfall, diurnal phasing, and the vertical distribution of diabatic heating within the systems. In addition, three current radiative forcing hypotheses are addressed.
Simulations of individual MCSs with radiation produced more rainfall than those without it. While runs with forced background meant all peaked after the same elapsed time regardless of diurnal initialization time, the peak rainfall rates that occurred at night were greater than those occurring during daytime hours. Without the imposed destabilizing influence of an initialized intertropical convergence zone, rainfall rates peaked near midnight in spite of significantly different model-run start times, and a distinct diurnal cycle was established.
Initialized deep stratiform and cirriform clouds developed mesoscale, edge-oriented convective organization due to the lateral gradients of radiative forcing at the cloud edges. Convective overturning within these mesoscale systems' own trailing anvil clouds was insignificant, and there was no evidence of active latent heating in the clouds great distances away from the convection. A simulation of an MCS with imposed horizontally uniform radiative cooling throughout the domain showed no significant differences in 12-h, domain-averaged rainfall from the control case. Cloud-cloud-free radiative differences tended to modulate the life cycles of the mesoscale circulations within the simulated MCSs, and to concentrate a slightly larger fraction of the total domain rainfall within the MCSs, but they did not significantly alter the MCS structures or net domain rainfall production.
Radiative processes in this study modulate the evolution of tropical mesoscale systems, and hence, tropical rainfall, primarily through large, domainwide destabilization. These simulations indicate that mesoscale radiative forcing through cloud-cloud-free radiative differences and direct destabilization of stratiform clouds is of lesser importance. Although horizontally varying radiative processes appear to play some role in determining the location of convection, they do not appear to have major effects upon either the total amount of or the diurnal variations in tropical rainfall.
Abstract
Forecast probabilities of rain were calculated up to 12 hours in advance using a Markov chain model applied to three-hourly observations from five major Australian cities. The four weather states chosen in this first study were three cloudiness states (0–2 oktas, 3–5 oktas and 6–8 oktas) and a rain state. Second-order Markov models with time-of-day dependent transition probabilities were fitted after appropriate statistical testing.
Forecasts were made using transition probabilities for summer and winter seasons. The skill of the Markov chain forecast probabilities of rain was evaluated in terms of Brier scores using to years of independent data, and compared with forecasts based upon persistence and climatology. The skill of the Markov model forecasts appreciably exceeded that of persistence and climatology and a real time trial of the procedure is being planned.
Abstract
Forecast probabilities of rain were calculated up to 12 hours in advance using a Markov chain model applied to three-hourly observations from five major Australian cities. The four weather states chosen in this first study were three cloudiness states (0–2 oktas, 3–5 oktas and 6–8 oktas) and a rain state. Second-order Markov models with time-of-day dependent transition probabilities were fitted after appropriate statistical testing.
Forecasts were made using transition probabilities for summer and winter seasons. The skill of the Markov chain forecast probabilities of rain was evaluated in terms of Brier scores using to years of independent data, and compared with forecasts based upon persistence and climatology. The skill of the Markov model forecasts appreciably exceeded that of persistence and climatology and a real time trial of the procedure is being planned.
Abstract
Although diabatic processes play an important role in the tropical circulation, current analysis schemes and numerical weather prediction models are unable to adequately include diabatic heating information. In this paper, procedures for using outgoing longwave radiation data as proxy data for diabatic heating rates and to initialize the moisture field are proposed. The feasibility of using this data in the ECMWF data assimilation system is demonstrated, and it is further shown that using appropriate diabatic heating together with moisture initialization has the potential to substantially reduce the spinup time in numerical weather prediction models.
Abstract
Although diabatic processes play an important role in the tropical circulation, current analysis schemes and numerical weather prediction models are unable to adequately include diabatic heating information. In this paper, procedures for using outgoing longwave radiation data as proxy data for diabatic heating rates and to initialize the moisture field are proposed. The feasibility of using this data in the ECMWF data assimilation system is demonstrated, and it is further shown that using appropriate diabatic heating together with moisture initialization has the potential to substantially reduce the spinup time in numerical weather prediction models.
