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Benjamin M. Miller

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.

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David Miller and J. M. Fritsch

Abstract

A climatological study of mesoscale convective complexes (MCCs) during 1983–1985 over the western Pacific region (WPR), using full-disc, enhanced infrared satellite imagery from the Japanese Geostationary Meteorological Satellite is presented.

The results indicate that MCCs are common in the WPR and display many of the same characteristics as those found in the Americas. The systems are nocturnal and tend to form over or in the immediate vicinity of land. Cold-cloud shields in the Americas last for about 10 h while WPR shields last about 11 h. The cold-cloud-shield size distribution is similar to that of the Americas, with most systems exhibiting areas between 2 × 105 and 3 × 105 km2. Seasonal distributions of WPR systems are also similar to that in the Americas. Specifically, the frequency of midlatitude systems peaks in late spring and early summer while low-latitude MCCs are distributed uniformly throughout the warm season.

As with western systems, WPR MCCs occur in preferred zones. Climatologically, low-level jets of high-θe, air and upper-level diffluence are present in these zones. Tracks of WPR MCCs show that, like American systems, they typically move to the right (left in the Southern Hemisphere) of the climatological mean 700–500-mb flow. The deviation from the mean flow is in the direction of the source region of higher-θe air. A few MCCs that moved over water formed tropical storms. Likewise, a few tropical systems moved over land and formed MCCs.

It is concluded that the strong similarity of the properties and environment of WPR MCCs to that in the Americas indicates that they are essentially the same phenomenon. Their high frequency in the Americas and the WPR makes them potentially important contributors to the global hydrologic cycle.

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Kamal Puri and M. J. Miller

Abstract

The sensitivity of the ECMWF analysis-forecast system for four tropical cyclones during the period spanned by the Australian Monsoon Experiment to cumulus parameterization and model resolution is presented. Two parameterization schemes were compared: namely, the Kuo cumulus parameterization and the Betts-Miller adjustment scheme. Both analyses and forecasts show considerable sensitivity with the Betts-Miller scheme generating more intense cyclonic systems as indicated by maps of sea-level pressure, low-level winds, vorticities, and cross sections in the neighborhood of the cyclones. The Betts-Miller scheme also results in better consistency of the fields in the vertical between the divergent circulation and vertical velocity. Of the two cases considered, one (for tropical cyclone Jason) showed a marked sensitivity to increased model resolution with the higher resolution forecast showing considerable improvement.

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Kamal Puri and M. J. Miller

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.

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Faizul M. Mohee and Craig Miller

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.

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A. J. Miller and L. M. Leslie

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.

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Rosemary Auld Miller and William M. Frank

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.

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RAYMOND M. McINTURFF and ALVIN J. MILLER

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).

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Alvin J. Miller and Christopher M. Hayden

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.

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