Among all atmospheric hazards, heat is the most deadly. With such recent notable heat events as the Chicago Heat Wave of 1995, much effort has gone into redeveloping both the methods by which it is determined whether a day will be “oppressive,” as well as the mitigation plans that are implemented when an oppressive day is forecast to occur.

This article describes the techniques that have been implemented in the development of new synoptic-based heat watch–warning systems. These systems are presently running for over two dozen locations worldwide, including Chicago, Illinois; Toronto, Ontario, Canada; Rome, Italy; and Shanghai, China; with plans for continued expansion. Compared to traditional systems based on arbitrary thresholds of one or two meteorological variables, these new systems account for the local human response by focusing upon the identification of the weather conditions most strongly associated with historical increases in mortality. These systems must be constructed based on the premise that weather conditions associated with increased mortality show considerable variability on a spatial scale. In locales with consistently hot summers, weather/mortality relationships are weaker, and it is only the few hottest days each year that are associated with a response. In more temperate climates, relationships are stronger, and a greater percentage of days can be associated with an increase in mortality.

Considering the ease of data transfer via the World-Wide Web, the development of these systems includes Internet file transfers and Web page creation as components. Forecasts of mortality and recommendations to call excessive-heat warnings are available to local meteorological forecasters, local health officials, and other civic authorities, who ultimately determine when warnings are called and when intervention plans are instituted.

Abstract

Two case studies are used to examine the relationship of the sulfate concentration in surface precipitation to the microphysical characteristics of the precipitating cloud systems. The data from one case study support the contention that existing sulfate aerosol was incorporated into cloud water by the nucleation process and accounted for nearly all of the observed cloud and precipitation water sulfate concentration. These activated sulfate particles comprised nearly 60% of the clear-air sulfate mass concentration. Once nucleated, the sulfate particles accumulated water through the condensation process and were subsequently deposited at the surface after accretion on large snowflakes. The presumption of aqueous phase sulfate oxidation of SO₂ was not necessary to account for the observed sulfate concentrations.

The data from the second case study are more limited and difficult to interpret. Nucleation and below cloud washout appeared to be the main contributors to the surface sulfate concentration in precipitation water.

Abstract

A lidar (0.694 μm wavelength) and a passive radiometer (10–12 μm) have been used together to remotely sense the optical properties and gross structure of cirrus (the LIRAD method).

This article reports on observations of midlatitude cirrus taken during two extended experiments at Aspendale, Victoria, Australia, covering one winter season and one summer season and a six-week period of observations of tropical cirrus at Darwin, Northern Territory.

Information has been obtained on the infrared emittance, optical depth, cloud depth, depolarization ratio, “anomalous” backscatter, the effective ratios of backscatter to extinction at the lidar wavelength and the visible to infrared extinction, and the backscatter profile of cirrus.

The results show that the infrared emittance and volume absorption coefficient of midlatitude cirrus, when averaged over a year, are close functions of the midcloud temperature. Very similar relationships hold for tropical cirrus, taking into amount the limited samples. Mean values of beam emittance (10–12 μm) at Aspendale and Darwin were 0.33 and 0. 115, respectively, translating into broadband flux emittance values of 0.52 and 0.30, respectively.

Cirrus cloud depths at Aspendale were quite similar for the winter and summer seasons, varying from 1 to 2 km at −65°C to 2 to 4 km at −35°C, and decreasing again to 1 to 2.5 km at −15°C. The cloud depths at Darwin showed a similar pattern, but the maximum depths of 2 to 3 km occurred between −55° and −70°C, dropping dramatically for both higher and lower temperatures.

Integrated depolarization ratios varied from 0.4 at −60°C to 0.25 at −30°C in the midlatitude cirrus. At higher temperatures, the ratios showed a branching behavior, with some values clustered around a value of 0.38 and others around a value of 0.07. This branching was less evident in summer, with values failing to about 0. 14 at −15°C. The depolarization ratios in tropical cirrus were much less variable, with values ranging from 0.3 at −75°C to 0.27 at −50°C.

A method was developed for separating “normal” and “anomalous” backscatter, the latter being characterized by very intense backscatter coupled with a low depolarization ratio. This allowed a more accurate calculation of optical quantities for normal backscatter and also indicated that anomalous backscatter was present in over 50% of returns at temperatures in the −20° to −30°C range.

The backscatter-to-extinction ratio k/2η showed different characteristics in the summer and winter midlatitude cirrus when plotted against temperature, but these differences disappeared to some extent when k/2η was plotted against altitude. The values of k/2η in tropical cirrus appeared to be rather independent of temperature.

The effects of a variable multiple scattering factor were investigated, and it was found that a variable factor tended to cause the values deduced on the simple theory of a constant η to be too high. Values of the elective ratio of visible extinction to infrared absorption (2αη) deduced for the midlatitude cirrus showed little variation between summer and winter, with values varying from about 2.3 to 1.8 between temperatures of −50° and −20°C. In tropical cirrus, the corresponding values was 3.3.

Average cloud profiles of backscatter indicated large differences between temperatures greater and less than −30°C due to anomalous backscatter in the former case. The profiles also indicated a systematic decrease in backscatter toward cloud base, thought to be due to evaporation of crystals near the base.

Uncertainty in the behavior of η is still the largest stumbling block to the calculation of fundamental quantities such as α and k. The visible optical depth can be calculated to only about 50% accuracy using the lidar backscatter values and derived values of k. A value to about 30% accuracy can be calculated from the infrared volume absorption coefficient σ _A together with theoretical values of α.

Abstract

This work applies a quantitative metric in order to capture the relative representativeness of nonsimultaneous or noncollocated observations and quantify how these observations decorrelate in both space and time. This methodology allows for the effective determination of thresholding decisions for representative matchup conditions and is especially useful for informing future network designs and architectures. Future weather and climate satellite missions must consider a range of architectural trades to meet observing requirements. Frequently, fundamental decisions such as the number of observatories, the instruments manifested, and orbit parameters are determined based upon assumptions about the characteristic temporal and spatial scales of variability of the target observation. With the introduced methodology, representativity errors due to separations in space and time can be quantified without prior knowledge of instrument performance, and errors driven by constellation design can be estimated without model ingest or analysis.

Abstract

Quantitative precipitation estimates have been made for the GARP (Global Atmospheric Research Program) Atlantic Tropical Experiment (GATE) from geosynchronous, infrared satellite imagery and a computer-automated technique that is described in this paper. Volumetric rain estimates were made for the GATE A scale (1.43 × 10⁷ km²) and for a 3° square (1.10 × 10⁵ km²) that enclosed the B scale for time frames ranging from all of GATE (27 June—20 September 1974) down to 6 h segments. The estimates for the square are compared with independent rain measurements made by four C-band digital radars that were complemented by shipboard raingages. The A-scale estimates are compared to rainfall estimates generated by NASA using Nimbus 5 microwave imagery. Other analyses presented include: 1) comparisons of the satellite rain estimates over Africa with raingage measurements, 2) maps of satellite-inferred locations and frequencies of new cumulonimbus cloud formation, mergers and dissipations, 3) latitudinal precipitation cross sections along several longitudes and 4) diurnal rainfall patterns.

The satellite-generated B-scale rainfall patterning is similar to, and the rain volumes are within a factor of 1.10, of those provided by radar for phases 1 and 3. The isohyetal patterns are similar in phase 2, but the satellite estimates are low, relative to the radar, by a factor of 1.73. The B-scale disparity in phase 2 is probably due to the existence of rather shallow but rain-productive convective clouds in the B scale. This disparity apparently does not carry over to the A scale in phase 2. Comparison of NASA Electronically Scanning Microwave Radiometer (ESMR) rain estimates with ours for several areas within the A scale for all GATE suggests that the former is low relative to the latter by a factor of 1.50. The satellite estimates of rainfall in Africa are similar to measurements by raingages in all phases of GATE up to 11°N and progressively greater than the gage measurements north of this latitude toward the Sahara desert.

The diurnal rainfall studies suggest a midday (about 1200 GMT) maximum of rainfall over the water areas and a late evening maximum (about 0000 GMT) over Africa and the northern part of South America. The latitudinal cross sections along several longitudes of phase rainfall clearly show the west-southwest/east-northeast orientation of the Intertropical Convergence Zone (ITCZ), the diminution of the rainfall west-southwestward from Africa into the Atlantic, and the northward progression of the ITCZ from phase 1 into phases 2 and 3. The center of action for cloud formation, merger and dissipation, and the area of maximum rainfall (>1600 mm for all of GATE) occur along the southwest African coast near 11°N. This agrees with past climatologies for this region. Superposition of the satellite-generated rainfall maps and sea surface temperature maps by phase suggests a strong relationship between the two. Almost all of the rainfall occurs within 26°C sea surface temperature envelope. The mean daily coverage of rainfall and the mean rainfall in the raining areas for the A scale for all GATE are 20% and 14.1 mm day⁻¹, respectively. These and other results are discussed.

Abstract

Gaining a better understanding of the influence of clouds on the earth's energy budget requires a cloud classification that takes into account cloud height, thickness, and cloud cover. The radiometer ScaRaB (scanner for radiation balance), which was launched in January 1994, has two narrowband channels (0.5–0.7 and 10.5–12.5 µm) in addition to the two broadband channels (0.2–4 and 0.2–50 µm) necessary for earth radiation budget (ERB) measurements in order to improve cloud detection. Most automatic cloud classifications were developed with measurements of very good spatial resolution (200 m to 5 km). Earth radiation budget experiments (ERBE), on the hand, work at a spatial resolution of about 50 km (at nadir), and therefore a cloud field classification adapted to this scale must be investigated. For this study, ScaRaB measurements are simulated by collocated Advanced Very High Resolution Radiometer (AVHRR) ERBE data. The best-suited variables for a global cloud classification are chosen using as a reference cloud types determined by an operationally working threshold algorithm applied to AVHRR measurements at a reduced spatial resolution of 4 km over the North Atlantic. Cloud field types are then classified by an algorithm based on the dynamic clustering method. More recently, the authors have carried out a global cloud field identification using cloud parameters extracted by the 3I (improved initialization inversion) algorithm, from High-Resolution Infrared Sounder (HIRS)-Microwave Sounding Unit (MSU) data. This enables the authors first to determine mean values of the variables best suited for cloud field classification and then to use a maximum-likelihood method for the classification. The authors find that a classification of cloud fields is still possible at a spatial resolution of ERB measurements. Roughly, one can distinguish three cloud heights and two effective cloud amounts (combination of cloud emissivity and cloud cover). However, only by combining flux measurements (ERBE) with cloud field classifications from sounding instruments (HIRS/MSU) can differences in radiative behavior of specific cloud fields be evaluated accurately.

Abstract

Eight years of cloud properties retrieved from Television Infrared Observation Satellite-N (TIROS-N) Observational Vertical Sounder (TOVS) observations aboard the NOAA polar orbiting satellites are presented. The relatively high spectral resolution of these instruments in the infrared allows especially reliable cirrus identification day and night. This dataset therefore provides complementary information to the International Satellite Cloud Climatology Project (ISCCP). According to this dataset, cirrus clouds cover about 27% of the earth and 45% of the Tropics, whereas ISCCP reports 19% and 25%, respectively. Both global datasets agree within 5% on the amount of single-layer low clouds, at 30%. From 1987 to 1995, global cloud amounts remained stable to within 2%. The seasonal cycle of cloud amount is in general stronger than its diurnal cycle and it is stronger than the one of effective cloud amount, the latter the relevant variable for radiative transfer. Maximum effective low cloud amount over ocean occurs in winter in SH subtropics in the early morning hours and in NH midlatitudes without diurnal cycle. Over land in winter the maximum is in the early afternoon, accompanied in the midlatitudes by thin cirrus. Over tropical land and in the other regions in summer, the maximum of mesoscale high opaque clouds occurs in the evening. Cirrus also increases during the afternoon and persists during night and early morning. The maximum of thin cirrus is in the early afternoon, then decreases slowly while cirrus and high opaque clouds increase. TOVS extends information of ISCCP during night, indicating that high cloudiness, increasing during the afternoon, persists longer during night in the Tropics and subtropics than in midlatitudes. A comparison of seasonal and diurnal cycle of high cloud amount between South America, Africa, and Indonesia during boreal winter has shown strong similarities between the two land regions, whereas the Indonesian islands show a seasonal and diurnal behavior strongly influenced by the surrounding ocean. Deeper precipitation systems over Africa than over South America do not seem to be directly reflected in the horizontal coverage and mesoscale effective emissivity of high clouds.

Abstract

The Geostationary Operational Environmental Satellite-14 (GOES-14) imager was operated by the National Oceanic and Atmospheric Administration (NOAA) in an experimental rapid scan 1-min mode during parts of the summers of 2012 and 2013. This scan mode, known as the super rapid scan operations for GOES-R (SRSOR), emulates the high-temporal-resolution sampling of the mesoscale region scanning of the Advanced Baseline Imager (ABI) on the next-generation GOES-R series. This paper both introduces these unique datasets and highlights future satellite imager capabilities. Many phenomena were observed from GOES-14, including fog, clouds, severe storms, fires and smoke (including the California Rim Fire), and several tropical cyclones. In 2012 over 6 days of SRSOR data of Hurricane Sandy were acquired. In 2013, the first two days of SRSOR in June observed the propagation and evolution of a mid-Atlantic derecho. The data from August 2013 were unique in that the GOES imager operated in nearly continuous 1-min mode; prior to this time, the 1-min data were interrupted every 3 h for full disk scans. Used in a number of NOAA test beds and operational centers, including NOAA’s Storm Prediction Center (SPC), the Aviation Weather Center (AWC), the Ocean Prediction Center (OPC), and the National Hurricane Center (NHC), these experimental data prepare users for the next-generation imager, which will be able to routinely acquire mesoscale (1,000 km × 1,000 km) images every 30 s (or two separate locations every minute). Several animations are included, showcasing the rapid change of the many phenomena observed during SRSOR from the GOES-14 imager.

Abstract

The climate of high midlatitude mountains appears to be warming faster than the global average, but evidence for such elevation-dependent warming (EDW) at higher latitudes is presently scarce. Here, we use a comprehensive network of remote meteorological stations, proximal radiosonde measurements, downscaled temperature reanalysis, ice cores, and climate indices to investigate the manifestation and possible drivers of EDW in the St. Elias Mountains in subarctic Yukon, Canada. Linear trend analysis of comprehensively validated annual downscaled North American Regional Reanalysis (NARR) gridded surface air temperatures for the years 1979–2016 indicates a warming rate of 0.028°C a⁻¹ between 5500 and 6000 m above mean sea level (MSL), which is ~1.6 times larger than the global-average warming rate between 1970 and 2015. The warming rate between 5500 and 6000 m MSL was ~1.5 times greater than the rate at the 2000–2500 m MSL bin (0.019°C a⁻¹), which is similar to the majority of warming rates estimated worldwide over similar elevation gradients. Accelerated warming since 1979, measured by radiosondes, indicates a maximum rate at 400 hPa (~7010 m MSL). EDW in the St. Elias region therefore appears to be driven by recent warming of the free troposphere. MODIS satellite data show no evidence for an enhanced snow albedo feedback above 2500 m MSL, and declining trends in sulfate aerosols deposited in high-elevation ice cores suggest a modest increase in radiative forcing at these elevations. In contrast, increasing trends in water vapor mixing ratio at the 500-hPa level measured by radiosonde suggest that a longwave radiation vapor feedback is contributing to EDW.

Abstract

Since 2007, meteorologists of the U.S. Army Test and Evaluation Command (ATEC) at Dugway Proving Ground (DPG), Utah, have relied on a mesoscale ensemble prediction system (EPS) known as the Ensemble Four-Dimensional Weather System (E-4DWX). This article describes E-4DWX and the innovative way in which it is calibrated, how it performs, why it was developed, and how meteorologists at DPG use it. E-4DWX has 30 operational members, each configured to produce forecasts of 48 h every 6 h on a 272-processor high performance computer (HPC) at DPG. The ensemble’s members differ from one another in initial-, lateral-, and lower-boundary conditions; in methods of data assimilation; and in physical parameterizations. The predictive core of all members is the Advanced Research core of the Weather Research and Forecasting (WRF) Model. Numerical predictions of the most useful near-surface variables are dynamically calibrated through algorithms that combine logistic regression and quantile regression, generating statistically realistic probabilistic depictions of the atmosphere’s future state at DPG’s observing sites. Army meteorologists view E-4DWX’s output via customized figures posted to a restricted website. Some of these figures summarize collective results—for example, through means, standard deviations, or fractions of the ensemble exceeding thresholds. Other figures show each forecast, individually or grouped—for example, through spaghetti diagrams and time series. This article presents examples of each type of figure.