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Radar is an important tool for investigating and forecasting processes in Earth’s atmosphere. More specifically, multiple frequencies of radar with sensitivities to cloud and precipitation regimes are important for process-level weather and climate studies. An online educational applet (http://lecuyer.aos.wisc.edu/radarlabviewer) has been developed to provide a learning experience about this topic with an intended audience of undergraduate and graduate university–level students. Cloud-resolving model data coupled with a radar instrument simulator provide a three-dimensional view of a midlatitude winter cyclone that is explorable through the applet. This synthetic laboratory environment provides direct comparisons between modeled hydrometeors and simulated instrument observations allowing students to visualize the concepts of attenuation, non-Rayleigh scattering, insensitivity of instruments, and viewing perspective. Variations in the minimum detectable signal of instruments also expose students to the real-world tradeoffs between instrument features and costs. Additional development and formal educational assessment of the applet is planned in the future.

Continental mosaics of radar data have now been generated for more than 20 years. They offer information on precipitation climatology that is simply not available or archived elsewhere: How often does it rain at any particular location? At what time? And with what intensity distribution? What are the geographical and temporal patterns of precipitation occurrence, formation, and decay? What is the climatology of severe weather? Answers to these questions have value on their own and invariably trigger more questions about the processes causing these patterns but also suggest some answers. They also have considerable pedagogical value in illustrating in the classroom the impacts of different processes—such as sea–land breezes, topography, and seasons—on precipitation. In this work, U.S. mosaics of radar data from 1996 to 2015 are used to demonstrate the possibilities offered by such a dataset. Three topics are discussed: (i) climatologies and daily cycles of precipitation and convection, and what they can teach us about precipitation mechanisms; (ii) the spatial and temporal distribution of the appearance and occurrence of convection, and what it reveals about the importance of surface terrain properties for these events; and (iii) the power and challenges of looking for a small signal in such a large dataset using the influence of weekly activity cycles and cities on precipitation as an illustration.

The growth of the wind industry in recent years has motivated investigation into wind farm interference with the operation of the nationwide Weather Surveillance Radar-1988 Doppler (WSR-88D) network. Observations of a wind farm were taken with a Doppler on Wheels (DOW) during the DOW Radar Observations at Purdue Study (DROPS), a largely studentled field program that took place in the fall of 2009. The DOW sampled clear-air weather and precipitation at locations within 5 km of the Benton County, Indiana, wind farm to determine the wind turbines' effect on Doppler velocity and ref lectivity data. These data were analyzed and compared with data from the Indianapolis WSR-88D (KIND) and a local television station (WLFI) radar. In precipitation, the DOW data show velocity couplets that have the appearance of isolated tornadic vortices. Under clear-air sampling, significant multipath scattering is evident, but no velocity couplets would meet the DOW-equivalent tornado detection algorithm criteria. Broader impacts of these findings are discussed, and suggestions are made for additional studies that would explore how to mitigate these impacts.

The NSF Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere (CASA) is advancing a new approach to radar network design based on dense networks of short-range radars. The center's concept is to deploy small radars atop communication towers, rooftops, and other elements of the infrastructure as a means to comprehensively map winds, rainfall, and other atmospheric and airborne objects throughout the atmosphere with resolution, low-altitude coverage, Doppler wind vector measurement, and other capabilities that are substantially beyond the current state-of-the-art. The technology has the potential to supplement - or perhaps replace - the large long-range civil infrastructure radars in use today.

Dual-polarization weather radars have evolved significantly in the last three decades culminating in operational deployment by the National Weather Service. In addition to operational applications in the weather service, dual-polarization radars have shown significant potential in contributing to the research fields of ground-based remote sensing of rainfall microphysics, the study of precipitation evolution, and hydrometeor classification. Microphysical characterization of precipitation and quantitative precipitation estimation are important applications that are critical in the validation of satellite-borne precipitation measurements and also serve as valuable tools in algorithm development. This paper presents the important role played by dual-polarization radar in validating spaceborne precipitation measurements. Examples of raindrop size distribution retrievals and hydrometeor-type classification are discussed. The quantitative precipitation estimation is a product of direct relevance to spaceborne o...

During the past 20 yr there has been substantial progress on the development and application of millimeter-wavelength (3.2 and 8.6 mm, corresponding to frequencies of 94 and 35 GHz) radars in atmospheric cloud research, boosted by continuous advancements in radar technology and the need to better understand clouds and their role in the Earth's climate. Applications of millimeter-wavelength radars range from detailed cloud and precipitation process studies to long-term monitoring activities that strive to improve our understanding of cloud processes over a wide range of spatial and temporal scales. These activities are the result of a long period of successful research, starting from the 1980s, in which research tools and sophisticated retrieval techniques were developed, tested, and evaluated in field experiments. This paper presents a cohesive, chronological overview of millimeter-wavelength radar advancements during this period and describes the potential of new applications of millimeter-wavelength rad...

In final form 30 May 2007 © 2007 American Meteorological Society he global hydrological cycle is central to Earth’s climate system, with rainfall and the physics of precipitation formation acting as the key links in the cycle. Two-thirds of global rainfall occurs in the Tropics with the associated latent heat (LH) release accounting for three-fourths of the total heat energy available to Earth’s atmosphere. In addition, freshwater provided by tropical rainfall and its variability exerts a large impact upon the structure and motion of the upper-ocean layer. The four-dimensional distribution of precipitation in the tropical atmosphere has been observed by the Tropical Rainfall Measuring Mission (TRMM) satellite since its launch in November 1997. TRMM’s passive microwave radiometer [TRMM Microwave Imager (TMI)] and precipitation radar (PR) are the primary instruments providing these data. In the last decade, standard LH products from TRMM measurements have become valuable resources for scientific research and applications. Such products enable new insights on and investigations of the complexities of convective life cycles, the diabatic heating controls and feedbacks of mesosynoptic circulations and their forecasts, the relationship of patterns of tropical LH to the global circulation and climate, and strategies for improving cloud parameterizations in environmental prediction models. The Fourth TRMM Latent Heating Workshop was convened to exchange scientific information and experience concerning the retrieval, validation, and application of satellite-derived LH products. In addition, the 26 participants met to examine and discuss the results of a comprehensive LH algorithm intercomparison–validation project; define an initial set of standard LH products; discuss validation issues, particularly the use of diagnostic analysis as the primary validation approach; deliberate further scientific requirements and applications issues related to standardized TRMM LH products; and identify future data products and validation procedures that will be required for the upcoming Global Precipitation Measurement (GPM) Mission. THE FOURTH TRMM LATENT HEATING WORKSHOP

A group of scientists from three universities across two different states and from one federal research laboratory joined together to build and deploy two mobile C-band Doppler weather radars to enhance research and promote meteorological education. This 5-yr project led to the development of the Shared Mobile Atmospheric Research and Teaching (SMART) radar coalition that built the first mobile C-band Doppler weather radar in the United States and also successfully deployed the first mobile C-band dual-Doppler network in a landfalling hurricane. This accomplishment marked the beginning of an era in which high temporal and spatial resolution precipitation and dual-Doppler wind data over mesoscale (∼100 km) regions can be acquired from mobile ground-based platforms during extreme heavy rain and high-wind events. In this paper, we discuss the rationale for building the mobile observing systems, highlight some of the challenges that were encountered in creating a unique multia-gency coalition, provid...

During May–July 2000, the Severe Thunderstorm Electrification and Precipitation Study (STEPS) occurred in the High Plains, near the Colorado–Kansas border. STEPS aimed to achieve a better understanding of the interactions between kinematics, precipitation, and electrification in severe thunderstorms. Specific scientific objectives included 1) understanding the apparent major differences in precipitation output from super-cells that have led to them being classified as low precipitation (LP), classic or medium precipitation, and high precipitation; 2) understanding lightning formation and behavior in storms, and how lightning differs among storm types, particularly to better understand the mechanisms by which storms produce predominantly positive cloud-to-ground (CG) lightning; and 3) verifying and improving microphysical interpretations from polarimetric radar. The project involved the use of a multiple-Doppler polarimetric radar network, as well as a time-of-arrival very high frequency (VHF) lig...

A method for determining horizontal wind speeds in hurricanes using ground-based radars is presented and evaluated. The method makes use of the tracking reflectivity echos by correlation (TREC) method where individual features in radar reflectivity are tracked, from radar sweeps several minutes apart, by finding the maxima in the cross-correlation function between the two times. This method has been applied successfully in determining motions within the clear boundary layer where reflectors are insects and refractive index variations, but it generally has failed when applied to determining air motions by tracking precipitation elements in strong environmental shear. It appears to work in the lower few kilometers of the hurricane where the vertical wind shear is relatively weak. Examples are presented where the TREC algorithm is applied to three landfalling hurricanes: Hurricanes Hugo and Erin in the United States and Typhoon Herb in Taiwan. The results from Hugo, where the radar data were provided by a WS...

It was once generally thought that stratiform precipitation was something occurring primarily, if not exclusively, in middle latitudes—in baroclinic cyclones and fronts. Early radar observations in the Tropics, however, showed large radar echoes composed of convective rain alongside stratiform precipitation, with the stratiform echoes covering great areas and accounting for a large portion of the tropical rainfall. These observations seemed paradoxical, since stratiform precipitation should not have been occurring in the Tropics, where baroclinic cyclones do not occur. Instead it was falling from convection-generated clouds, generally thought to be too violent to be compatible with the layered, gently settling behavior of stratiform precipitation. In meteorology, convection is a dynamic concept; specifically, it is the rapid, efficient, vigorous overturning of the atmosphere required to neutralize an unstable vertical distribution of moist static energy. Most clouds in the Tropics are convection-generated...

A brief description is given of NOAA's 404-MHz Wind Profiler Demonstration Network (WPDN), including the radar configuration, sampling strategy, site locations and characteristics, and a discussion of the Doppler power spectrum and its first three spectral moments: signal power (S), radial velocity (Vr), and velocity variance (σ2). Evidence is presented showing that 6-min time resolution spectral moment data from the vertically pointing beam of a WPDN wind profiler can be used to identify when precipitation is present above the profiler. Signatures of snow, light and moderate stratiform rain, heavy convective rain, freezing rain, and snow within jet stream cirrus are illustrated and summarized. Although radar reflectivity factor (Z) cannot be determined from WPDN wind profilers, the precipitation rates and fall speeds shown to be observable in the cases documented here are roughly consistent with earlier studies suggesting that precipitation with Z > 0–15 dBZ should typically be observable at 404 MHz, and...

The Global Precipitation Climatology Project (GPCP) was established by the World Climate Research Program to produce global analyses of the area- and time-averaged precipitation for use in climate research. To achieve the required spatial coverage, the GPCP uses simple rainfall estimates derived from IR and microwave satellite observations. In this paper, we describe the GPCP and its first Algorithm Intercomparison Project (AIP/1), which compared a variety of rainfall estimates derived from Geostationary Meteorological Satellite visible and IR observations and Special Sensor Microwave/Imager (SSM/I) microwave observations with rainfall derived from a combination of radar and raingage data over the Japanese islands and the adjacent ocean regions during the June and mid-July through mid-August periods of 1989. To investigate potential improvements in the use of satellite IR data for the estimation of large-scale rainfall for the GPCP, the relationship between rainfall and the fractional coverage of cold clouds in the AIP/1 dataset is examined. Linear regressions between fractional coverage and rainfall are analyzed for a number of latitude-longitude areas and for a range of averaging times. The results show distinct differences in the character of the relationship for different portions of the area. These results suggest that the simple IR-based estimation technique currently used in the GPCP can be used to estimate rainfall for global tropical and subtropical areas, provided that a method for adjusting the proportional coefficient for varying areas and seasons can be determined.

Radar can produce detailed precipitation information for large areas from a single location in real time. Although radar has been used experimentally for nearly 30 years to measure rainfall, operational implementation has been slow. Today we find that data are underutilized and both confusion and misunderstanding exist about the inherent ability of radar to measure rainfall, about factors that contribute to errors, and about the importance of careful calibration and signal processing. Areal and point rainfall estimates are often in error by a factor of two or more. Error sources reside in measurement of radar reflectivity factor, evaporation and advection of precipitation before reaching the ground, and variations in the drop-size distribution and vertical air motions. Nevertheless, radar can be of lifesaving usefulness by alerting forecasters to the potential for flash flooding. The most successful technique for improving the radar rainfall estimates has been to “calibrate” the radar with rain g...

The proposed Tropical Rainfall Measuring Mission (TRMM) satellite (presently in its third year of planning), is described. The TRMM satellite, planned for an operational duration of at least three years beginning in the mid-1990s, is intended to obtain high-quality measurements of tropical precipitation by means of information derived from a quantitative spaceborne radar, a multichannel passive microwave radiometer, and an AVHRR. The satellite's orbit will be low-altitude (320 km), for high resolution, and low-inclination (30 to 35 deg), for making it possible to visit each sampling area twice a day. Radar and passive microwave algorithms and rain-retrieval algorithms to be used in precipitation measurements are discussed together with cloud dynamical models designed to test these algorithms.

Data collected in Illinois on the behavior of growing cumulus clouds and their associated radar echoes are reviewed and the results are compared to findings in other regions. It is shown that the data collection techniques used, involving two panoramic cameras and a RHI-type radar, were not too successful in Illinois because of the high cloud density on days of cumulus activity.

Radar data are used to investigate wintertime cold-front precipitation patterns in the vicinity of Cambridge, Massachusetts. No significant correlation was found to exist between the extent of precipitation as indicated by radar-scope coverage and selected synoptic parameters—with the exception of the Instability Index which proved to be significant at the 5 per cent level. Further comparison is made between the average precipitation amounts as indicated by the climatological network of rain gauges and the same synoptic parameters. Again, a significant correlation was found to exist only for the Instability Index.

Appropriate uses of radar in a national weather system within the next 10–15 years are considered. A radar network sensing precipitation reflectivity and utilizing many automatic techniques for acquiring and processing data, preparing forecasts, and communicating precipitation characteristics represents a worthwhile goal practically achievable by 1980. A suitable system would combine the information provided by radar and other sensors, would provide users with the specialized information they require at reasonable cost, and would promote effective interpersonal and man-machine relationships. It would also readily admit new instruments and techniques as their worth is demonstrated. The meteorological applications of reflectivity data are listed and radar data flow rates corresponding to low, moderate, and high load configurations in the envisioned system are presented. Increasing flow rates correspond to increasing proportions of automatic as opposed to manual operations in the system. The system ...

The size, shape and character of radar echoes caused by precipitation as viewed on PPI scopes are related to the clouds in which the precipitation develops. Photographs of PPI scopes showing precipitation echoes of various types are shown together with areal photographs of the clouds in the immediate vicinity of the precipitation. Such a presentation is an aid in the interpretation of radar precipitation echoes.

On the basis of a review of the abstracts of articles published in the last 5 years or so a summary has been prepared of Soviet research activity in the field of radar meteorology. A wide spectrum of topics has been getting some study, but in recent years, Soviet scientists have been giving particular attention to the following areas of research: calculations of the scattering and attenuation cross sections of various hydrometeors; the use of Doppler radar to study the turbulent properties of the atmosphere; the development of procedures by which the characteristics of radar echoes can be used to identify cloud and hydrometeor types, with particular emphasis on the discrimination of severe thunderstorms from other precipitating cloud systems; the detection and measurement of hail; and the measurement of precipitation.

The development of frontal precipitation as observed by radar is illustrated by data taken on a particular storm. This storm presents a typical sequence of precipitation patterns found to be associated with a warm front and a following cold front.

METROMEX, a field project designed and now in progress at St. Louis, involves 4 research groups planning and working cooperatively to study inadvertent weather modification by urban-industrial effects, and, in particular, man-made changes of precipitation. Urban areas affect most forms of weather and some, such as winds, temperature, and visibility, are obvious and their changes are easily measured. inadvertent precipitation changes are harder to measure, and except for the well-documented La Porte anomaly, urban-related rain changes have had only limited study. Examination of historical data at St. Louis has revealed summer increases in the immediate downwind area of. 1) rainfall (10–17%); 2) moderate rain days (11–23%); 3) heavy rainstorms (80%) 4) thunderstorms (21%); and 5) hailstorms (30%). METROMEX field measurements in the summer of 1971 involved 220 raingages and hailpads, 3 radar sets, 70 rainwater collectors, 14 pibal stations, 4 meteorological aircraft, unique atmospheric tracers, and ...

Observations of a sharp cold front and closely associated squall line in New England are analyzed. A striking feature is a line of convective clouds and heavy precipitation, which does not extend above 10,000 ft. The radar indication of the true plan-position and vertical extent of such disturbances is of special importance to air operations.

Are the outer precipitation bands of hurricanes and typhoons important phenomena? In suggesting that the answer to this question is “yes” several features of these bands are described or postulated. Methods of estimating the severity of attendant weather conditions by radar observation are offered.