Search Results

You are looking at 21 - 30 of 32 items for

  • Author or Editor: Brooks E. Martner x
  • Refine by Access: All Content x
Clear All Modify Search
Brooks E. Martner, Robert M. Rauber, Roy M. Rasmussen, Erwin T. Prater, and Mohan K. Ramamurthy

A winter storm that crossed the continental United States in mid-February 1990 produced hazardous weather across a vast area of the nation. A wide range of severe weather was reported, including heavy snowfall; freezing rain and drizzle; thunderstorms with destructive winds, lightning, large hail, and tornadoes; prolonged heavy rain with subsequent flooding; frost damage to citrus orchards; and sustained destructive winds not associated with thunderstorms. Low-end preliminary estimates of impacts included 9 deaths, 27 injuries, and $120 million of property damage. At least 35 states and southeastern Canada were adversely affected. The storm occurred during the field operations of four independent atmospheric research projects that obtained special, detailed observations of it from the Rocky Mountains to the eastern Great Lakes.

Full access
Allen B. White, James R. Jordan, Brooks E. Martner, F. Martin Ralph, and Bruce W. Bartram

Abstract

A new S-band vertical profiler with a coupler option for extending the dynamic range of the radar’s receiver is discussed. The added dynamic range allows the profiler to record radar reflectivity measurements in moderate to heavy precipitation that otherwise would not have been possible with this system because of receiver saturation. The radar hardware, signal processor, and operating software are based on existing S-band and UHF profiler technology. Results from a side-by-side comparison with a calibrated Ka-band radar are used to determine the calibration and sensitivity of the S-band profiler. In a typical cloud profiling mode of operation, the sensitivity is −14 dBZ at 10 km. Examples taken from a recent field campaign are shown to illustrate the profiler’s ability to measure vertical velocity and radar reflectivity profiles in clouds and precipitation, with particular emphasis on the benefit provided by the coupler technology.

Full access
Sergey Y. Matrosov, Kurt A. Clark, Brooks E. Martner, and Ali Tokay

Abstract

A combined polarimetric estimator for rainfall rate (R) retrievals from polarimetric radar measurements at X band is proposed. This estimator uses the horizontal polarization radar reflectivity Z e, differential reflectivity Z DR, and specific differential phase shift K DP, and it intrinsically accounts for changes in how drop oblateness increases with size. Because this estimator uses power measurements (i.e., Z e and Z DR), a procedure for correcting these measurements for effects of partial attenuation and differential attenuation using the differential phase measurement is suggested. An altitude correction for estimates of rainfall rates is also suggested. The proposed combined polarimetric estimator that uses K DP, Z DR, and Z e, an estimator that uses K DP alone for equilibrium drop shapes, and different Z eR relations were applied to the 15 rain events observed with the NOAA X-band transportable polarimetric radar during the eight-week field campaign at the NASA Wallops Island facility in Virginia. The observed rains ranged from very light stratiform events to very heavy convective ones with cells producing rainfall rates in excess of 100 mm h−1. The three different ground validation sites were equipped with high-resolution (0.01 in.) tipping-bucket rain gauges. One of these sites also was equipped with disdrometers. In terms of the relative standard deviation, the combined polarimetric estimator provided the best overall agreement with gauge data (22%), closely followed by a case-tuned Z eR relation (23%) that was determined for each observational case from drop size distributions (DSD) measured in situ by a disdrometer and was available only a posteriori. The use of the K DP-only estimator and a mean Z eR relation resulted in 30% and 32% relative standard deviations, correspondingly. The combined polarimetric estimator, the K DP-only estimator, and the case-tuned Z eR relation estimator provided about a 6%–9% negative bias in comparison with the gauge data; the mean Z eR relation estimator provided a larger negative bias (18%).

Full access
Brooks E. Martner, Sandra E. Yuter, Allen B. White, Sergey Y. Matrosov, David E. Kingsmill, and F. Martin Ralph

Abstract

Recent studies using vertically pointing S-band profiling radars showed that coastal winter storms in California and Oregon frequently do not display a melting-layer radar bright band and inferred that these nonbrightband (NBB) periods are characterized by raindrop size spectra that differ markedly from those of brightband (BB) periods. Two coastal sites in northern California were revisited in the winter of 2003/04 in this study, which extends the earlier work by augmenting the profiling radar observations with collocated raindrop disdrometers to measure drop size distributions (DSD) at the surface. The disdrometer observations are analyzed for more than 320 h of nonconvective rainfall. The new measurements confirm the earlier inferences that NBB rainfall periods are characterized by greater concentrations of small drops and smaller concentrations of large drops than BB periods. Compared with their BB counterparts, NBB periods had mean values that were 40% smaller for mean-volume diameter, 32% smaller for rain intensity, 87% larger for total drop concentration, and 81% larger (steeper) for slope of the exponential DSDs. The differences are statistically significant. Liquid water contents differ very little, however, for the two rain types. Disdrometer-based relations between radar reflectivity (Z) and rainfall intensity (R) at the site in the Coast Range Mountains were Z = 168R 1.58 for BB periods and Z = 44R 1.91 for NBB. The much lower coefficient, which is characteristic of NBB rainfall, is poorly represented by the ZR equations most commonly applied to data from the operational network of Weather Surveillance Radar-1988 Doppler (WSR-88D) units, which underestimate rain accumulations by a factor of 2 or more when applied to nonconvective NBB situations. Based on the observed DSDs, it is also concluded that polarimetric scanning radars may have some limited ability to distinguish between regions of BB and NBB rainfall using differential reflectivity. However, differential-phase estimations of rain intensity are not useful for NBB rain, because the drops are too small and nearly spherical. On average, the profiler-measured echo tops were 3.2 km lower in NBB periods than during BB periods, and they extended only about 1 km above the 0°C altitude. The findings are consistent with the concept that precipitation processes during BB periods are dominated by ice processes in deep cloud layers associated with synoptic-scale forcing, whereas the more restrained growth of hydrometeors in NBB periods is primarily the result of orographically forced condensation and coalescence processes in much shallower clouds.

Full access
Paul J. Neiman, Gary A. Wick, F. Martin Ralph, Brooks E. Martner, Allen B. White, and David E. Kingsmill

Abstract

An objective algorithm presented in White et al. was applied to vertically pointing S-band (S-PROF) radar data recorded at four sites in northern California and western Oregon during four winters to assess the geographic, interannual, and synoptic variability of stratiform nonbrightband (NBB) rain in landfalling winter storms. NBB rain typically fell in a shallow layer residing beneath the melting level (<∼3.5 km MSL), whereas rainfall possessing a brightband (BB) was usually associated with deeper echoes (>∼6 km MSL). The shallow NBB echo tops often resided beneath the coverage of the operational Weather Surveillance Radar-1988 Doppler (WSR-88D) scanning radars yet were still capable of producing flooding rains.

NBB rain contributed significantly to the total winter-season rainfall at each of the four geographically distinct sites (i.e., 18%–35% of the winter-season rain totals). In addition, the rainfall observed at the coastal mountain site near Cazadero, California (CZD), during each of four winters was composed of a significant percentage of NBB rain (18%–50%); substantial NBB rainfall occurred regardless of the phase of the El Niño–Southern Oscillation (which ranged from strong El Niño to moderate La Niña conditions). Clearly, NBB rain occurs more widely and commonly in California and Oregon than can be inferred from the single-winter, single-site study of White et al.

Composite NCEP–NCAR reanalysis maps and Geostationary Operational Environment Satellite (GOES) cloud-top temperature data were examined to evaluate the synoptic conditions that characterize periods of NBB precipitation observed at CZD and how they differ from periods with bright bands. The composites indicate that both rain types were tied generally to landfalling polar-cold-frontal systems. However, synoptic conditions favoring BB rain exhibited notable distinctions from those characterizing NBB periods. This included key differences in the position of the composite 300-mb jet stream and underlying cold front with respect to CZD, as well as notable differences in the intensity of the 500-mb shortwave trough offshore of CZD. The suite of BB composites exhibited dynamically consistent synoptic-scale characteristics that yielded stronger and deeper ascent over CZD than for the typically shallower NBB rain, consistent with the GOES satellite composites that showed 20-K warmer (2.3-km shallower) cloud tops for NBB rain. Composite soundings for both rain types possessed low-level potential instability, but the NBB sounding was warmer and moister with stronger low-level upslope flow, thus implying that orographically forced rainfall is enhanced during NBB conditions.

Full access
Brooks E. Martner, Jack B. Snider, Robert J. Zamora, Gregory P. Byrd, Thomas A. Niziol, and Paul I. Joe

Abstract

A destructive freezing-rain storm on 15 February 1990 was observed intensively with advanced ground-based remote sensors and conventional instruments by the Lake Ontario Winter Storms (LOWS) project in upstate New York. A deep layer of warm, moist, southwesterly flow overran a shallower layer of subfreezing, easterly flow ahead of a surface warm front. Precipitation at the surface changed from snowfall to ice pellets, to freezing rain, and, finally, to ordinary rain as an elevated layer of above-freezing air moved into the region and eventually extended to the ground. Measurements from a scanning Doppler radar, wind profilers, a microwave radiometer, and mobile rawinsondes provided detailed information on the storm's kinematic and thermodynamic structure and evolution, and allowed its basic microphysical structure to be inferred. The remote sensors detected signatures of the melting aloft that may be useful for improving detection and forecasts of freezing-rain hazards.

Full access
Sergey Y. Matrosov, Robert Cifelli, Patrick C. Kennedy, Steven W. Nesbitt, Steven A. Rutledge, V. N. Bringi, and Brooks E. Martner

Abstract

A comparative study of the use of X- and S-band polarimetric radars for rainfall parameter retrievals is presented. The main advantage of X-band polarimetric measurements is the availability of reliable specific differential phase shift estimates, K DP, for lighter rainfalls when phase measurements at the S band are too noisy to produce usable K DP. Theoretical modeling with experimental raindrop size distributions indicates that due to some non-Rayleigh resonant effects, K DP values at a 3.2-cm wavelength (X band) are on average a factor of 3.7 greater than at 11 cm (S band), which is a somewhat larger difference than simple frequency scaling predicts. The non-Rayleigh effects also cause X-band horizontal polarization reflectivity, Z eh, and differential reflectivity, Z DR, to be larger than those at the S band. The differences between X- and S-band reflectivities can exceed measurement uncertainties for Z eh starting approximately at Z eh > 40 dBZ, and for Z DR when the mass-weighted drop diameter, Dm, exceeds about 2 mm. Simultaneous X- and S-band radar measurements of rainfall showed that consistent K DP estimates exceeding about 0.1° km−1 began to be possible at reflectivities greater than ∼26–30 dBZ while at the S band such estimates can generally be made if Z eh > ∼35–39 dBZ. Experimental radar data taken in light-to-moderate stratiform rainfalls with rain rates R in an interval from 2.5 to 15 mm h−1 showed availability of the K DP-based estimates of R for most of the data points at the X band while at the S band such estimates were available only for R greater than about 8–10 mm h−1. After correcting X-band differential reflectivity measurements for differential attenuation, Z DR measurements at both radar frequency bands were in good agreement with each other for Dm < 2 mm, which approximately corresponds to Z DR ≈ 1.6 dB. The Z DR-based retrievals of characteristic raindrop sizes also agreed well with in situ disdrometer measurements.

Full access
Kenneth P. Moran, Brooks E. Martner, M. J. Post, Robert A. Kropfli, David C. Welsh, and Kevin B. Widener

A new millimeter-wave cloud radar (MMCR) has been designed to provide detailed, long-term observations of nonprecipitating and weakly precipitating clouds at Cloud and Radiation Testbed (CART) sites of the Department of Energy's Atmospheric Radiation Measurement (ARM) program. Scientific requirements included excellent sensitivity and vertical resolution to detect weak and thin multiple layers of ice and liquid water clouds over the sites and long-term, unattended operations in remote locales. In response to these requirements, the innovative radar design features a vertically pointing, single-polarization, Doppler system operating at 35 GHz (Ka band). It uses a low-peak-power transmitter for long-term reliability and high-gain antenna and pulse-compressed waveforms to maximize sensitivity and resolution. The radar uses the same kind of signal processor as that used in commercial wind profilers. The first MMCR began operations at the CART in northern Oklahoma in late 1996 and has operated continuously there for thousands of hours. It routinely provides remarkably detailed images of the ever-changing cloud structure and kinematics over this densely instrumented site. Examples of the data are presented. The radar measurements will greatly improve quantitative documentation of cloud conditions over the CART sites and will bolster ARM research to understand how clouds impact climate through their effects on radiative transfer. Millimeter-wave radars such as the MMCR also have potential applications in the fields of aviation weather, weather modification, and basic cloud physics research.

Full access
Eugene E. Clothiaux, Thomas P. Ackerman, Gerald G. Mace, Kenneth P. Moran, Roger T. Marchand, Mark A. Miller, and Brooks E. Martner

Abstract

The U.S. Department of Energy’s Atmospheric Radiation Measurement (ARM) Program is deploying sensitive, millimeter-wave cloud radars at its Cloud and Radiation Test Bed (CART) sites in Oklahoma, Alaska, and the tropical western Pacific Ocean. The radars complement optical devices, including a Belfort or Vaisala laser ceilometer and a micropulse lidar, in providing a comprehensive source of information on the vertical distribution of hydrometeors overhead at the sites. An algorithm is described that combines data from these active remote sensors to produce an objective determination of hydrometeor height distributions and estimates of their radar reflectivities, vertical velocities, and Doppler spectral widths, which are optimized for accuracy. These data provide fundamental information for retrieving cloud microphysical properties and assessing the radiative effects of clouds on climate. The algorithm is applied to nine months of data from the CART site in Oklahoma for initial evaluation. Much of the algorithm’s calculations deal with merging and optimizing data from the radar’s four sequential operating modes, which have differing advantages and limitations, including problems resulting from range sidelobes, range aliasing, and coherent averaging. Two of the modes use advanced phase-coded pulse compression techniques to yield approximately 10 and 15 dB more sensitivity than is available from the two conventional pulse modes. Comparison of cloud-base heights from the Belfort ceilometer and the micropulse lidar confirms small biases found in earlier studies, but recent information about the ceilometer brings the agreement to within 20–30 m. Merged data of the radar’s modes were found to miss approximately 5.9% of the clouds detected by the laser systems. Using data from only the radar’s two less-sensitive conventional pulse modes would increase the missed detections to 22%–34%. A significant remaining problem is that the radar’s lower-altitude data are often contaminated with echoes from nonhydrometeor targets, such as insects.

Full access
Sergey Y. Matrosov, Andrew J. Heymsfield, Robert A. Kropfli, Brooks E. Martner, Roger F. Reinking, Jack B. Snider, Paivi Piironen, and Edwin W. Eloranta

Abstract

Ice cloud microphysical parameters derived from a remote sensing method that uses ground-based measurements from the Environmental Technology Laboratory’s Ka-band radar and an IR radiometer are compared to those obtained from aircraft sampling for the cirrus priority event from the FIRE-II experiment. Aircraft cloud samples were taken not only by traditional two-dimensional probes but also by using a new video sampler to account for small particles. The cloud parameter comparisons were made for time intervals when aircraft were passing approximately above ground-based instruments that were pointed vertically. Comparing characteristic particle sizes expressed in terms of median mass diameters of equal-volume spheres yielded a relative standard deviation of about 30%. The corresponding standard deviation for the cloud ice water content comparisons was about 55%. Such an agreement is considered good given uncertainties of both direct and remote approaches and several orders of magnitude in natural variability of ice cloud parameters. Values of reflectivity measured by the radar and calculated from aircraft samples also showed a reasonable agreement; however, calculated reflectivities averaged approximately 2 dB smaller than those measured. The possible reasons for this small bias are discussed. Ground-based and aircraft-derived particle characteristic sizes are compared to those available from published satellite measurements of this parameter for the cirrus priority case from FIRE-II. Finally, simultaneous and collocated, ground-based measurements of visible (0.523 nm) and longwave IR (10–11.4 μm) ice cloud extinction optical thickness obtained during the 1995 Arizona Program are also compared. These comparisons, performed for different cloud conditions, revealed a relative standard deviation of less than 20%;however, no systematic excess of visible extinction over IR extinction was observed in the considered experimental events.

Full access