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  • Author or Editor: E. J. Zipser x
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R. A. Madden and E. J. Zipser

Abstract

Analysis of serial rawinsonde observations over the Line Islands during March and April 1967 reveals a multi-layered wind structure, especially in the meridional component, which changes sign as many as eight times below 20 km. The layering is strongest above 14 and below 9 km, and is most marked near the equator. Very large vertical wind shears are observed, occurring most frequently near the tropopause. It is likely that the most extreme shears are accompanied by considerable turbulence and may, therefore, represent significant kinetic energy sinks. The layered winds above 14 and below 9 km may be associated with vertically propagating waves. The wind variations in the 9–14 km region appear to be linked to changes in position and intensity of circulation features in either hemisphere rather than with a regular progression of wave disturbances.

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E. J. Zipser and M. A. LeMone

Abstract

The properties of convective drafts and cores are presented in Part I. By our definition a convective updraft must have a positive vertical velocity for 0.5 km, and exceed 0.5 m s−1 for 1 s; a convective updraft core must exceed 1 m s−1 for 0.5 km. Downdrafts and downdraft cores are defined analogously. Here the properties of the drafts and cores are compared to results of previous work. In addition, the implications of the results in Part I are discussed.

GATE cores and drafts are comparable in size and intensity to those measured in hurricanes but weaker than those measured in continental thunderstorms. The lesser intensity seems related to the nearly moist adiabatic GATE sounding. The mass flux by GATE cores is consistent with large-scale requirements. It is fairly evenly distributed over a range of core size and intensity. Updraft core vertical velocity and diameter are positively correlated, primarily the result of a few large strong events.

The vast majority of GATE convective cores are sufficiently weak, with mean vertical velocities < 3–5 m s−1, that the time scale for air starting at cloud base to reach the upper troposphere can be in excess of 1 h. The microphysical implications of such long time scales are discussed. They include large fractional rainout from the warm part of the cloud, the presence of ice at relatively warm temperatures, and rapid decrease of radar reflectivity with height above the 0°C level.

Usually the clouds in GATE were part of a larger, organized mesoscale system. The typical distribution of cumulonimbus clouds, cores and drafts in such a system is synthesized by combining our results with other GATE results. A schematic updraft core and downdraft core in the middle troposphere are presented, emphasizing that these entities were rather narrow and weak in GATE clouds.

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G. M. Barnes, E. J. Zipser, D. Jorgensen, and F. Marks Jr.

Abstract

The mesoscale thermodynamic, kinematic, and radar structure of a Hurricane Floyd rainband observed on 7 September 1981 is presented. Data are from 26 aircraft passes through the rainband from 150 to 6400 m. A composite technique which presents rainband structure as a function of distance from the storm circulation center reveals inflow from the outer edge of the band and a partial barrier to this flow below 3 km. In the direction parallel to rainband orientation, radar reveals cellular reflectivity structure on the upwind and central portions of the rainband; the frequency of cellular precipitation decreases in favor of stratiform precipitation further downwind as the band spirals gradually towards the eyewall. In the radial direction, a decrease of 12 K in θe, is observed across the rainband in the subcloud layer. Convective scale up- and downdrafts that are associated with cellular reflectivity structure are hypothesized to be responsible for the thermodynamic modification of the cloud and subcloud layers.

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Robbie E. Hood, Daniel J. Cecil, Frank J. LaFontaine, Richard J. Blakeslee, Douglas M. Mach, Gerald M. Heymsfield, Frank D. Marks Jr., Edward J. Zipser, and Michael Goodman

Abstract

During the 1998 and 2001 hurricane seasons of the western Atlantic Ocean and Gulf of Mexico, the Advanced Microwave Precipitation Radiometer (AMPR), the ER-2 Doppler (EDOP) radar, and the Lightning Instrument Package (LIP) were flown aboard the NASA ER-2 high-altitude aircraft as part of the Third Convection and Moisture Experiment (CAMEX-3) and the Fourth Convection and Moisture Experiment (CAMEX-4). Several hurricanes, tropical storms, and other precipitation systems were sampled during these experiments. An oceanic rainfall screening technique has been developed using AMPR passive microwave observations of these systems collected at frequencies of 10.7, 19.35, 37.1, and 85.5 GHz. This technique combines the information content of the four AMPR frequencies regarding the gross vertical structure of hydrometeors into an intuitive and easily executable precipitation mapping format. The results have been verified using vertical profiles of EDOP reflectivity and lower-altitude horizontal reflectivity scans collected by the NOAA WP-3D Orion radar. Matching the rainfall classification results with coincident electric field information collected by the LIP readily identifies convective rain regions within the precipitation fields. This technique shows promise as a real-time research and analysis tool for monitoring vertical updraft strength and convective intensity from airborne platforms such as remotely operated or uninhabited aerial vehicles. The technique is analyzed and discussed for a wide variety of precipitation types using the 26 August 1998 observations of Hurricane Bonnie near landfall.

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E. A. Smith, J. E. Lamm, R. Adler, J. Alishouse, K. Aonashi, E. Barrett, P. Bauer, W. Berg, A. Chang, R. Ferraro, J. Ferriday, S. Goodman, N. Grody, C. Kidd, D. Kniveton, C. Kummerow, G. Liu, F. Marzano, A. Mugnai, W. Olson, G. Petty, A. Shibata, R. Spencer, F. Wentz, T. Wilheit, and E. Zipser

Abstract

The second WetNet Precipitation Intercomparison Project (PIP-2) evaluates the performance of 20 satellite precipitation retrieval algorithms, implemented for application with Special Sensor Microwave/Imager (SSM/I) passive microwave (PMW) measurements and run for a set of rainfall case studies at full resolution–instantaneous space–timescales. The cases are drawn from over the globe during all seasons, for a period of 7 yr, over a 60°N–17°S latitude range. Ground-based data were used for the intercomparisons, principally based on radar measurements but also including rain gauge measurements. The goals of PIP-2 are 1) to improve performance and accuracy of different SSM/I algorithms at full resolution–instantaneous scales by seeking a better understanding of the relationship between microphysical signatures in the PMW measurements and physical laws employed in the algorithms; 2) to evaluate the pros and cons of individual algorithms and their subsystems in order to seek optimal “front-end” combined algorithms; and 3) to demonstrate that PMW algorithms generate acceptable instantaneous rain estimates.

It is found that the bias uncertainty of many current PMW algorithms is on the order of ±30%. This level is below that of the radar and rain gauge data specially collected for the study, so that it is not possible to objectively select a best algorithm based on the ground data validation approach. By decomposing the intercomparisons into effects due to rain detection (screening) and effects due to brightness temperature–rain rate conversion, differences among the algorithms are partitioned by rain area and rain intensity. For ocean, the screening differences mainly affect the light rain rates, which do not contribute significantly to area-averaged rain rates. The major sources of differences in mean rain rates between individual algorithms stem from differences in how intense rain rates are calculated and the maximum rain rate allowed by a given algorithm. The general method of solution is not necessarily the determining factor in creating systematic rain-rate differences among groups of algorithms, as we find that the severity of the screen is the dominant factor in producing systematic group differences among land algorithms, while the input channel selection is the dominant factor in producing systematic group differences among ocean algorithms. The significance of these issues are examined through what is called “fan map” analysis.

The paper concludes with a discussion on the role of intercomparison projects in seeking improvements to algorithms, and a suggestion on why moving beyond the “ground truth” validation approach by use of a calibration-quality forward model would be a step forward in seeking objective evaluation of individual algorithm performance and optimal algorithm design.

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