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Baode Chen, Wen-wen Tung, and Michio Yanai

1. Introduction The perturbation kinetic energy (PKE) is extensively used to measure and study transient wave activity in the tropics (e.g., Webster and Chang 1988 ; Arkin and Webster 1985 ; Chen and Yanai 2000 ; Yanai et al. 2000 ). Murakami and Unninayar (1977) showed that the region of maximum PKE along the equator in January and February of 1971 was located in the vicinity of the equatorial westerlies. Using National Meteorological Center (NMC) operational tropical objective analyses

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Gary Barnes

Abstract

No Abstract available.

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Yukari N. Takayabu, George N. Kiladis, and Victor Magaña

of the interaction between the cloud scale and the large scale remained a primary focus of Michio’s interest throughout the rest of his career. Fig . 3-1. The scales of tropospheric motions in the tropics, taken from the February 1970 GARP technical report. Adopted from Sikdar and Suomi (1971) . It was remarkably prescient that at the design stage of the GARP Atlantic Tropical Experiment (GATE), Michio selected the word “cloud cluster” to refer to a grouping of cumulonimbus, as a key ingredient

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Steven K. Esbensen, Jan-Hwa Chu, Wen-wen Tung, and Robert G. Fovell

Study Group on Tropical Disturbances in 1968, together with Professors Pisharoty (India) and Fujita (University of Chicago). The group met over the period of a month at the University of Wisconsin to conduct a census of cloud systems in the global tropics using geostationary satellite pictures, and to formulate the scientific requirements for the tropical GARP subprogram. The group classified cloud systems into “cloud clusters,” “monsoon clusters,” and “popcorn cumulonimbi.” They recommended the

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Andrew J. Heymsfield, Martina Krämer, Anna Luebke, Phil Brown, Daniel J. Cziczo, Charmaine Franklin, Paul Lawson, Ulrike Lohmann, Greg McFarquhar, Zbigniew Ulanowski, and Kristof Van Tricht

expected from the results of other sources. Using CALIPSO data, Nazaryan et al. (2008) show that the maximum-occurrence frequency of up to 70% is found near the tropics over the 100°–180°E longitude band. They found a large latitudinal movement of cirrus cloud cover with the changing seasons. The examination of the vertical distribution of cirrus clouds shows the maximum of cirrus top-altitude occurrence frequency of approximately 11% at 16 km in the tropics. Fig . 2-2. Global distribution of

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A. Korolev, G. McFarquhar, P. R. Field, C. Franklin, P. Lawson, Z. Wang, E. Williams, S. J. Abel, D. Axisa, S. Borrmann, J. Crosier, J. Fugal, M. Krämer, U. Lohmann, O. Schlenczek, M. Schnaiter, and M. Wendisch

from the tropics to the poles, are associated with multiple cloud types and meteorological conditions, and can occur throughout the year in all seasons. Global quantitative estimates of the prevalence of mixed-phase clouds are difficult because of the limited data from airborne probes, the small geographic coverage of ground-based remote sensing sites, and the uncertainty in phase detection from satellite remote sensors, especially over high latitudes. Nevertheless, depolarization measurements from

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Carl Wunsch and Raffaele Ferrari

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The central change in understanding of the ocean circulation during the past 100 years has been its emergence as an intensely time-dependent, effectively turbulent and wave-dominated, flow. Early technologies for making the difficult observations were adequate only to depict large-scale, quasi-steady flows. With the electronic revolution of the past 50+ years, the emergence of geophysical fluid dynamics, the strongly inhomogeneous time-dependent nature of oceanic circulation physics finally emerged. Mesoscale (balanced), submesoscale oceanic eddies at 100-km horizontal scales and shorter, and internal waves are now known to be central to much of the behavior of the system. Ocean circulation is now recognized to involve both eddies and larger-scale flows with dominant elements and their interactions varying among the classical gyres, the boundary current regions, the Southern Ocean, and the tropics.

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Robert F. Adler, Christian Kummerow, David Bolvin, Scott Curtis, and Chris Kidd

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Three years of Tropical Rainfall Measuring Mission (TRMM) monthly estimates of tropical surface rainfall are analyzed to document and understand the differences among the TRMM-based estimates and how these differences relate to the pre-TRMM estimates and current operational analyses. Variation among the TRMM estimates is shown to be considerably smaller than among a pre-TRMM collection of passive microwave-based products. Use of both passive and active microwave techniques in TRMM should lead to increased confidence in converged estimates.

Current TRMM estimates are shown to have a range of about 20% for the tropical ocean as a whole, with variations in heavily raining ocean areas of the Intertropical Convergence Zone (ITCZ) and South Pacific Convergence Zone (SPCZ) having differences over 30%. In midlatitude ocean areas the differences are smaller. Over land there is a distinct difference between the Tropics and midlatitude with a reversal between some of the products as to which tends to be relatively high or low. Comparisons of TRMM estimates with ocean atoll and land rain gauge information point to products that might have significant regional biases. The bias of the radar-based product is significantly low compared with atoll rain gauge data, while the passive microwave product is significantly high compared to rain gauge data in the deep Tropics.

The evolution of rainfall patterns during the recent change from intense El Niño to a long period of La Niña and then a gradual return to near neutral conditions is described using TRMM. The time history of integrated rainfall over the tropical oceans (and land) during this period differs among the passive and active microwave TRMM estimates.

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Edward J. Zipser

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The “hot tower” hypothesis requires the existence of deep cumulonimbus clouds in the deep Tropics as essential agents, which accomplish the mass and energy transport essential for the maintenance of the general circulation. As the role of the deep convective clouds has been generally accepted, the popularity of referring to these deep “hot” towers as undilute towers also has gained acceptance. This paper examines the consequences of assuming that the deep convective clouds over tropical oceans consist of undilute ascent from the subcloud layer.

Using simple applications of parcel theory, it is concluded that observed properties of typical cumulonimbus updrafts in low- to midtroposphere over tropical oceans are inconsistent with the presence of undilute updrafts. Such undilute updrafts are far more consistent with observations in severe storms of midlatitudes. The observations over tropical oceans can be hypothetically explained by assuming large dilution of updrafts by entrainment below about 500 hPa, followed by freezing of condensate. This freezing and subsequent ascent along an ice adiabat reinvigorates the updrafts and permits them to reach the tropical tropopause with the necessary high values of moist static energy, as the hot tower hypothesis requires. The large difference observed between ocean and land clouds can be explained by assuming slightly smaller entrainment rates for clouds over land. These small entrainment differences have a very large effect on updrafts in the middle and upper troposphere and can presumably account for the large differences in convective vigor, ice scattering, and lightning flash rates that are observed. It follows that convective available potential energy (CAPE) is not a particularly good predictor of the behavior of deep convection.

Using the Tropical Rainfall Measuring Mission (TRMM) to map a proxy for the most intense storms on earth between 36°S and 36°N, they are found mostly outside the deep Tropics, with the notable exception of tropical Africa.

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Eric A. Smith and Throy D. Hollis

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Currently, satellite algorithms are the methodology showing most promise for obtaining more accurate global precipitation estimates. However, a general problem with satellite methods is that they do not measure precipitation directly, but through inversion of radiation–rain relationships. Because of this, procedures are needed to verify algorithm-generated results. The most common method of verifying satellite rain estimates is by direct comparison with ground truth data derived from measurements obtained by rain gauge networks, ground-based weather radar, or a combination of the two. However, these types of comparisons generally shed no light on the physical causes of the differences. Moreover, ground validation measurements often have uncertainty magnitudes on the order of or greater than the satellite algorithms, motivating the search for alternate approaches. The purpose of this research is to explore a new type of approach for evaluating and validating the level-2 Tropical Rainfall Measuring Mission (TRMM) facility rain profile algorithms. This is done by an algorithm-to-algorithm intercomparison analysis in the context of physical hypothesis testing.

TRMM was launched with the main purpose of measuring precipitation and the release of latent heat in the deep Tropics. Its rain instrument package includes the TRMM Microwave Imager (TMI), the Precipitation Radar (PR), and the Visible and Infrared Scanner (VIRS). These three instruments allow for the use of combined-instrument algorithms, theoretically compensating for some of the weaknesses of the single-instrument algorithms and resulting in more accurate estimates of rainfall. The focus of this research is on the performance of four level-2 TRMM facility algorithms producing rain profiles using the TMI and PR measurements with both single-instrument and combined-instrument methods.

Beginning with the four algorithms' strengths and weaknesses garnered from the physics used to develop the algorithms, seven hypotheses were formed detailing expected performance characteristics of the algorithms. Procedures were developed to test these hypotheses and then applied to 48 storms from all ocean basins within the tropical and subtropical zones over which TRMM coverage is available (∼35°N–35°S). The testing resulted in five hypotheses verified, one partially verified, and one inconclusive. These findings suggest that the four level-2 TRMM facility profile algorithms are performing in a manner consistent with the underlying physical limitations in the measurements (or, alternatively, the strengths of the physical assumptions), providing an independent measure of the level-2 algorithms' validity.

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