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This study focuses on track and intensity changes of three tropical cyclones that, during the season of 2006, developed in the eastern North Pacific basin and made landfall over northwestern Mexico. Observational dataseis, including satellite and radar imagery and a rain gauge network, are used to document regional-scale structures. Additionally, gridded fields are applied to determine the large-scale environment. John made landfall as a category-2 hurricane on the Saffir-Simpson scale and moved along the Baja California Peninsula during more than 40 h, resulting in total rainfall of up to 506 mm. The largest accumulations were located over mountains and set new records with respect to daily rates from the 1969-2005 period. Later in the season. Lane and Paul made landfall over the mainland and brought moderate rainfall over the coastal plains. Lane became a category-3 hurricane and was the third strongest hurricane to make landfall since 1969. In contrast, Paul followed a recurving track to reach the coastline as a weakening tropical depression. Strong wind shear, associated with a midlatitude trough, is found to be related to the intensity change. Examination of the official forecasts reveals that first inland positions were predicted several days before the actual landfall events. An assessment of the forecasts issued 1-3 days prior to landfall shows large track errors associated with some of the above tropical cyclones and this resulted in a westward bias. It is sug-gested that the track errors are due to an inadequate representation of the large-scale environment that steered the tropical cyclones. [ABSTRACT FROM AUTHOR]

Statistical analysis of the vertical structure of radar echoes in the eyewalls of tropical cyclones, shown by the Tropical Rainfall Measurement Mission (TRMM) Precipitation Radar (PR), shows that the eyewall contains high reflectivities and high echo tops, with deeper and more intense but highly intermittent echo perturbations superimposed on the basic structure. The overall echo strength, height of echo top, and presence of intense echo perturbations all increase with vortex strength. Intense echo perturbations decrease in frequency with low sea surface temperatures. When the PR data are normalized by the amount of radar echo in each sample and examined quadrant by quadrant relative to the direction of the environmental shear, the nature of convective processes in different parts of the eyewall becomes apparent. The normalized statistics of the echo intensity, brightband structure, and maximum echo-top height show that processes generating convective precipitation are generally favored in the downshear-right region of the eyewall, while the nonnormalized statistics indicate that the vertical wind shear determines the placement of precipitation particles downwind of the generation zone such that the precipitation maximum occurs about one quadrant downwind of the convective generation zone. When the track speed exceeds the magnitude of the shear vector, this pattern modifies such that the asymmetry rotates one quadrant to the right. The statistics, moreover, indicate that vertical wind shear is the factor determining the placement of precipitation particles around the storm, while other factors determine the location, intensity, and means of their generation. [ABSTRACT FROM AUTHOR]

A global study of the vertical structures of the clouds of tropical mesoscale convective systems (MCSs) has been carried out with data from the CloudSat Cloud Profiling Radar. Tropical MCSs are found to be dominated by cloud-top heights greater than 10 km. Secondary cloud layers sometimes occur in MCSs, but outside their primary raining cores. The secondary layers have tops at 6--8 and 1--3 km. High-topped clouds extend outward from raining cores of MCSs to form anvil clouds. Closest to the raining cores, the anvils tend to have broader distributions of reflectivity at all levels, with the modal values at higher reflectivity in their lower levels. Portions of anvil clouds far away from the raining core are thin and have narrow frequency distributions of reflectivity at all levels with overall weaker values. This difference likely reflects ice particle fallout and therefore cloud age. Reflectivity histograms of MCS anvil clouds vary little across the tropics, except that (i) in continental MCS anvils, broader distributions of reflectivity occur at the uppermost levels in the portions closest to active raining areas; (ii) the frequency of occurrence of stronger reflectivity in the upper part of anvils decreases faster with increasing distance in continental MCSs; and (iii) narrower-peaked ridges are prominent in reflectivity histograms of thick anvil clouds close to the raining areas of connected MCSs (superclusters). These global results are consistent with observations at ground sites and aircraft data. They present a comprehensive test dataset for models aiming to simulate process-based upper-level cloud structure around the tropics. [ABSTRACT FROM AUTHOR]

With radar measurements and temporally high-resolution surface observations, this study investigates surface fluctuations associated with tropical cyclone rainbands (TCRs) observed in the vicinity of Taiwan during 2000--08. A total of 263 TCRs identified from 37 typhoon events during the study period were analyzed to show the mean and common nature of perturbations of various meteorological variables associated with the passage of TCRs. The main patterns of surface thermodynamic fluctuations, as revealed from the composite analysis of all identified TCRs, include a persistent decrease in temperature, dewpoint temperature, and equivalent potential temperature θθe from the outer to inner edge of the rainband. A wavelike variation of pressure perturbations associated with the rainband was evident, with a minimum coincident with the outer edge and a maximum located inside the inner edge. The kinematics of the rainband was characterized by an obvious decrease in cross-band wind component, relatively minor variations in along-band wind component, and the wind veering. Quantitative analyses indicate that the majority of the TCRs (~80%%--90%%) exhibited variations in surface temperature, pressure, wind speed, and wind direction less than 2°°C, 1.5 mb, 5 m s−−1, and 20°°, respectively. However, a clear trend of the magnitude of TCR thermodynamic fluctuations increasing with the radial distance from the tropical cyclone center was observed. The TCRs identified in this study were also classified into the outer and inner rainbands, which are distinguished by a radial distance of 3 times the radius of maximum wind. The composite and magnitude analyses of their surface fluctuations indicate that the outer rainbands had a higher potential than the inner rainbands to reduce the near-surface θθe values. This observed characteristic is likely related to more pronounced evaporative cooling taking place in drier subcloud regions and the downward transport of low- θθe air aloft by more vigorous convective downdrafts for the outer rainband. Fundamentally different features of surface pressure fluctuations and mean frictional vertical velocity and relative vorticity between the outer and inner rainbands were also documented. These results reflect a possibly different origin. Nevertheless, there was no dramatic difference in the pattern of kinematic fluctuations between the outer and inner rainbands, and their mean magnitudes were also found to be statistically identical, which suggests that there is not an entirely clear distinction of surface characteristics for these two types of rainbands. [ABSTRACT FROM AUTHOR]

The dual-polarization weather radar on the Kwajalein Atoll in the Republic of the Marshall Islands (KPOL) is one of the only full-time (24/7) operational S-band dual-polarimetric (DP) radars in the tropics. Through the use of KPOL DP and disdrometer measurements from Kwajalein, quality control (QC) and reflectivity calibration techniques were developed and adapted for use. Data studies in light rain show that KPOL DP measurements are of sufficient quality for these applications. While the methodology for the development of such applications is well documented, the tuning of specific algorithms to the particular regime and observed raindrop size distributions requires a comprehensive testing and adjustment period. Presented are algorithm descriptions and results from five case studies in which QC and absolute reflectivity calibration were performed and assessed. Also described is a unique approach for calibrating the differential reflectivity field when vertically pointing observations are not available. Results show the following: 1) DP-based QC provides superior results compared to the legacy Tropical Rainfall Measuring Mission (TRMM) QC algorithm (based on height and reflectivity thresholds), and 2) absolute reflectivity calibration can be performed using observations of light rain via a published differential phase--based integration technique; results are within ±±1 dB compared to independent measurements. Future extension of these algorithms to upgraded Weather Surveillance Radar-1988 Doppler (WSR-88D) polarization diverse radars will benefit National Aeronautics and Space Administration''s (NASA''s) Precipitation Measurement Missions (PMM) validation programs. [ABSTRACT FROM AUTHOR]

A method is introduced for stochastic rainfall downscaling that can be easily applied to the precipitation forecasts provided by meteorological models. Our approach, called the Rainfall Filtered Autoregressive Model (RainFARM), is based on the nonlinear transformation of a Gaussian random field, and it conserves the information present in the rainfall fields at larger scales. The procedure is tested on two radar-measured intense rainfall events, one at midlatitude and the other in the Tropics, and it is shown that the synthetic fields generated by RainFARM have small-scale statistical properties that are consistent with those of the measured precipitation fields. The application of the disaggregation procedure to an example meteorological forecast illustrates how the method can be implemented in operational practice. [ABSTRACT FROM AUTHOR]