[1] This paper presents analyses of five tropical disturbances of various types, derived from observations made over the northwest Pacific in August and September of 2008. Various dynamic and thermodynamic products were derived from dropsonde and airborne Doppler radar data, with the goal of increasing our understanding of tropical cyclogenesis. From these analyses we draw the following tentative conclusions: The formation of a strong midlevel circulation, with its associated cold core at low levels and warm core aloft, greatly aids the spin-up of a tropical cyclone by changing the vertical mass flux profile of deep convection from top heavy to bottom heavy. This has two effects: (1) the enhancement at low levels of the convergence of mass and hence vorticity, thus aiding the spin-up of a warm-core vortex and (2) the suppression of the lateral export of moist entropy by deep convective inflows and outflows from the core of the developing system. This allows the relative humidity to build up, resulting in more intense convection and further development. Our results also suggest that strong horizontal strain rate at middle levels, as measured by a form of the Okubo-Weiss parameter, is detrimental to tropical cyclogenesis. Not only can such flow tear apart the midlevel vortex, it can also import air with low moist entropy. In our small sample, the Okubo-Weiss parameter was the best indicator of the potential for development. Vertical shear appeared to play a less important role in the systems we investigated.
Abstract. The formation of west Pacific tropical cyclone Nuri (2008) was observed over four days from easterly wave to typhoon stage by aircraft using scanning Doppler radar and dropsonde data. This disturbance developed rapidly in a significantly sheared environment. In spite of the shear, overlapping closed circulations existed in the frame of reference of the storm in the planetary boundary layer and at 5 km elevation, providing a deep region protected from environmental influences. The rapid spinup of Nuri can be attributed to the strong increase with height at low levels of the vertical mass flux during and after the tropical depression stage, and the correspondingly strong vorticity convergence in the planetary boundary layer. As Nuri developed, convective regions of boundary layer vortex stretching became fewer but more intense, culminating in a single nascent eyewall at the tropical storm stage. A non-developing tropical wave case was also analyzed. This system started with much weaker circulations in the boundary layer and aloft, leaving it unprotected against environmental intrusion. This may explain its failure to develop.
Direct diagnostic evaluation of the moisture tendency in the moisture equation is very difficult in practice because two poorly measured terms, moisture convergence and precipitation, dominate the equation. Using the near constancy in space and time of the tropical temperature profile, a variety of energy and entropy based equations have been employed to obtain indirect estimates of the moisture budget. In this paper rigorous versions of the energy and entropy equations are developed. The strengths and weakness of these two formulations are complementary, allowing the authors to estimate moistening and drying tendencies with high confidence when the two formulations are used together. This study applies the theory to data from Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). The results demonstrate how convection regulates the tropospheric humidity, drying the atmosphere when it becomes too moist, and moistening it when it becomes too dry.
Abstract. In this work, we describe an efficient approach for wind retrieval from dual Doppler radar data. The approach produces a gridded field that not only satisfies the observations, but also satisfies the anelastic mass continuity equation.The method is based on the so-called three-dimensional variational approach to the retrieval of wind fields from radar data. The novelty consists in separating the task into steps that reduce the amount of data processed by the global minimization algorithm, while keeping the most relevant information from the radar observations. The method is flexible enough to incorporate observations from several radars, accommodate complex sampling geometries, and readily include dropsonde or sounding observations in the analysis.We demonstrate the usefulness of our method by analyzing a real case with data collected during the TPARC/TCS-08 field campaign.
In this work, we describe an efficient approach for wind retrieval from dual Doppler radar data. The approach produces a gridded field that not only satisfies the observations, but also satisfies the anelastic mass continuity equation. <br><br> The method is based on the so-called three-dimensional variational approach to the retrieval of wind fields from radar data. The novelty consists in separating the task into steps that reduce the amount of data processed by the global minimization algorithm, while keeping the most relevant information from the radar observations. The method is flexible enough to incorporate observations from several radars, accommodate complex sampling geometries, and readily include dropsonde or sounding observations in the analysis. <br><br> We demonstrate the usefulness of our method by analyzing a real case with data collected during the TPARC/TCS-08 field campaign
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