Meteorology 6310 Tropical Meteorology

Theme of the course: Develop physical understanding of tropical phenomena over a range of scales. Using observed characteristics as the starting point, we include small scale (cumulus clouds, thunderstorms), mesoscale (sea breezes, squall lines), large scale (waves and cyclones), and planetary scale circulations (trade winds, equatorial trough, equatorial waves, monsoons, intraseasonal oscillation, El-Nino/Southern Oscillation). In studying each class of events, we learn the importance of understanding how physical processes on one scale influence those on other scales. We shall appreciate how understanding convective and mesoscale processes in the tropics helps us understand them better in mid latitudes. The hurricane will be a frequent subject of study, partly because of its intrinsic importance, and partly because it serves as an excellent example of the interactions between small and large scale processes.

One of the purposes of the course is to learn how to obtain information from many sources. Tropical meteorology is a subject of huge breadth. It is a challenge for the student and professor alike to summarize well-accepted principles and facts (and find them in textbooks). Often, we will go directly to the literature and try to understand samples of work in progress. There are now some excellent tools such as web-based databases which will be used frequently. The individual projects are intended to give the student hands-on experience in searching and evaluating the literature on some topics of interest.

We shall begin by taking advantage of being within the hurricane season, and "jump right in", using available technology on various web sites to view tropical cyclones and their environments. We shall practice using different data sources, conventional and experimental, like the microwave products from SSM/I and TMI (TRMM microwave imagers). We will also use the traditional lecture format, reviewing tropical climatology, fundamental physical processes, planetary boundary layer, energy transfers, disturbances on all scales, and hurricanes. Early in the course, before we have covered the lecture material, these real-time examples will be like the early pages of a mystery novel the pieces will NOT seem to fit together. But the goal will be that by the end of the course they will make a more coherent story.

Text: None. Materials will handed out from time to time.

Exams and Grades: No exams. Grades will be based a term project, classroom participation, and occasional problem sets.

Approximate Course Outline:

• Concepts of Scale. Units, dimensions, typical values of horizontal and vertical wind, rain rate, etc., as function of scale (recurring throughout course).

• Observational Basis. Data distribution; routine, and field programs. Basic principles of operation and interpretation of microwave data from SSM/I and TRMM, and contrast with more familiar images from VIS/IR. Availability and uses of lightning data. Some differences between in situ and remote sensing. (recurring throughout course)

• Tropical cyclones and hurricanes. Structure and dynamics of the hurricane. Measurement methods, surface vs aircraft winds, climatology, genesis (so many chances, so few hurricanes), eyewall, rainbands, eyewall replacement cycles, tracks, extratropical transitions, impacts on the coastline and inland, physical processes, sea-air interactions, concepts of scale interaction in formation and maintenance of the hurricane. Why did modification experiments prove so disappointing? Early in the course, we will mainly follow examples in real time as they happen. Later, we will return to the hurricane in a more systematic review, in the light of almost all other elements of the course.

• Large Scale Characteristics of the Tropics. Overview of large scale time averaged circulation. Distributions of wind, pressure, temperature, and rainfall. Examples of annual cycles at locations. Eastern vs.western oceans. Land vs. ocean. Subtropical high, trades and trade inversion, equatorial trough / ITCZ, Hadley cells. Monsoons, large scale tropical waves, intraseasonal and interseasonal oscillations, ENSO, QBO.

• Basic Physics. Structure of the planetary boundary layer, sea-air transfer of momentum, heat, and moisture, and transfer through the subcloud and cloud layers. Cumulus and cumulonimbus clouds -- observed properties of convective clouds over land and ocean, and attempts to explain observations with parcel theory. Relevance and importance of cloud microphysics.

• Diurnal Variations, Local, Regional, and Terrain Effects. Coastlines, land/sea breezes, mountain/valley circulations, and their dependence upon stability and flow regimes. Effects on rainfall.

• Tropical Disturbances Across the Scale Spectrum. Clouds, rainstorms, severe storms, mesoscale systems, synoptic systems, large scale waves, 30-60-day wave, monsoons, El Nino. Use and abuse of mass, heat, energy budget studies. Look at interrelationships. Brief look at synoptic models, tropical analysis and forecasting procedures: how well do they work?