Much of the rain that falls in the deep tropics is concentrated in the inter-tropical convergence zone (ITCZ). The dynamics that determine the distribution of convective rainfall near the equator, such as the position of the inter-tropical convergence zone (ITCZ), are not well understood. Global climate models (GCMs) often fail to capture the observed distribution, and it is sensitive to details of model parameterizations. Observational evidence suggests that a fundamental fluid dynamical instability, inertial instability, is important for this problem. Here the problem of the position of the ITCZ will be addressed by focusing on the role of inertial instability within the boundary layer - the atmospheric layer near the ground - and interactions between inertial instability and boundary-layer turbulence and convection. Dynamical hypotheses will be tested using boundary-layer parameterizations driven by data. The key data are scatterometer (QuikSCAT) derived winds and wind stresses. Processes inferred from the observational studies will be tested in a set of model experiments.
Three major tasks will be carried out: 1) Analyses of observational data to investigate the relationship between the inertial instability - specifically the location of the line of zero absolute vorticity - and the location of the ITCZ. 2) Analyses of the force balances within the boundary layer, and the transition from advective to Ekman (drag dominated) regimes across the line of zero absolute vorticity. 3) Analyses of the time scales of inertial instability and the processes that contribute to the position of the ITCZ on different timescales
Broader impacts of this research are in its potential to drive improved representations of tropical circulations in global models, improved understanding of the Indian monsoon and of the genesis of tropical cyclones, and in the application of some methods to related problems that involve modeling sub-grid scale processes. A new investigator will be trained and an undergraduate will participate in the research through cooperation with the University of Washington.
The main scientific objectives of the study were to understand how the ocean and atmosphere interact to determine the tropical climate and weather and how specific weather and climate phenomena in the Asian monsoon region organize. In spite of years of development, weather and coupled ocean-atmosphere climate models have difficulties in simulating fundamental aspects of the tropical weather and climate, especially those of precipitation systems. Although when averaged over longer terms, the climate is sometimes simulated reasonably well, the day-to-day and intraseasonal variations are poorly simulated, especially in the Indian and western Pacific Oceans, where very few local observations for model validation exist. This has deleterious effect on economic and emergency forecasting in this most populated, fastest growing, and economically viable tropical region of the world. In contrast with the scarcity of sea-based observations, earth-observing satellites provide massive amounts of data that can be hard to analyze. This presents a double challenge to scientists: a deluge of information from satellites with no or very few ground-based observations or reliable model outputs for validation. Our research collected and analyzed data in order to provide guidance for future climate modeling, and at the same time developed data mining methods to effectively process and validate the massive satellite data, detect patterns and trends, and combine heterogeneous data to drive models (a.k.a. data assimilation). We were involved with two field campaigns at sea. Observations taken on board ships in these campaigns were used for calibration of satellite sensors. Our data analysis and mining focused on establishing the life cycle of large-scale precipitation systems and how they depend on cross-equatorial winds. This included establishing a preliminary classification of how large-scale precipitation systems get organized in different ocean basins at different phases of the monsoon, and the discovery of organization patterns not observed before. Our research improved the understanding of the monsoon in the Indian Ocean basin, how it is different from other (better studied) basins, and how it affects the distribution of wind, rain and ocean currents. It also contributed to the understanding of off-equatorial tropical storm evolution (Typhoons and Hurricanes). This project enabled us to maintain a training, development, and outreach program, and a visitor program for U.S. and overseas scientists and students. It helped establish an early career scientist who was also involved with undergraduate teaching and teachers’ training; allowed the principal investigator to co-organize and teach in two capacity building courses and supported the participation of US scientists and students, under-represented in the science and engineering, in international meetings. Important collaborations, which included training students in data collection and participation in two international field programs, have been. We established science collaborations with the Indian Space Research Organization (ISRO), the Chinese Academy of Sciences, secured data allocation from the Indian Oceansat-2 satellite, and were invited to participate in a Chinese oceanographic research cruise. Unique data have been collected for future use, and several science publications have appeared or are forthcoming as a result. In addition to ongoing collaborations with students, postdocs, and visitors, results were presented at national and international meetings. The principal investigator also organized related special sessions at two international conferences, served as an editor of 3 special issues of an international journal (IJRS) and as co-editor of two books. As part of a related Research Education for Undergraduates supplement, meaningful research experience and tutoring were provided to an undergraduate student (Andrew Geiss), who participated and gave his first presentation in an international conference in 2010, won a student paper award at the 91st American Meteorological Society annual meeting, was involved in preliminary field data analysis, and co-authored two peer-reviewed papers. This study, through synergy with other programs, also bridged the gap between advancements made in different disciplines. The main focus of our Chinese collaborators has been on the effects of monsoon conditions on marine ecosystems. Our collaboration has broadened the scope of both the Chinese study and our own into other disciplines: We expended use of the data taken by the Chinese, ensuring that data relevant to meteorological and ocean-atmosphere interactions are properly taken and used, while at the same time providing interdisciplinary use of our data for the study of marine ecosystems. An urgent need of field observations in the tropical Indian Ocean had been recognized as an International, US and NSF priority. The observations by the Chinese field campaigns will complement and enhance those taken during another US/International field campaign we participated in (DYNAMO), shading light on different seasons. Finally, involvement with planning, editing, and publications through our ongoing outreach activities and through participation in international science teams and committees, and involving students in international field campaigns have significant broader impacts that will be sustained in the long term.
