Abstract ATM-9422512 Newell, Reginald Massachusetts Institute of Technology Title: Physical Mechanisms Contributing to Climate Variability This project seeks to understand how changes in processes involving water in its various forms influence changes in the climate system. Through evaporation at the ocean surface solar energy is converted into latent heat then transported as such within the atmosphere. When the water vapor condenses and precipitation occurs the latent heat is released in to the atmosphere. While the water vapor is being transported in the atmosphere it undergoes radiative cooling in the infrared as well as absorbing solar radiation in the near infrared Water vapor therefore plays a major role in the energy budget of the atmosphere. It has been found that water vapor is transported from one place to another in the atmosphere in the form of relatively long (10,000-12,000 km) relatively thin (~400-500km wide) filaments which may be termed atmospheric rivers. These filaments are often entrained into low pressure systems with the result that the low pressure systems deepen. One of the main objectives of this work is to understand from detailed grid point data provided by the European Center for Medium-range Weather Forecasts (ECMWF) how the rivers form, how they influence cyclone development, how their paths vary from year to year, how the injection of energy they bring to middle latitudes influences waves patterns there and how they are modified during interannual, interdecadal and ice-age changes. It has been found that rivers are important components of rapidly developing cyclones termed "bombs." The interaction of these two phenomena will be studied. The river brings a pulse of latent heat into the cyclone system. When more details about the river phenomena are understood a numerical model of it will be constructed. Several new data sets from satellites will be collected that may help in defining the positions of rivers over the globe. These includ e satellites that measure column water vapor contents like SSM/I, GPS/MET and ERs-1 and 2 as well as satellites that measure rainfall patterns over the ocean. Such patterns show evidence of water vapor flux convergence and may be treated as indicators of the leading edges of rivers. Standard rainfall data may be used to monitor the leading edges over land masses. One interpretation of floods is that rivers which normally produce water vapor flux convergence occasionally, in certain regions, are channelled into preferred paths during a flood regime. To use this concept the climatology of river patterns must be described from as long a data set as possible. Five years of ECMWF data is proposed to be used for this purpose; the work may be carried back in time (~15 years) once the reanalyzed data sets are available. This approach will be applied to two recent examples of floods; the Mississippi flood of summer 1993 and the Hong-Kong-South China flood of summer 1994. The latter produced 1-2 meters of rain in about three week, by far the largest amount since records began in 1884. If it turns out that floods are related to river positions in this manner then it is obviously necessary to find out what controls these positions. Patterns of cold fronts and divergent wind components in the lower atmosphere, association with El Nino, relationships with potential vorticity patterns and upper troposphere water vapor all will be studied. Climate fluctuations are being studied from data sets on surface ocean wind, temperature and relative humidity obtained from ships report. The reports are used to estimate the flux of energy between the atmosphere and the ocean. The seasonal and non-seasonal modes of variation of sea-air energy exchange are being related to sea surface temperature and free air temperature, non-seasonal anomalies in an effort to understand why there is a strong linkage between these fluctuations. As the main ocean-atmosphere energy transfer term is latent heat and the main heating rate for the free troposphere is latent heat liberation, the river concept is useful because it connects these two regions. If the rainfall patterns due to rivers can be isolated, empirical orthogonal function analysis can be used to study seasonal and non-seasonal changes in the convergent and divergent regions and related to those already discussed as atmospheric modes. There exist a number of temperature limits in the climate system and work is under way to find the physical mechanisms that control these limits. Cloud and moisture data are also being studied in conjunction with a radiative transfer program as the limits appear to involve a number of physical factors. This research is important because it seeks to improve understanding of major processes that affect climate variability and change.
