Quasi-hydrostatic Primitive Equations for Ocean Global Circulation Models

Global existence of weak and strong solutions to the quasi-hydrostatic primitive equations is studied in this paper. This model, that derives from the full non-hydrostatic model for geophysical fluid dynamics in the zero-limit of the aspect ratio, is more realistic than the classical hydrostatic model, since the traditional approximation that consists in neglecting a part of the Coriolis force is relaxed. After justifying the derivation of the model, the authors provide a rigorous proof of global existence of weak solutions, and well-posedness for strong solutions in dimension three.

An extended variable-grid global ocean circulation model and its preliminary results of the equatorial Pacific circulation

To investigate the interaction between the tropical Pacific and China seas a variable-grid global ocean circulation model with fine grid covering the area from 20°S to 50°N and from 99° to 150°E is developed. Numerical computation of the annually cyclic circulation fields is performed. The results of the annual mean zonal currents and deep to abyssal western boundary currents in the equatorial Pacific Ocean are reported. The North Equatorial Current,the North Equatorial Countercurrent, the South Equatorial Current and the Equatorial Undercurrent are fairly well simulated. The model well reproduces the northward flowing abyssal western boundary current.From the model results a lower deep western boundary current east of the Bismarck-Solomon-New Hebrides Island chain at depths around 2 000 m has been found. The model results also show that the currents in the equatorial Pacific Ocean have multi-layer structures both in zonal currents and western boundary currents, indicating that the global ocean overturning thermohaline circulation appears of multi-layer pattern.

SEASONAL VARIABILITY OF THE INDONESIAN THROUGHFLOW FROM A VARIABLE-GRID GLOBAL OCEAN MODEL

The objective of this study is to model the mean and seasonal mass transportof the Pacific to Indian O-cean throughflow using variable-grid global Ocean General CirculationModel (OGCM) with fine grid (1°/6) covering the area from 20°S to 60°N and from 98°E to 156°E.The computations show that Indonesian Throughflow (ITF) mass transport, computed as a sum ofthrough-strait transport, has maximum transport in Sept. (17. 5Sv) and minimum transport in Jan. (9.5Sv). The annual mean ITF transport amounts to 14. 5Sv. Twenty-two percent of this transport passesthrough Lombok Strait. Sixty-five percent of this transport passes through Timor Passage.Semi-annual variability is apparent in Lombok and Ombai Straits while annual variability is apparentin Timor Passage.

Impacts of climate change on hydrology,water quality and crop productivity in the Ohio-Tennessee River Basin

Nonpoint source pollution from agriculture is the main source of nitrogen and phosphorus in the stream systems of the Corn Belt region in the Midwestern US.The eastern part of this region is comprised of the Ohio-Tennessee River Basin(OTRB),which is considered a key contributing area for water pollution and the Northern Gulf of Mexico hypoxic zone.A point of crucial importance in this basin is therefore how intensive corn-based cropping systems for food and fuel production can be sustainable and coexist with a healthy water environment,not only under existing climate but also under climate change conditions in the future.To address this issue,a OTRB integrated modeling system has been built with a greatly refined 12-digit subbasin structure based on the Soil and Water Assessment Tool(SWAT)water quality model,which is capable of estimating landscape and in-stream water and pollutant yields in response to a wide array of alternative cropping and/or management strategies and climatic conditions.The effects of three agricultural management scenarios on crop production and pollutant loads exported from the crop land of the OTRB to streams and rivers were evaluated:(1)expansion of continuous corn across the entire basin,(2)adoption of no-till on all corn and soybean fields in the region,(3)implementation of a winter cover crop within the baseline rotations.The effects of each management scenario were evaluated both for current climate and projected mid-century(2046-2065)climates from seven global circulation models(GCMs).In both present and future climates each management scenario resulted in reduced erosion and nutrient loadings to surface water bodies compared to the baseline agricultural management,with cover crops causing the highest water pollution reduction.Corn and soybean yields in the region were negligibly influenced from the agricultural management scenarios.On the other hand,both water quality and crop yield numbers under climate change deviated considerably for all seven GCMs compared to the baseline climate.Future climates from all GCMs led to decreased corn and soybean yields by up to 20%on a mean annual basis,while water quality alterations were either positive or negative depending on the GCM.The study highlights the loss of productivity in the eastern Corn Belt under climate change,the need to consider a range of GCMs when assessing impacts of climate change,and the value of SWAT as a tool to analyze the effects of climate change on parameters of interest at the basin scale.