A careful study on the integral properties of the primitive hydrostatic balance equations for baroclinic atmosphere is carried out, and a new scheme todesign the global adiabatic model of atmospheric dynamics ispresented. This scheme includes a method of weighted equal-areamesh and a fully discrete finite difference method with quadraticand linear conservations for solving the primitive equationsystem. Using this scheme, we established a new dynamical corewith adjustable high resolution acceptable to the availablecomputer capability, which can be very stable without anyfiltering and smoothing. Especially, some important integralproperties are kept unchanged, such as the anti-symmetries of thehorizontal advection operators and the vertical convectionoperator, the mass conservation, the effective energy conservationunder the standard stratification approximation, and so on. Somenumerical tests on the new dynamical core, respectively regardingits global conservations and its integrated performances inclimatic modeling, incorporated with the physical packagesfrom the Community Atmospheric Model Version 2 (CAM2) of NationalCenter for Atmospheric Research (NCAR), are included.
WANG Bin, WAN Hui, Jl Zhongzhen, ZHANG Xin, YU Rucong, YU Yongqiang & LIU HongtaoState Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
Response of the Atlantic thermohaline circula- tion (THC) to global warming is examined by using the cli- mate system model developed at IAP/LASG. The evidence indicates that the gradually warming climate associated with the increased atmospheric carbon dioxide leads to a warmer and fresher sea surface water at the high latitudes of the North Atlantic Ocean, which prevents the down-welling of the surface water. The succedent reduction of the pole-to- equator meridional potential density gradient finally results in the decrease of the THC in intensity. When the atmos- pheric carbon dioxide is doubled, the maximum value of the Atlantic THC decreases approximately by 8%. The associ- ated poleward oceanic heat transport also becomes weaker. This kind of THC weakening centralizes mainly in the northern part of the North Atlantic basin, indicating briefly a local scale adjustment rather than a loop oscillation with the whole Atlantic “conveyor belt” decelerating.
Due to the decrease in grid size associated with the convergence of meridians toward the poles inspherical coordinates, the time steps in many global climate models with finite-difference method are restrictedto be unpleasantly small. To overcome the problem, a reduced grid is introduced to LASG/IAP world oceangeneral circulation models. The reduced grid is implemented successfully in the coarser resolutions versionmodel L30T63 at first. Then, it is carried out in the improved version model LICOM with finer resolutions. Inthe experiment with model L30T63, under time step unchanged though, execution time per single model run isshortened significantly owing to the decrease of grid number and filtering execution in high latitudes. Resultsfrom additional experiments with L30T63 show that the time step of integration can be quadrupled at most inreduced grid with refinement ratio 3. In the experiment with model LICOM and with the model’s original timestep unchanged, the model covered area is extended to the whole globe from its original case with the grid pointof North Pole considered as an isolated island and the results of experiment are shown to be acceptable.
