Mean and Eddy Transports of Angular Momentum, Water Vapor, and Energy in the Global Atmosphere

Abstract

 Real global data of seven levels (surface pressure, geopotential heights for 700, 500, 300, 200, 100, and 70 mb) analyzed by Baumhefner for the period of 15-19 J anuary 1958 (IGY) are used to evaluate the transports of angular momentum, water vapor, and energy due to mean meridional circulation and eddy motions. Since only mass fields are analyzed, a technique is used to claim the fields of wind and water vapor. With the aid of a six-layer general circulation model developed at the National 'Center for Atmospheric Research (NCAR), short-range forecasts are made from analyzed initial mass fields with geostrophic wind as an initial condition. A climatological zonal mean specific humidity distribution for January is assumed as the initial field for water vapor. It is found that the wind and water vapor fields evolving after 24 hours of time integration appear to be usable for the evaluation of various transport quantities.
 The computed mean and eddy transports of momentum, water vapor, and energy are compared with those of various observational sources and of a simulated January starting from an isothermal atmosphere with the NCAR general circulation model. It is shown that the values of various transport quantities for the January 1958 case in the Northern Hemisphere are in reasonable agreement with those of other sources. However, the values of transport quantities in the Southern Hemisphere are underestimated due to weak wave activity. The weakness of eddy motions in the Southern Hemisphere is presumably attributed to difficulty in the initial data analysis owing to sparsity of observation stations in the Southern Hemisphere.
 In this study, we intend to demonstrate that the diagnostic analyses of the mean and eddy transports of various meteorological quantities can be performed from basic data sets with the use of a general circulation model as the means of imposing dynamical constraints among meteorological variables.