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The Earth’s Atmospheric Angular Momentum Budget and its Representation in Reanalysis Observation Datasets and Climate Models

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Name

The Earth’s Atmospheric Angular Momentum Budget and its Representation in Reanalysis Observation Datasets and Climate Models 

 

Author

Simon Driscoll

 

Publication Date

August 2010

 

Abstract

Angular Momentum is a fundamental quantity in any rotating system. In this disser- ation we are predominantly concerned with the theory of conservation of angular momen- tum in the Earth’s Atmosphere, and whether this theory is represented in the National Oceanic and Atmospheric Administration’s (NOAA’s) Twentieth Century Reanalysis Ver- sion 2 Observation Dataset, the Hadley Centre’s HadCM3 and HadGEM1 climate models, and the NOAA’s GFDL CM2.0 climate model. By doing this we gain useful information as to whether the reanalysis observation dataset has internally consistent physics after the data assimilation process and the parameterization of variables, and we can also gain use- ful information as to whether a climate model (that does not require the data assimilation phase) has correct parametrizations of variables and internally consistent physics. 

 

We find that the NOAA Reanalysis Observation Dataset does not conserve angular momentum, and that the torques are the major source of error. There is error in all torques, especially during the northern hemisphere winter. The little change in the latitudinal torque profiles for the reanalysis observation dataset, calculated for 1890-1899 and 1990- 1999, suggests that with the aid of the reanalysis process a very poor observation network can give the same latitudinal torque profiles as the observation network of today. 

 

It is also found that the HadCM3 model has a serious error in its representation of the mountain torque, and we note with great interest that the climate model HadGEM1 (who’s physical processes were developed from HadCM3) has significantly smaller values in its regional friction torque than that of HadCM3. Indeed all the other latitudinal profiles calculated in this dissertation, implying the surface winds are too weak, and even suggest- ing there may be differences in the whole circulation between HadGEM1 and HadCM3. We also find error in the spatial patterns of the torques of the NOAA GFDL CM2.0 model whose near symmetric torques imply that the circulation throughout the atmosphere is likely to be symmetric about the equator, thus the northern hemisphere circulation is the same as that of the southern hemisphere in the model. 

 

Link to original paper

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.225.904&rep=rep1&type=pdf

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