Objective analysis of climatological fields: results of test analyses using a successive correction method

• Main Author: Josey, S.A.
• Format: Report
• Language: English
• Published: Southampton Oceanography Centre 1996
• Subjects: North Atlantic
• Online Access: http://nora.nerc.ac.uk/id/eprint/502877/; https://nora.nerc.ac.uk/id/eprint/502877/1/mtd96_21.pdf

The use of objective analysis techniques in climatological studies is reviewed and the properties of a widely used scheme, namely a successive correction method (SCM), are described in detail. A sensitivity study of an SCM with a Gaussian weight function is carried out using raw 1 o x 1 o monthly mean global evaporation rates from the UWM/COADS atlas to provide the observation field. The results are used to suggest a set of parameters for the analysis of climatological fields which are being generated from ship meteorological reports in the COADS 1 a dataset. The analysed fields are found to be most sensitive to the value of the influence radius on the last pass of the analysis, with the choice of background field and number passes being of only secondary importance. A minimum value for the influence radius in the range 21 0 - 350 km, which is somewhat smaller than that used in several past analyses, is found to be appropriate in regions of high data density such as the North Atlantic The possibility of reducing the amount of noise in the analysed field by imposing a threshold on the number of observations required to generate a mean is investigated but is found to be impractical at a grid scale of 1 degree x 1 degree as too much information is lost from the observation field. Finally, the integrated characteristics of the analysed field are found to be insensitive to the level of interpolation in the SCM which suggests that this is not an important factor in the context of heat budget calculations.