Objektive Analyse aktueller Wind- und Druckfelder über dem Nordatlantik.

Ennenga, Ulla (1985) Objektive Analyse aktueller Wind- und Druckfelder über dem Nordatlantik. (Doctoral thesis/PhD), Christian-Albrechts-Universität Kiel, Kiel, Germany, 103 pp.

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Abstract

For oceanographic purposes the knowledge of the wind field at the sea surface is very important. Due to the smaller scales of the oceanic circulations, high resolution is required. Since synoptic observations at sea are comparatively sparse, optimum use cf the available information is desired. The paper describes a method, where the wind and pressure data from synoptic surface ship observations are simultaneously analysed. The method uses a second order polynominal in surface pressure, and relates surface wind speed and direction to pressure gradient by empirical
relationships. In this way wind and pressure observations are fitted simultaneously, using a least squares fit to obtain local optimal estimates of pressure gradients and therefrom surface wind fields.
By combined analysis of wind and pressure data, more information is available to eliminate erroneous data. Because of the irregular and highly variable distribution of synoptic reports, there are frequently areas with few observations. Together with the polynominal fit, a field of error estimates is provided.
The different observations (pressure, wind speed, direction) have different observational errors. Also, they respond to a different
degree to subgrid scale processes. Hence, with the least squares fit, a weighting is introduced, which allows to give more emphasis to pressure or wind informations. lt is often believed that the pressure field may be better interpolated and provides much more information than the wind field. The results show: combination of wind and pressure fields yields a better description than the use of wind or pressure data alone. Note that it is not the pressure itself, but the pressure gradient that matters. The unevitable smoothing eliminiates extrems when pressure data alone are used.
The method has been applied to observations from the North Atlantic Ocean. An effort has been made to verify the analysis in a statistical sense by independent data. lt shows that for the
data density typical of the North Atlantic, a second order polynominal in pressure is superior to a first order fit.
The relationship between pressure and wind field was used in two forms: independent of stability and with stability determined from mean air sea temperature difference. Though the routine ship
observations of air sea difference show a large scatter the results indicate that consideration of stability provides for a better description of the wind field.

Document Type: Thesis (Doctoral thesis/PhD)
Thesis Advisors: Hasse, Lutz
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-ME Maritime Meteorology
Date Deposited: 21 Mar 2018 09:11
Last Modified: 21 Mar 2018 09:11
URI: http://oceanrep.geomar.de/id/eprint/42314

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