Abstract
This paper presents the applications of Fuzzy Rule Based Circulation Patterns (CPs) classification in the description and modelling of two different physical consequences of their form: Rainfall regimes and Wind generated Ocean Waves. The choice of the CP groupings is made by searching for those CPs which generate (i) different daily rainfall patterns over mesoscale regions and (ii) wave directions and heights at chosen shoreline locations. The method used to choose the groupings of CPs is a bottom-up methodology using simulated annealing, ensuring that the causative CPs are responsible for the character of the results. This approach is in marked distinction to the top-down approaches such as k-means clustering or Self Organising Maps (SOMS) to identify several classes of CPs and then finding the effects of those CPs on the variables of choice on given historical days. The CP groups we define are quite different for the two phenomena rainfall and waves, simply because different details of the pressure fields are responsible for wind and for precipitation. Large ocean waves are typically generated over fetches of the order of thousands of kilometres far off shore, whereas rainfall is generated by local atmospheric variables including temperature, humidity, wind speed and radiation over the area of concern. The spatial representativeness of the CPs is discussed and classifications obtained for different regions are compared. The paper gives examples of applications of the ideas over South Africa.
Highlights
IntroductionLocal weather (precipitation, temperature wind) and related phenomena such as floods, storm, and waves are strongly dependent on atmospheric processes
Local weather and related phenomena such as floods, storm, and waves are strongly dependent on atmospheric processes
To introduce the first experiment, which is to demonstrate the link between rainfall regimes and Circulation Patterns (CPs), we offer Figure 2, which shows the correspondence between (i) three CPs chosen from a set of 8 in Mpumalanga and (ii) the rainfall distribution at a particular rain-gauge in the region
Summary
Local weather (precipitation, temperature wind) and related phenomena such as floods, storm, and waves are strongly dependent on atmospheric processes. The patterns differ in their defining space Their link to local variables is determined after the classification and might for some variables yield a good distinction in the behavior while for others not. The second method acknowledges the fact that relatively small differences of the atmospheric variables might lead to very different behavior of the local variables This means that the classification should not intend to distinguish the patterns by producing very different CPs but to group CPs which to some extent are similar but explain the target variable as well as possible. While the classification of pressure fields on a purely statistical basis might reveal specific features of atmospheric dynamics, it might not provide the best basis for the explanation of the behavior of surface variables such as wind, temperature or precipitation. In this paper fuzzy rule based classifications are developed for precipitation and waves in South Africa
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