Tropical Cyclogenesis and Ecoinformatics Methods - New Ecoinformatics Tools in Environmental Science: Applications and Decision-making - page 609

Orleans, Louisiana, it reached category 5 on the morning of 28 August and then its
strength decreased slowly until 31 August. Hurricane Katrina passed New Orleans
on 29 August 2005 and by 31 August New Orleans was

flooded as result of
Hurricane Katrina. An analysis of meteorological data shows that the

fl

first signs of
the environmental instability began to originate on 20 August. Consequently, the
interval between 20 and 23 August can be considered as the uncertainty zone (see
Fig. 7.14 ). Thus, it is necessary to search the indicators of environmental instability
within this zone. Undoubtedly, the value of

2

ʔ , the width of zone N

2 , and the

2
2 depend on the hurricane category dynamics. Searching such
dependency is an important task.
Figure 7.15 represents a percolation cluster that was formed in the region of the
Bahamas in August of the 2005 hurricane season. The process of percolation cluster
formation shows that there exists a moment when the ocean-atmosphere system
changes its phase state. This moment is determined by the distances between

structure of zone N

ʻ and

* . Simulation of this process has shown that the moment at which this
transition occurs corresponds to the boundary between a storm and a hurricane of
the

* ,

ʻ ʼ and ʼ

first category. This is not a very acceptable result. Therefore, it is necessary to
introduce an additional indicator.
It can be seen that both percolation cluster sections have the zones of transition
to the in

nite cluster but are distinguished by the structural characteristics of the
percolation cluster. Section (x 2 , x 9 ) has the following parameters:

* = 0.2, * = 0.87

ʻ ʼ

* = 0.5, * = 0.94

and S=7.08. Section (x 10 , x 8 ) is characterized by the parameters ʻ ʼ

and S=22.5. The zone of the phase transition is de ned in each case by the

geometric reduction of the way between two zones of basic cluster each of which
satis es one state of the environment. It is evident that the moment of this reduction

Fig. 7.15 Principal scheme of the percolation transition in the OAS phase situations between
background and hurricane presence states during August/September 2005. Data used were from
the meteorological station No. SMKF1 (24 ° 37 ′ 36 ″ N, 81 ° 06 ′ 36 ″ W)