AtmosSci

發信人: Morbert.bbs@ptt.cc () 看板: AtmosSci
標 題: 澳洲颶風等級與Saffir/Simpson等級的比較
發信站: 批踢踢實業 (05/09/06 16:09:20 Tue)

********** EXTRA FEATURE **********

A COMPARISON BETWEEN THE AUSTRALIAN CYCLONE SEVERITY SCALE
AND THE SAFFIR/SIMPSON SCALE
----------------------------------------------------------

Both the U. S. National Weather Service and Australia's Bureau of
Meteorology (BoM) employ a 5-point scale by which to alert the public
of the general effects which can be expected from tropical cyclones of
varying intensities. In both systems tropical cyclones are classified
from Category 1 (the weakest) to Category 5 (the strongest), and each
scale seems to have been adopted enthusiastically by the general public
in both Australia and in the United States.

However, the scales are very different in their conception and in the
boundaries between their respective categories. The Saffir/Simpson
scale, used in the United States, is used for classifying tropical
cyclones which have reached hurricane intensity while the Australian
scale is utilized for all tropical cyclones of gale intensity or higher.
Nowadays, anyone anywhere in the world with internet access can follow
tropical cyclones in great detail, and there are many persons who delight
in tracking and discussing storms in all oceanic basins. Considerable
confusion has sometimes arisen when, for example, someone in the U. S.
is following an Australian cyclone and assuming that the category given
in the BoM warnings (and often aired in the international news media)
is equivalent to its Saffir/Simpson category.

The following chart summarizes the salient characteristics of the
two scales:

Characteristic Saffir/Simpson Australian
-------------------------------------------------------------------------
Beginning Point Hurricane force Gale force

Wind Parameter Sustained wind (1-min avg) Peak gusts

Wind Velocity Units Statute miles-per-hour Kilometres-per-hour


My purpose here is to provide information whereby persons interested
in comparing the two scales can easily do so. Table 1 defines the
Saffir/Simpson Scale in terms of the 1-min avg maximum sustained wind
(MSW) in statute miles-per-hour (mph) while Table 2 defines the
Australian Cyclone Severity Scale in terms of peak wind gusts in
kilometres-per-hour (km/hr). I have not included the narrative
describing the degree and type of damage which can be expected with
each category in both scales. Also, in both tables I have included
the qualifying wind velocity in nautical miles-per-hour (kts) along
with the nominal central pressure range in millibars (mb)--numerically
equal to hectopascals (hPa).


Table 1 - Saffir/Simpson Scale
==============================

Category 1-min avg MSW 1-min avg MSW Central Pressure
S/S (mph) (kts) (mb)
---------------------------------------------------------------------
1 74 - 95 64 - 82 >= 980
2 96 - 110 83 - 95 965 - 979
3 111 - 130 96 - 113 945 - 964
4 131 - 155 114 - 135 920 - 944
5 >= 156 >= 136

Table 2 - Australian Cyclone Severity Scale
===========================================

Category Peak gusts Peak gusts Central Pressure
Aust (km/hr) (kts) (hPa)
---------------------------------------------------------------------
1 90 - 124 49 - 67 986 - 995
2 125 - 169 68 - 91 971 - 985
3 170 - 224 92 - 121 956 - 970
4 225 - 279 122 - 150 930 - 955
5 >= 280 >= 151

The following two tables define each scale in terms of the other
scale's parameters, i.e., the Saffir/Simpson scale is defined in terms
of a 10-min avg MSW in kts, and peak gusts in kts and in km/hr (Table 3)
while the Australian scale is defined in terms of a 10-min avg MSW in
kts and a 1-min avg MSW in mph (Table 4).


Table 3 - Saffir/Simpson Scale in Terms of Australian Scale Parameters
======================================================================

Category 10-min avg MSW Peak Gusts Peak Gusts Equivalent
S/S (kts) (kts) (km/hr) Aust Category
-------------------------------------------------------------------------
1 56 - 72 79 - 101 146 - 190 mid-2 to mid-3
2 73 - 84 102 - 118 191 - 220 mid to high-3
3 85 - 99 119 - 140 221 - 260 high-3 to mid-4
4 100 - 118 141 - 166 261 - 310 mid-4 to mid-5
5 >= 119 >= 167 >= 311 mid to high-5


Table 4 - Australian Scale in Terms of Saffir/Simpson Scale Parameters
======================================================================

Category 10-min avg MSW 1-min avg MSW 1-min avg MSW Equivalent
Aust (kts) (kts) (mph) S/S Category
-------------------------------------------------------------------------
1 34 - 47 38 - 54 44 - 62 none
2 48 - 64 55 - 73 63 - 84 none to mid-1
3 65 - 85 74 - 96 85 - 111 mid-1 to high-2
4 86 - 106 97 - 120 112 - 139 low-3 to low-4
5 >= 107 >= 120 >= 140 mid-4 and up


Finally, as an additional aid to comparison, I have included a
table (Table 5) comparing each cyclone scale with the Dvorak scale,
used extensively in estimating tropical cyclone intensity from visible
and infrared satellite imagery. I have started the table with T2.0
since neither TPC/NHC nor the BoM TCWCs routinely issue advisories/
advices/warnings for systems less than that Dvorak rating. (See the
key following the table for an explanation of the abbreviations used.)


Table 5 - Comparison of Dvorak Scale with Cyclone Scales
========================================================

Dvorak MSW MSW TPC/NHC Australian
T-Number (1-min kts) (10-min kts) Category Category
-------------------------------------------------------------------
T2.0 30 26 TD TL
...................................................................
T2.5 35 31 TS TL
...................................................................
T3.0 45 40 TS TC-1
...................................................................
T3.5 55 48 TS TC-2
...................................................................
T4.0 65 57 H-1 TC-2
...................................................................
T4.5 77 68 H-1 TC-3
...................................................................
T5.0 90 79 H-2 TC-3
...................................................................
T5.5 102 90 H-3 TC-4
...................................................................
T6.0 115 101 H-4 TC-4
...................................................................
T6.5 127 112 H-4 TC-5
...................................................................
T7.0 140 123 H-5 TC-5
...................................................................
T7.5 155 136 H-5 TC-5
...................................................................
T8.0 170 150 H-5 TC-5
-------------------------------------------------------------------

Key to Abbreviations:
---------------------
TD tropical depression
TL tropical LOW
H-n hurricane of Saffir/Simpson category "n"
TC-n tropical cyclone of category "n" on Australian scale


Most of the information presented above was obtained from the
websites of Australia's Bureau of Meteorology and the Tropical
Prediction Center/National Hurricane Center. A special thanks to
Michael Bath for providing information regarding the nominal central
pressures corresponding to the Australian scale categories as well
as making some suggestions concerning formatting and presentation
of the tables.


http://www.typhoon2000.ph/garyp_mgtcs/feb06sum.htm

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