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Accumulated Cyclone Energy worldwide


Accumulated Cyclone Energy worldwide23-12-2012 23:41
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Accumulated Cyclone Energy worldwide

Based on data from Maue, RN (2011), I have studied the development of Accumulated Cyclone Energy (ACE) in the years January 1970 - September 2012 by oceans. This is a purely descriptive analysis to be seen as complementary to what can be found at PoliClimate . Data is available here Accumulated Cyclone Energy data .
Data exists from the following oceans:

The Atlantic Sea (Atl)
The Eastern Pacific (Epac)
The Western Pacific (Wpac)
The Indian Ocean (Io)
The Southern Hemisphere (SH)

This post is an attempt to provide an overview and a call for climate experts to prepare more comprehensive posts about tropical cyclones and not just for the Atlantic Sea.

Due to the American news media dominated position, we hear a lot about what is happening in the Atlantic Sea in respect of tropical cyclones. This is not proportional to the share of tropical cyclones in the Atlantic Sea compared to the total number of tropical cyclones worldwide.

Bjørn Lomborg has recently, i.e. 30 October 2012, used a low value of ACE, as an argument against global Al Gore and hurricane Sandy.


Bjørn Lomborg:
There are no reasons to believe that Hurricane Sandy would be caused by global warming. It's a hurricane of relatively low strength - it is unusual jet stream, but this one was also in 1953. After Katrina in 2005 talked Al Gore much about that we would get much worse hurricanes, and since then the global hurricane index dropped to the lowest since 1970.

I do not claim that I have found the whole truth and got everything right in this post, because there are a number of other issues that should be addressed, namely the link to ocean temperature in the areas that are vulnerable to tropical cyclones and link to AMO /PDO.

On this background I hope experts in tropical cyclones will be helpful in providing better information about tropical cyclone and Accumulated Cyclone Energy to the readers of this blog than I can provide here and now.

Summary
1) There is no evidence of a systematic increasing or decreasing trend in ACE for the years 1970-2012.

2) There is a cyclical variation in the ACE of 6 and 12 months' length

3) The contribution of ACE from the Eastern and Western Pacific is approx. 56% of the total ACE

4) The contribution of ACE from the Atlantic Sea is approx. 13% of the total ACE

5) The minimum and maximum values of ACE per month are respectively 1.8 and 266.4

6) The average value of ACE per month is 61.2

7) The minimum and maximum values of ACE per year are respectively 416.2 and 1145.0

8) The average value of the ACE per year is 730.5

9) The total of ACE for 2012 through September is 540.8.

10) There is a correlation of ACE between some oceans



Overview
The following graph shows the development of ACE by oceans. The figures are stacked on top of each other. This means: the lower curve shows the Atlantic Sea. The next graph shows the sum of ACE from the Atlantic Sea and from the Indian Ocean, etc.



These curves show that there is a minimum in late 1970'Th, a maximum in early 1990'Th and another minimum around 2011. There is a considerable random variation in the ACE and therefor it is difficult to judge any trends.

We know that the Major Hurricanes have the largest contribution to ACE - approx. 60% - and since we know that their number is increasing because of increasing sea surface temperatures, an increase in the ACE is expected. This is a paradox.

If sea surface temperature by month for all tropical cyclone prone area were available, it will be interesting to investigate relations between ACE and sea surface temperature. Analysis of relations to AMO and PDO is also of interest.


The maximum / minimum value of ACE is observed in May 2012/September 2004 to be respectively 1.8 and 266.4.

The distribution of ACE by ocean appears in the following graph:

It is clear from this graph that the largest contribution to the total ACE comes from the Western Pacific. For all years the total ACE for the Atlantic Sea, Eastern Pacific, the Western Pacific, The Indian Ocean and The Southern Hemisphere makes up 13%, 17%, 39%, 2% and 29% respectively. It looks like The Atlantic Sea has an increasing share of ACE.

The news media are focused on what is happening in the Atlantic Sea, despite the fact that the area represents only 13% of the total ACE.

The histograms of ACE per month and per year are presented in the following graph:

While the histogram of the monthly ACE is clearly skewed to the right, this is not the case for the annual ACE.

Cyclic variation
There is a clear cyclic variation within a single year in the total ACE. This is shown in the following four graphs:

The top left graph shows the raw data with fitted curve i.e. a Lowess curve. The distribution of the points shows that ACE has a right-skewed distribution, i.e. many small values of ACE and fewer very large values. Use the zoom to see details.

The top right graph shows the spectrogram of ACE for the years 1970-2012. There are two distinct peaks corresponding to two cyclic signals of 6 and 12 months. This is expected due to the seasonal variations in the Northern and Southern Hemispheres respectively.

The lower left graph displays the observations with a fitted curve consisting of the sum of two harmonic oscillations with periods 6 and 12 months, but only for the years 2005-2012. The fitted curve can only explain approx. 55% of the variations in the ACE. There is no linear trend. This means that the level of ACE is constant over the entire period. There is, therefore, a conflict between the visual impressions of the evolution of ACE from the very first graph in this analysis.

The bottom right graph shows the standardized residuals. In total there are 513 observations, of which 27 observations are outside the range [-1.96, 1.96], where 5 % is expected and 5.3 % is observed. The present model does not fully cope with the fluctuations in mid-1990 and mid-2000.

A possible conclusion is that there has not been observed a global warming signal in the development of ACE during the years 1970-2012, since the global temperature has increased over the same years.
This is expected according to the IPCC.

Correlations
It is obviously of interest to investigate whether there are any correlations of ACE between oceans. This is done in summary form in the following graph:

In the above graph there are 25 panels in 5 rows and 5 columns. The name of the ocean is shown in the diagonal. The naming of the cells given by (1,1), (1,2). ..:

Atlantic Sea and Eastern Pacific
There has been a significant negative correlation of -0.38. This is shown on the panel (1,2) and the graph of the panel (2,1). This means that if there is a large positive deviation in ACE in the Atlantic Sea, a large negative deviation is expected in the Eastern Pacific and vice versa. In this way, the tropical cyclone in the Atlantic Sea and in the Eastern Pacific is a seesaw.


The Western Pacific and Eastern Pacific
There has been a significant positive correlation of 0.37. This is shown on the panel (2,3) and the graph of the panel (3,2). This means that if there is a large positive deviation of ACE in the Eastern Pacific, a large positive deviation is expected in the Eastern Pacific. The tropical cyclone in the The Western Pacific and Eastern Pacific are cooperating. Both are up and down at the same time.

The Western Pacific and the Southern Hemisphere
There has been a significant positive correlation of 0.41. This is shown on the panel (3,5) and the graph of the panel (5,3). This means that if there is a large positive deviation of ACE in the Western Pacific, a large positive deviation is expected in the Southern Ocean. The tropical cyclone in The Western Pacific and the Southern Hemisphere are cooperating. Both are up and down at the same time.

There have been no other correlations than those described above.

It seems a little surprising that there is a negative correlation between ACE in the Atlantic Sea and Eastern Pacific. The other correlations are expected as a result of neighboring oceans.

I would be pleased if some could guide me to monthly average temperature for each hurricane prone area of the various ocean.


This post is written with the right to be updated if errors and misunderstanding are discovered or new knowledge emerges.

Links:
Climate Variability and Change: Impacts on Atlantic Hurricanes
KNMI Climate Explorer
Join the debate Accumulated Cyclone Energy worldwide:

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