Transcript Global Tropical Cyclone Database

2B.7
New normal? Historical context of recent global
tropical cyclone inactivity
Ryan N. Maue
National Research Council
AMS 30th Conference on Hurricanes and Tropical Meteorology
April 16, 2012
Thoughts
• What is normal for global tropical cyclone (TC)
activity?
• How do we quantify TC activity with our current
best-track [quality]? What’s our record book?
• For climatology (change), what is important? ratios,
counts, integrated metrics, SST impacts…etc.
• What are the relevant metrics ?
– Landfalls
Global Tropical Cyclone Database
• Best Track Data:
IBTrACS-All v03r03
includes global RSMCs +
other centers
• NHC HURDAT + JTWC
1981-2012 best tracks &
operational
• Pre-1981, combination of
available data, much less
reliable, e.g. UCAR ds824.1
(clear underestimate?)
Knapp et al. (2010) BAMS
• Frequency  Counts
• Accumulated Cyclone
Energy (Bell et al. 2000)
2
ACE  104 vmax
• Only 34-knots + maximum
one-minute sustained,
tropical phase TCs
• Analogous to Power Dissipation
Index (V 3 PDI, Emanuel 2005)
CONTINUED REANALYSIS
Historical Declines in TC Activity
Dramatic Downturns
• With many metrics, global
TC activity has decreased
markedly since 2006.
• Frequency and integrated
metrics such as ACE and
PDI have reached nearrecord lows (Maue, 2011)
• Has continued into 2012,
with no end in sight?
Recent Marks
• Calendar Year 2010 saw
69 TCs globally, fewest
since 1977. 75 in 2011.
• Northern Hemisphere in
2010 saw 46 TCs, fewest
since 1977.
• Global and Hemispheric
TC Accumulated Cyclone
Energy since 2007 has
plumbed record lows
2011 Global TC Activity: Frequency
Global:
Northern Hemisphere:
Southern Hemisphere:
October 2011 - April 2012
TS | Hurr | Major
75 | 39 | 21
54 | 27 | 16
18 | 9
| 3
Global Tropical Cyclone Frequency
12-month Running Sums TC (34 knots +) & HURR (64 knots +)
April 2011 – March 2012 = 74 TC | 38 HURR
Linear Trends
January 1, 2011 – December 31, 2011: 75 | 39
μ = 87 | 47
[66,107], [28,63]
Global Tropical Cyclone Frequency
24-month Running Sums TC (34 knots +) & HURR (64 knots +)
April 2010 – March 2012 = 140 TC | 77 HURR
TS
Hurr
Linear Trends
January 1, 2010 – December 31, 2011: 144 | 78
μ = 174 | 95
Global Tropical Cyclone Frequency
12-month Running Sums HURR (64 knots +) & MAJOR HURR (96 knots +)
Linear Trend
Global Tropical Cyclone ACE
24-month Running Sums | January 1970 - March 2012
Global
NH
2
ACE  104 vmax
[knots2]
Global Tropical Cyclone ACE
Calendar Sums: Global & Northern Hemisphere ++++ 1970 – 2011
July-June offset yearly sums: Southern Hemisphere +++ 1971 - 2012
2
ACE  104 vmax
[knots2]
Historical global tropical cyclone landfalls: 1970-2010
Historical global tropical cyclone landfalls: 1970-2010
Relevant metric: global major hurricane landfall$
…this subset of storms is a function of “climate”
Weinkle et al. (in press, J Climate)
Historical global tropical cyclone landfalls
Weinkle et al. (in press, J. Climate)
Over 1970 to 2010 the globe averaged about 15 TC landfalls per year
Of those 15, about 5 are intense (Category 3, 4 or 5)
1978 had the fewest with 7
2011 tied for second place for the fewest global landfalls with 10 (and 3
were intense, tying 1973, 1981 and 2002)
1999 had the most intense TC landfalls with 9
1981 had the fewest intense TC landfalls with zero
There have been only 8 intense TC landfalls globally since 2008 (20092011), very quiet but not unprecedented (two unique 3-year periods
saw only 7 intense landfalls)
The US is currently in the midst of a record streak without an intense
hurricane landfall (Wilma 2005)
http://rogerpielkejr.blogspot.com
Moving forward into the 2020s… Frequency
ΔTC activity 2024 – 1970?
“Normal”
?
Moving forward into the 2020s… Integrated Metric (ACE)
ΔTC activity 2024 – 1970?
“Normal”
?
Moving forward into the 2020s…
Best metrics to measure TC
climatology – what is normal?
?
Best metrics to measure climate
change impacts on TCs?
IPCC SREX (2012): “The present period of quiescence, as well as the period of
heightened activity leading up to the high point in 2005, does not clearly represent
substantial departures from past variability. (Maue, 2009)”
Global tropical cyclone frequency: annual mean ~ 87, range from 66-107.
Is the recent downturn a regional or global phenomena -- represent a climate shift
to a colder Pacific (-PDO)?
Active North Atlantic vs. inactive North Pacific. How long is this going to last?
Impacts on landfalls in the future?
IPCC, 2012: Managing the Risks of Extreme Events and Disasters to
Advance Climate Change Adaptation. A Special Report of Working
Groups I and II of the Intergovernmental Panel on Climate Change
(Field et al. 2012)
In summary, there is low confidence that any observed long-term (i.e., 40 years or
more) increases in tropical cyclone activity are robust, after accounting for past
changes in observing capabilities.
The uncertainties in the historical tropical cyclone records, the incomplete
understanding of the physical mechanisms linking tropical cyclone metrics to
climate change, and the degree of tropical cyclone variability provide only low
confidence for the attribution of any detectable changes in tropical cyclone activity
to anthropogenic influences.
There is low confidence in projections of changes in tropical cyclone genesis,
location, tracks, duration, or areas of impact. Based on the level of consistency
among models, and physical reasoning, it is likely that tropical cyclone related
rainfall rates will increase with greenhouse warming.
It is likely that the global frequency of tropical cyclones will either decrease or
remain essentially unchanged. An increase in mean tropical cyclone maximum
wind speed is likely, although increases may not occur in all tropical regions.