New normal? Historical context of recent global tropical cyclone inactivity Ryan N. Maue National Research Council AMS 30 th Conference on Hurricanes and.

New normal? Historical context of recent global tropical cyclone inactivity

Ryan N. MaueNational Research Council

AMS 30th Conference on Hurricanes and Tropical MeteorologyApril 16, 2012

2B.7

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?)

• Frequency Counts• Accumulated Cyclone

Energy (Bell et al. 2000)

• Only 34-knots + maximum one-minute sustained, tropical phase TCs

• Analogous to Power Dissipation Index (V 3 PDI, Emanuel 2005)

Knapp et al. (2010) BAMS

2max

410 vACE

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 near-record 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

TS | Hurr | Major Global: 75 | 39 | 21Northern Hemisphere: 54 | 27 | 16Southern Hemisphere: 18 | 9 | 3October 2011 - April 2012

Global Tropical Cyclone Frequency12-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]

Linear Trends

TS

Hurr

μ = 174 | 95

Global Tropical Cyclone Frequency24-month Running Sums TC (34 knots +) & HURR (64 knots +)

January 1, 2010 – December 31, 2011: 144 | 78

April 2010 – March 2012 = 140 TC | 77 HURR

Linear Trend

Global Tropical Cyclone Frequency12-month Running Sums HURR (64 knots +) & MAJOR HURR (96 knots +)

Global Tropical Cyclone ACE24-month Running Sums | January 1970 - March 2012

2max

410 vACE

Global

NH

[knots2]

Global Tropical Cyclone ACECalendar Sums: Global & Northern Hemisphere ++++ 1970 – 2011July-June offset yearly sums: Southern Hemisphere +++ 1971 - 2012

2max

410 vACE [knots2]

Historical global tropical cyclone landfalls: 1970-2010

Historical global tropical cyclone landfalls: 1970-2010

Weinkle et al. (in press, J Climate)

Relevant metric: global major hurricane landfall$…this subset of storms is a function of “climate”

Over 1970 to 2010 the globe averaged about 15 TC landfalls per yearOf 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 (2009-2011), 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

Historical global tropical cyclone landfallsWeinkle et al. (in press, J. Climate)

Moving forward into the 2020s… Frequency“Normal”ΔTC activity 2024 – 1970?

?

Moving forward into the 2020s… Integrated Metric (ACE)“Normal”ΔTC activity 2024 – 1970?

?

Moving forward into the 2020s…?

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?

Best metrics to measure TC climatology – what is normal?

Best metrics to measure climate change impacts on TCs?

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.

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.

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)

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 activityto anthropogenic influences.