Presentation on theme: "National Research Council"— Presentation transcript:
1 National Research Council 2B.7New normal? Historical context of recent global tropical cyclone inactivityRyan N. MaueNational Research CouncilAMS 30th Conference on Hurricanes and Tropical MeteorologyApril 16, 2012
2 What is normal for global tropical cyclone (TC) activity? ThoughtsWhat 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 ?LandfallsNormal: mean or seasonal, stratified by ENSO phase, counts or some other metric.Measure TC activity: size, atm/ocean impact (SST imprint, wake), landfall or not, counts or ACE or PDI.Is our record book sufficient – back to when – basin dependent?Climatology: longer time series, integrated values vs. point valuesTo understand changes in TC activity, we need numerator and denominator of our metrics.Many customers of TC climatology data. Climate change due to AGW very important for policy.
3 Global Tropical Cyclone Database Best Track Data:IBTrACS-All v03r03 includes global RSMCs + other centersNHC HURDAT + JTWC best tracks & operationalPre-1981, combination of available data, much less reliable, e.g. UCAR ds824.1(clear underestimate?)Frequency CountsAccumulated Cyclone Energy (Bell et al. 2000)Only 34-knots + maximum one-minute sustained, tropical phase TCsAnalogous to Power Dissipation Index (V 3 PDI, Emanuel 2005)RecipeUsage of different datasets with discontinuous available data is subjective.There are many datapoints prior to the 1970s that are just plain missing or simply TD, TS, H intensity without values, clear underestimate.Not always information about the tropical or extratropical phase, may be pretty important for WPAC and NATL when long-track recurvers are present.CONTINUED REANALYSISKnapp et al. (2010) BAMS
4 Historical Declines in TC Activity Dramatic DownturnsRecent MarksWith 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?Calendar Year 2010 saw 69 TCs globally, fewest since in 2011.Northern Hemisphere in 2010 saw 46 TCs, fewest since 1977.Global and Hemispheric TC Accumulated Cyclone Energy since 2007 has plumbed record lowsJust numbers or trivia without context.
5 2011 Global TC Activity: Frequency TS | Hurr | MajorGlobal: | | 21Northern Hemisphere: | | 16Southern Hemisphere: | | 3October April 2012
6 Global Tropical Cyclone Frequency 12-month Running Sums TC (34 knots +) & HURR (64 knots +)April 2011 – March 2012 = 74 TC | 38 HURRObviously the top line is the most sensitive to increased observation network density.January 1, 2011 – December 31, 2011: 75 | 39μ = 87 | 47Linear Trends[66,107], [28,63]
8 Global Tropical Cyclone Frequency 12-month Running Sums HURR (64 knots +) & MAJOR HURR (96 knots +)Linear Trend
9 24-month Running Sums | January 1970 - March 2012 [knots2]Global Tropical Cyclone ACE24-month Running Sums | January March 2012GlobalNH
10 Global Tropical Cyclone ACE [knots2]Calendar Sums: Global & Northern Hemisphere – 2011July-June offset yearly sums: Southern Hemisphere
11 Historical global tropical cyclone landfalls: 1970-2010 Good data for the Atlantic but who knows about elsewhere.
12 Historical global tropical cyclone landfalls: 1970-2010
13 Relevant metric: global major hurricane landfall$ …this subset of storms is a function of “climate”Weinkle et al. (in press, J Climate)
14 Historical global tropical cyclone landfalls Weinkle et al. (in press, J. 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 72011 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 91981 had the fewest intense TC landfalls with zeroThere have been only 8 intense TC landfalls globally since 2008 ( ), 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)
15 ? ΔTC activity 2024 – 1970? “Normal” Moving forward into the 2020s… FrequencyΔTC activity 2024 – 1970?“Normal”?Campaign slogan in Romney’s reelection slogan, or Hillary’s battle cry.
16 ? ΔTC activity 2024 – 1970? “Normal” Moving forward into the 2020s… Integrated Metric (ACE)ΔTC activity 2024 – 1970?“Normal”Campaign slogan in 2016.?
17 ? 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 fromIs 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?
18 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 activityto 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.
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