1. TC’s role in climate The bigger question: How would the climate be different if TCs were not “permitted” to form?

2. Energy transport http://www.onr.navy.mil/focus/ocean/motion/currents1.htm http://www.crh.noaa.gov/mqt/webpics/weatherpics/Big/thunderstorm%201.jpg

3. Relative Roles Newton (1972) Later revised by Trenberth et al. Latent heat Atmosphere Ocean Total

4. Defining the TC role in climate: TCs play a role in the energy transport, but the magnitude and nature varies considerably on a case by case basis TCs play a role in the energy transport, but the magnitude and nature varies considerably on a case by case basis In the deep tropics TCs greatly warm the atmosphere, but do not significantly cool the ocean. Non-recurving TCs act to pump up the tropical atmosphere:Increase T EQ -T Pole In the deep tropics TCs greatly warm the atmosphere, but do not significantly cool the ocean. Non-recurving TCs act to pump up the tropical atmosphere:Increase T EQ -T Pole Recurving TCs cool the subtropical waters, and warm/moisten the midlatitude/polar atmosphere: Decrease T EQ -T Pole Recurving TCs cool the subtropical waters, and warm/moisten the midlatitude/polar atmosphere: Decrease T EQ -T Pole Do not necessarily remove the instability that created them Do not necessarily remove the instability that created them

5. One component of the TC role http://svs.gsfc.nasa.gov/vis/a000000/a001000/a001066/ How long does it take for the upwelling- induced cooling to return (warm) to climatology? How long does it take for the upwelling- induced cooling to return (warm) to climatology? What is the “atmospheric and/or oceanic” memory of a TC’s passage? What is the “atmospheric and/or oceanic” memory of a TC’s passage?

8. Oceanic+Atmospheric Memory of TCs

9. TC-induced oceanic cooling The time period for the MPI to return to climatology after a TC passes: The time period for the MPI to return to climatology after a TC passes: 60 days (Category 3,4,5 TC) 60 days (Category 3,4,5 TC) 40 days (Category 1,2 TC) 40 days (Category 1,2 TC) 30 days (Tropical storm) 30 days (Tropical storm) This MPI restoration to climatology is performed by: This MPI restoration to climatology is performed by: Enhanced surface fluxes Enhanced surface fluxes Enhanced solar radiation Enhanced solar radiation Calendar catching up Calendar catching up Aggregate impact is largest for above normal frequency of recurving TCs Aggregate impact is largest for above normal frequency of recurving TCs Hart, Watson, Maue (MWR 2007) Hart, Watson, Maue (MWR 2007) http://svs.gsfc.nasa.gov/vis/a000000/a001000/a001066/

10. By basin

11. Atmospheric memory

12. Zoom in on atmosphere memory

13. Another component of the TC role TC-induced atmospheric warming

14. Hypothesis In autumns when the recurving tropical cyclone activity is enhanced, TCs have contributed more than normal toward the heat redistribution In autumns when the recurving tropical cyclone activity is enhanced, TCs have contributed more than normal toward the heat redistribution In these years, the subsequent role of meridional temperature flux by other methods might be suppressed since the midlatitudes/poles are warmer than normal (less work to be done) In these years, the subsequent role of meridional temperature flux by other methods might be suppressed since the midlatitudes/poles are warmer than normal (less work to be done)

15. Data & Definitions Northern hemisphere (NH) best-track tropical cyclone record for 1955-2005: Northern hemisphere (NH) best-track tropical cyclone record for 1955-2005: North Atlantic + Eastern Pacific + Western Pacific + North Indian Basins North Atlantic + Eastern Pacific + Western Pacific + North Indian Basins Subsequent JFM means from: Subsequent JFM means from: NCEP/NCAR reanalysis (1955-2005; 1979-2005) NCEP/NCAR reanalysis (1955-2005; 1979-2005) ECMWF ERA40 reanalysis (1957-2002) ECMWF ERA40 reanalysis (1957-2002) Recurving TC: Recurving TC: A TC that forms equatorward of 30  N and reaches a latitude of at least 40  N prior to dissipation A TC that forms equatorward of 30  N and reaches a latitude of at least 40  N prior to dissipation These TCs are argued to have contributed most significantly to weakening the pole-to-equator  T These TCs are argued to have contributed most significantly to weakening the pole-to-equator  T

16. Full disclosure…keep in mind we are ignoring: Whether the historical record truncated the track Whether the historical record truncated the track The evolving quality of the historical record The evolving quality of the historical record When (month) the TC recurves When (month) the TC recurves Where the TC recurves Where the TC recurves How intense the TC is when it recurves How intense the TC is when it recurves The role of Atlantic vs. Pacific recurvers The role of Atlantic vs. Pacific recurvers Larger scale impacts, such as volcanic eruptions, that may mask the recurving TC impact Larger scale impacts, such as volcanic eruptions, that may mask the recurving TC impact Long-term changes in climate Long-term changes in climate Thus – this is not close to an optimized study of the topic Thus – this is not close to an optimized study of the topic

17. Results: Recurving Climo “Inactive” years “Inactive” years 1956, 1968, 1970, 1971, 1977, 1979, 1982, 1983, 1984, 1986, 1987, 1988, 1991, 2002 1956, 1968, 1970, 1971, 1977, 1979, 1982, 1983, 1984, 1986, 1987, 1988, 1991, 2002 Mean year: 1980.3 Mean year: 1980.3 Mean MEI: 0.50 (Neutral) Mean MEI: 0.50 (Neutral) “Active” years “Active” years 1955, 1959, 1962, 1972, 1975, 1976, 1989, 1993, 1994, 1995, 1996, 1997, 1998, 2001, 2005 1955, 1959, 1962, 1972, 1975, 1976, 1989, 1993, 1994, 1995, 1996, 1997, 1998, 2001, 2005 Mean year: 1984.5 Mean year: 1984.5 Mean MEI: 0.12 (Neutral) Mean MEI: 0.12 (Neutral)

18. Results: Recurving Climo Western north Pacific Eastern north Pacific North Atlantic “Active” recurving TC years “Normal” recurving TC years “Inactive” recurving TC years

19. Results: 51-year (1955-2005) recurving climatology Mean number of NH recurving TCs is 9 Mean number of NH recurving TCs is 9 Q1: 5 “inactive” recurving year threshold Q1: 5 “inactive” recurving year threshold Q3: 12 “active” recurving year threshold Q3: 12 “active” recurving year threshold Surprisingly stable measure of extremes: Surprisingly stable measure of extremes: 1948-2005:Q1: 6, Q3: 12 1948-2005:Q1: 6, Q3: 12 1955-2005:Q1: 5, Q3: 12 1955-2005:Q1: 5, Q3: 12 1979-2005:Q1: 5, Q3: 12 1979-2005:Q1: 5, Q3: 12 Range: 2-19 [hence, wildcard….] Range: 2-19 [hence, wildcard….]

20. Example Years: 1996 vs. 1977 Images courtesy of Unisys 19 “Recurving” storms vs. 4 “recurving” storms

21. Results: 500mb total meridional temperature flux in winter following TC season

22. JFM Winter following recurving TC season Total 500mb temperature flux (NCEP/NCAR reanalysis)

23. Results 5-10% midlatitude 500mb JFM temp. flux difference between: 5-10% midlatitude 500mb JFM temp. flux difference between: 5 recurving TCs and 12 recurving TCs 5 recurving TCs and 12 recurving TCs An average of 0.5-2% JFM midlatitude 500mb temp. flux reduction per TC, depending on reanalysis dataset An average of 0.5-2% JFM midlatitude 500mb temp. flux reduction per TC, depending on reanalysis dataset Next, examine stationary eddies only Next, examine stationary eddies only

24. Stationary Eddies Only [Long-term mean winter long-wave pattern] Following inactive recurving season Following active recurving season

25. Robustness / Significance: Stationary Eddies only Following inactive recurving season Following active recurving season

26. Winter thickness following anomalous recurving TCs

27. Winter temperature response to recurving TC activity

28. Winter precipitation response to recurving TC activity

29. Jet Location / Strength & Hadley/Ferrell/Polar Cell Modulation Polar Jet deceleration and Rossby wave number shift? Subtropical Jet acceleration Hadley Cell and Walker Circulation acceleration? Why the lack of symmetry between top and bottom panels?

30. How does this anomalous temperature patter vary in the vertical?

31. Jan. temp. anomaly after TC season Five or less recurving TCs Twelve or more recurving TCs Increased N Increased  T Decreased N Decreased  T TC-related (?) modified baroclinity and static stability => Shift in winter extratropical cyclone distribution

32. The paradox The warm anomaly of a TC cools rapidly as it reaches the higher lats. (emission as T 4 ) The warm anomaly of a TC cools rapidly as it reaches the higher lats. (emission as T 4 ) So, how does the impact of a recurving TC extend into the weeks to months to the winter season? So, how does the impact of a recurving TC extend into the weeks to months to the winter season? First: The deep tropics are largely a reservoir of heat, and thus warming of the higher latitudes is not balanced by deep tropical cooling [  net hemispheric warming] First: The deep tropics are largely a reservoir of heat, and thus warming of the higher latitudes is not balanced by deep tropical cooling [  net hemispheric warming] Second: Nonlinear impacts - snowcover changes Second: Nonlinear impacts - snowcover changes

33. One method for nonlinear extension of TC impact? TC-induced snowcover anomalies that lead to albedo changes up to the start of winter? 3 days after TC 7 days 14 days 30 days 45 days 60 days ERA40 snowcover anomaly following TC recurvature: 75 storm composite in October

34. What about a bigger forcing? It is possible there is something bigger, larger, that is forcing EVERYTHING It is possible there is something bigger, larger, that is forcing EVERYTHING TC recurvature could be a tracer for this bigger forcing mechanism TC recurvature could be a tracer for this bigger forcing mechanism Maybe there is anomalous climate in the spring/summer/fall that is manipulating both the TC recurvature and the subsequent winter! Maybe there is anomalous climate in the spring/summer/fall that is manipulating both the TC recurvature and the subsequent winter! Prior autumn, Global warming, PNA, NAO, AO, etc Prior autumn, Global warming, PNA, NAO, AO, etc

35. Is this recurving TC activity a response to baroclinic activity of prior autumn? No!!!!

36. Impact of Global warming? Median years: Small recurving dataset: 1982 Large recurving dataset: 1989 Can the median year difference be driving the entire flux difference? In such a case, the small recurving dataset should have STRONGER mean winter flux than the large recurving!! We see the opposite!

37. Impact of global warming? If the long-term climate change were dictating the winter impact following TC recurvature, we would be seeing the OPPOSITE pattern to what we have found. This only increases the statistical significance of the results!

38. Teleconnection masterminding? Removing anomalous AO years Removing anomalous ENSO years Removing anomalous NAO years Removing anomalous PNA years

39. Impact of Long-term trend? Median years: Small recurving dataset: 1982 Large recurving dataset: 1989 Can the median year difference be driving the entire flux difference? In such a case, the small recurving dataset should have STRONGER mean winter flux than the large recurving!! We see the opposite! 1980-2004 1955-1979

40. Summary Few recurving TCs: Few recurving TCs: Above normal early winter snowcover Above normal early winter snowcover Below normal subtropical upwelling Below normal subtropical upwelling Maximize land/ocean temp contrast Maximize land/ocean temp contrast Maximize pole/equator temp. contrast Maximize pole/equator temp. contrast Stationary eddies more intense Stationary eddies more intense Transients (cyclones) less intense, but more frequent Transients (cyclones) less intense, but more frequent Numerous recurving TCs: Numerous recurving TCs: Below normal early winter snowcover Below normal early winter snowcover Above normal subtropical upwelling Above normal subtropical upwelling Minimize land/ocean temp. contrast Minimize land/ocean temp. contrast Minimize pole/equator temp. contrast Minimize pole/equator temp. contrast Stationary eddies less intense Stationary eddies less intense Transients (cyclones) more intense, but less frequent Transients (cyclones) more intense, but less frequent

41. Unanswered questions Can we eliminate completely the possibility that there is a bigger forcing that is masterminding everything – such that TCs are just tracers and not active in this winter modulation? Can we eliminate completely the possibility that there is a bigger forcing that is masterminding everything – such that TCs are just tracers and not active in this winter modulation? Does the time, intensity, track, hemis. of recurv. TCs matter? Does the time, intensity, track, hemis. of recurv. TCs matter? Does the winter Rossby wave number of the planet have a preferred wave number depending on the prior recurving TC season due to? Does the winter Rossby wave number of the planet have a preferred wave number depending on the prior recurving TC season due to? What about a higher than normal frequency of TCs that remain in tropics? What about a higher than normal frequency of TCs that remain in tropics? Pump up APE or does Hadley Cell remove energy before winter begins? Pump up APE or does Hadley Cell remove energy before winter begins? How would the climate change (long-term) if TCs were not possible? How would the climate change (long-term) if TCs were not possible?

43. JFM Extratropical cyclone intensity distribution More frequent during winters following inactive recurving TC season More frequent during winters following active recurving TC season