TC’s role in climateTC’s role in climate

The bigger question: How would the The bigger question: How would the climate be different if TCs were not climate be different if TCs were not

“permitted” to form? “permitted” to form?

Energy transportEnergy transport

http://www.onr.navy.mil/focus/ocean/motion/currents1.htm

http://www.crh.noaa.gov/mqt/webpics/weatherpics/Big/thunderstorm%201.jpg

Relative Roles Relative Roles

Newton (1972)

Later revised by Trenberth et al.

Latent heatAtmosphere

Ocean

Total

Defining the TC role in Defining the TC role in climate:climate: TCs play a role in the energy transport, but the TCs play a role in the energy transport, but the

magnitude and nature varies considerably on a magnitude and nature varies considerably on a case by case basiscase by case basis

In the In the deepdeep tropics TCs greatly warm the tropics TCs greatly warm the atmosphere, but do not significantly cool the atmosphere, but do not significantly cool the ocean. Non-recurving TCs act to pump up the ocean. Non-recurving TCs act to pump up the tropical atmosphere:tropical atmosphere: Increase TIncrease TEQEQ-T-TPolePole

Recurving TCs cool the subtropical waters, and Recurving TCs cool the subtropical waters, and warm/moisten the midlatitude/polar warm/moisten the midlatitude/polar atmosphere: atmosphere: Decrease TDecrease TEQEQ-T-TPolePole

Do not necessarily remove the instability that Do not necessarily remove the instability that created themcreated them

One component of the TC One component of the TC rolerole

http://svs.gsfc.nasa.gov/vis/a000000/a001000/a001066/

How long does it take How long does it take for the upwelling-for the upwelling-induced cooling to induced cooling to return (warm) to return (warm) to climatology?climatology?

What is the What is the “atmospheric and/or “atmospheric and/or oceanic” memory of oceanic” memory of a TC’s passage?a TC’s passage?

Oceanic+Atmospheric Memory of Oceanic+Atmospheric Memory of TCsTCs

TC-induced oceanic coolingTC-induced oceanic cooling The time period for the MPI to The time period for the MPI to

return to climatology after a TC return to climatology after a TC passes: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 This MPI restoration to climatology is performed by:is performed by: Enhanced surface fluxesEnhanced surface fluxes Enhanced solar radiationEnhanced solar radiation Calendar catching upCalendar catching up

Aggregate impact is largest for Aggregate impact is largest for above normal frequency of above normal frequency of recurving TCsrecurving TCs

Hart, Watson, Maue (MWR 2007)Hart, Watson, Maue (MWR 2007)http://svs.gsfc.nasa.gov/vis/a000000/a001000/a001066/

By basinBy basin

Atmospheric memoryAtmospheric memory

Zoom in on Zoom in on atmosphere atmosphere

memorymemory

Another component of the TC roleAnother component of the TC roleTC-induced atmospheric warmingTC-induced atmospheric warming

HypothesisHypothesis In autumns when the recurving In autumns when the recurving

tropical cyclone activity is enhanced, tropical cyclone activity is enhanced, TCs have contributed more than TCs have contributed more than normal toward the heat redistributionnormal toward the heat redistribution

In these years, the subsequent role of In these years, the subsequent role of meridional temperature flux by other meridional temperature flux by other methods might be suppressed since methods might be suppressed since the midlatitudes/poles are warmer the midlatitudes/poles are warmer than normal (less work to be done)than normal (less work to be done)

Data & DefinitionsData & Definitions Northern hemisphere (NH) best-track tropical Northern hemisphere (NH) best-track tropical

cyclone record for 1955-2005:cyclone record for 1955-2005: North Atlantic + Eastern Pacific + Western Pacific North Atlantic + Eastern Pacific + Western Pacific

+ North Indian Basins+ 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 30A TC that forms equatorward of 30N and reaches N and reaches

a latitude of at least 40a latitude of at least 40N prior to dissipationN prior to dissipation

These TCs are argued to have contributed most These TCs are argued to have contributed most significantly to weakening the pole-to-equator significantly to weakening the pole-to-equator TT

Full disclosure…keep in mind Full disclosure…keep in mind we are ignoring:we are ignoring:

Whether the historical record truncated the trackWhether the historical record truncated the track The evolving quality of the historical recordThe evolving quality of the historical record When (month) the TC recurvesWhen (month) the TC recurves Where the TC recurvesWhere the TC recurves How intense the TC is when it recurvesHow intense the TC is when it recurves The role of Atlantic vs. Pacific recurversThe role of Atlantic vs. Pacific recurvers Larger scale impacts, such as volcanic eruptions, Larger scale impacts, such as volcanic eruptions,

that may mask the recurving TC impactthat may mask the recurving TC impact Long-term changes in climateLong-term changes in climate

Thus – this is not close to an optimized study of Thus – this is not close to an optimized study of the topicthe topic

Results: Recurving ClimoResults: Recurving Climo ““Inactive” yearsInactive” years

1956, 1968, 1970, 1971, 1977, 1979, 1982, 1956, 1968, 1970, 1971, 1977, 1979, 1982, 1983, 1984, 1986, 1987, 1988, 1991, 20021983, 1984, 1986, 1987, 1988, 1991, 2002

Mean year: 1980.3Mean year: 1980.3 Mean MEI: 0.50 (Neutral)Mean MEI: 0.50 (Neutral)

““Active” yearsActive” years 1955, 1959, 1962, 1972, 1975, 1976, 1989, 1955, 1959, 1962, 1972, 1975, 1976, 1989,

1993, 1994, 1995, 1996, 1997, 1998, 2001, 1993, 1994, 1995, 1996, 1997, 1998, 2001, 20052005

Mean year: 1984.5Mean year: 1984.5 Mean MEI: 0.12 (Neutral)Mean MEI: 0.12 (Neutral)

Results: Results: RecurvinRecurving Climog Climo

Western north PacificEastern north PacificNorth Atlantic

“Active” recurving TC years“Normal” recurving TC years

“Inactive” recurving TC years

Results: 51-year (1955-2005) Results: 51-year (1955-2005) recurving climatologyrecurving climatology

Mean number of NH recurving TCs is 9Mean number of NH recurving TCs is 9 Q1: 5 “inactive” recurving year thresholdQ1: 5 “inactive” recurving year threshold Q3: 12 “active” recurving year thresholdQ3: 12 “active” recurving year threshold

Surprisingly stable measure of Surprisingly stable measure of extremes:extremes: 1948-2005:1948-2005: Q1: 6, Q3: 12Q1: 6, Q3: 12 1955-2005:1955-2005: Q1: 5, Q3: 12Q1: 5, Q3: 12 1979-2005:1979-2005: Q1: 5, Q3: 12Q1: 5, Q3: 12

Range: 2-19 [hence, wildcard….]Range: 2-19 [hence, wildcard….]

Example Years: 1996 vs. 1977Example Years: 1996 vs. 1977

Images courtesy of Unisys

19 “Recurving” storms vs. 4 “recurving” storms

Results:Results:

500mb total meridional temperature 500mb total meridional temperature flux in winter following TC seasonflux in winter following TC season

JFM Winter following recurving TC season JFM Winter following recurving TC season Total 500mb temperature flux (NCEP/NCAR Total 500mb temperature flux (NCEP/NCAR

reanalysis)reanalysis)

ResultsResults 5-10% midlatitude 500mb JFM temp. 5-10% midlatitude 500mb JFM temp.

flux difference between:flux difference between: 5 recurving TCs and 12 recurving TCs5 recurving TCs and 12 recurving TCs

An average of 0.5-2% JFM midlatitude An average of 0.5-2% JFM midlatitude 500mb temp. flux reduction per TC, 500mb temp. flux reduction per TC, depending on reanalysis datasetdepending on reanalysis dataset

Next, examine stationary eddies onlyNext, examine stationary eddies only

Stationary Eddies Only Stationary Eddies Only [Long-term mean winter long-wave [Long-term mean winter long-wave

pattern]pattern]

Following inactive recurving season

Following active recurving season

Robustness / Significance: Stationary Robustness / Significance: Stationary Eddies onlyEddies only

Following inactive recurving season

Following active recurving season

Winter thickness following anomalous recurving Winter thickness following anomalous recurving TCsTCs

Winter temperature response to recurving TC Winter temperature response to recurving TC activityactivity

Winter precipitation response to recurving TC Winter precipitation response to recurving TC activityactivity

Jet Location / Strength & Jet Location / Strength & Hadley/Ferrell/Polar Cell ModulationHadley/Ferrell/Polar Cell ModulationPolar 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?

How does this anomalous How does this anomalous temperature patter vary in the temperature patter vary in the

vertical?vertical?

Jan. temp. Jan. temp. anomaly after TC anomaly after TC

seasonseason

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

The paradoxThe paradox The warm anomaly of a TC cools rapidly as The warm anomaly of a TC cools rapidly as

it reaches the higher lats. (emission as Tit reaches the higher lats. (emission as T44))

So, how does the impact of a recurving TC So, how does the impact of a recurving TC extend into the weeks to months to the extend into the weeks to months to the winter season?winter season? First: The First: The deepdeep tropics are largely a reservoir tropics are largely a reservoir

of heat, and thus warming of the higher of heat, and thus warming of the higher latitudes is not balanced by deep tropical latitudes is not balanced by deep tropical cooling [cooling [ net hemispheric warming] net hemispheric warming]

Second: Nonlinear impacts - snowcover Second: Nonlinear impacts - snowcover changeschanges

One method One method for for

nonlinear nonlinear extension of extension of TC impact?TC impact?

TC-induced TC-induced snowcover snowcover

anomalies that anomalies that lead to albedo lead to albedo changes up to changes up to

the start of the start of winter?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

What about a bigger What about a bigger forcing?forcing?

It is possible there is something It is possible there is something bigger, larger, that is forcing bigger, larger, that is forcing EVERYTHINGEVERYTHING

TC recurvature could be a tracer for TC recurvature could be a tracer for this bigger forcing mechanismthis bigger forcing mechanism

Maybe there is anomalous climate in Maybe there is anomalous climate in the spring/summer/fall that is the spring/summer/fall that is manipulating both the TC recurvature manipulating both the TC recurvature and the subsequent winter!and the subsequent winter! Prior autumn, Global warming, PNA, NAO, Prior autumn, Global warming, PNA, NAO,

AO, etcAO, etc

Is this Is this recurving recurving TC activity TC activity a response a response

to to baroclinic baroclinic activity of activity of

prior prior autumn?autumn?

No!!!!No!!!!

Impact of Global warming?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!

Impact of global warming?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!

Teleconnection Teleconnection masterminding? masterminding?

Removing anomalous AO years

Removing anomalous ENSO years

Removing anomalous NAO years

Removing anomalous PNA years

Impact of Long-term trend?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

SummarySummary Few recurving TCs:Few recurving TCs:

Above normal early winter snowcoverAbove normal early winter snowcover Below normal subtropical upwellingBelow normal subtropical upwelling Maximize land/ocean temp contrastMaximize land/ocean temp contrast Maximize pole/equator temp. contrastMaximize pole/equator temp. contrast Stationary eddies more intenseStationary eddies more intense Transients (cyclones) less intense, but more Transients (cyclones) less intense, but more

frequent frequent Numerous recurving TCs:Numerous recurving TCs:

Below normal early winter snowcoverBelow normal early winter snowcover Above normal subtropical upwellingAbove normal subtropical upwelling Minimize land/ocean temp. contrastMinimize land/ocean temp. contrast Minimize pole/equator temp. contrastMinimize pole/equator temp. contrast Stationary eddies less intenseStationary eddies less intense Transients (cyclones) more intense, but less Transients (cyclones) more intense, but less

frequentfrequent

Unanswered questionsUnanswered questions Can we eliminate completely the possibility that there Can we eliminate completely the possibility that there

is a bigger forcing that is masterminding everything – is a bigger forcing that is masterminding everything – such that TCs are just tracers and not active in this such that TCs are just tracers and not active in this winter modulation?winter modulation?

Does the time, intensity, track, hemis. of recurv. TCs Does the time, intensity, track, hemis. of recurv. TCs matter?matter?

Does the winter Rossby wave number of the planet Does the winter Rossby wave number of the planet have a preferred wave number depending on the prior have a preferred wave number depending on the prior recurving TC season due to?recurving TC season due to?

What about a higher than normal frequency of TCs What about a higher than normal frequency of TCs that remain in tropics? that remain in tropics? Pump up APE or does Hadley Cell remove energy before Pump up APE or does Hadley Cell remove energy before

winter begins?winter begins?

How would the climate change (long-term) if TCs were How would the climate change (long-term) if TCs were not possible?not possible?

JFM Extratropical cyclone intensity JFM Extratropical cyclone intensity distributiondistribution

More frequent during winters following inactive recurving TC seasonMore frequent

during winters following active recurving TC season