Cyclone Phase Space: One method to diagnose current

& forecast cyclone structureor

“Terapia para o ciclone com uma crise de identidade”

“Gustav” 2002 “Catarina” 2004

Motivation• Cyclones are not simply “tropical” or “extratropical”

• There is a great range of hybrid-type cyclones

• These are often the most challenging since we do not have conceptual models for them

• Do these cyclones exist because of competing energy sources?

• We will take a fresh look at the range of cyclone structure and propose a method to classify them all

Test: Separate the 5 tropical cyclones from the 5 non-tropical.

Images courtesy NCDC

Some relevant questions…• What makes a cyclone warm or cold-core?

• If all low pressure areas result from a column of air that is on average warmer than its environment, how can there be cold-core cyclones?

• What are the hydrostatic consequences of this thermodynamic structure & the resulting profile of cyclone “strength”?

• What about existence of mixed phase cyclones?

• Why do we care? 60 knots is 60 knots!

Some practical issues related to structure

The benefits and drawbacks of relying on climatology

Model interpretation: What type of development?

PMIN=1009hPa PMIN=1001hPa

PMIN=1003hPa PMIN=1005hPa

Why is the phase of a cyclone important?

• Predictability is a function of cyclone phase• Model interpretation/trust is a function of phase• It is often not at first apparent what the model is

forecasting, or the nature of cyclone development• Peak intensity is a function of cyclone phase

Additional relevance: Predictability

Additional relevance: Predictability

Non-conventional cyclones: Examples

1938 New England Hurricane

?

940hPa

Pierce 1939

• Began as intense tropical cyclone

• Rapid transformation into an intense hybrid cyclone over New England (left)

• Enormous damage ($5-10 billion adjusted to 2008). 10% of trees downed in New England. 600+ lives lost.

• Basic theories do not explain a frontal hurricane

12

21 December 1994

22 December 1994

23 December 1994 24 December 1994

Example of nonclassic structure

Non-conventional cyclones: ExamplesChristmas 1994

Hybrid New England Storm

NCDC

• Gulf of Mexico extratropical cyclone that acquired partial tropical characteristics

• A partial eye was observed when the cyclone was just east of Long Island

• Wind gusts of 50-100mph observed across southern New England

• Largest U.S. power outage (350,000) since Andrew in 1992

• Forecast 6hr earlier: chance of light rain, winds of 5-15mph.

Non-conventional cyclones: ExamplesCatarina (2004)

NCDC

• Demonstrates that we cannot rely purely on the historical record to diagnose and forecast structure

• What was Catarina?

• We can say it “looks” more like a hurricane than a significant number of north Atlantic hurricanes!

Summary of relevance:

• Classification

• Better understanding of the current state

• Applying conceptual models

• The type/extent of expected impact/damage

• Quantifying potential for intensity change and uncertainty– How can intensity change be forecast if there is great structural uncertainty?

• Amount of intrinsic (mis)trust of numerical model forecasts

The end result:We need a diagnosis of basic

cyclone structure that is more flexible than only tropical

or extratropical

Goal:A more flexible approach to cyclone characterization

To describe the basic structure of tropical, extratropical, and hybrid cyclones simultaneously using a cyclone phase space.

Phase Space

Parameter A

Par

amet

er B

Para

met

er C

What parameters to use?• Maximum wind? Minimum pressure?

– Too simple & does not discriminate

• Vorticity?– What level?

• Potential vorticity?– Separating vorticity and stability is important

• Q-vectors? – Does not simplify the continuum

• Energetics?– Ideal, but not practical in real-time

• Something more basic: thermal wind & asymmetry

Let us begin with a review the structure of the text-book cyclone types

Classic warm-core cyclone: TC

Low pressure results

from column of air on

average warmer than

environment, with the

anomalous warmth in

the troposphere

Source:

Advanced Microwave

Sounder (AMSU)

Temperature AnomalyImage courtesy Mark DeMaria, CIRA/CSU

www.cira.colostate.edu/ramm/tropic/amsustrm.asp

Hurricane Bonnie (1998) Temperature Anomaly12km

6km

1km

-

+

Classic warm-core cyclone: TC

TC Height Field (m) from hydrostatic balance

Warm: expansion of surfaces

Cold: contraction of height surface

Classic warm-core cyclone: TC

Height anomaly from zonal mean shaded

Height anomaly increases with

altitude in troposphere

Classic warm-core cyclone: TC

• Intensifies through: sustained convection, surface fluxes.

• Cyclone strength greatest near the top of the PBL

Gradient wind balance in a convective environ.

L

Wa rm

Cold

Z Troposphere

Stratosphere

Height anomaly

- +

Classic cold-core cyclone: Extratropical

L2.5 NCAR/NCEP reanalysis

Low pressure results from column of air

on average warmer than

environment, with the anomalous warmth in the stratosphere

Cleveland Superbomb Temperature Anomaly

Classic cold-core cyclone: Extratropical

Height anomaly from zonal mean shaded

Height anomaly decreases with

altitude in troposphere

Classic cold-core cyclone: Extratropical• Intensifies through: baroclinic development, tropopause

lowering.

• Cyclone strength greatest near tropopause

QG balance in a minimally convective environ

L

Cold

Warm

Z Troposphere

Stratosphere

Height anomaly over sfc center

- +

Warm

Cold

Hybrid (non-conventional) cyclone

Troposphere

Stratosphere

Colder

Warmer

Z

Warmer

L Height anomaly over sfc center

- +

What if an occluded extratropical cyclone moves over warm water? Characteristics of tropical and extratropical cyclones.

Cyclone Parameters 1 and 2: Vertical structure -VT: Thermal Wind [Warm vs. Cold Core]

Height anomaly

- +

Height anomaly

- +

Height anomaly

- +

Warm core Hybrid Cold Core

300mb

600mb

900mb

Cyclone Parameter -VT: Thermal Wind

Warm-core example: Hurricane Floyd 14 Sep 1999

Z

Z

Z

Z

Z

Z

Z

Z

Z

||ln

)(600

900

LT

hPa

hPa

MINMAX Vp

ZZ

||ln

)(300

600

UT

hPa

hPa

MINMAX Vp

ZZ

Two layers of interest

Vertical profile of ZMAX-ZMIN is proportional

to thermal wind (VT).

||ln

)(T

MINMAX Vp

ZZ

Cyclone Parameter -VT: Thermal Wind

Cold-core example: Cleveland Superbomb 26 Jan 1978

||ln

)(600

900

LT

hPa

hPa

MINMAX Vp

ZZ

||ln

)(300

600

UT

hPa

hPa

MINMAX Vp

ZZ

Third dimension?• We now have two parameters of the CPS that

discriminate the vertical structure of a cyclone: warm vs. cold vs. hybrid core

• What about the horizontal structure?

• How do we separate the horizontal structure of the various types of cyclones?

• Ultimately, a good measure is frontal nature (baroclinic vs. barotropic structure)

Cyclone Parameter 3: Horizontal structureB: Thermal Asymmetry

Symmetric Hybrid Asymmetric

• Defined using storm-relative 900-600hPa mean thickness field (shaded) asymmetry within 500km radius:

B >> 0: Frontal B0:Nonfrontal

Cyclone Parameter B: Thermal Asymmetry

3160

m32

60mL

Cold Warm

LhPahPa

RhPahPa ZZZZB 900600900600

Cyclone Parameter B: Thermal Asymmetry

L L L

Developing Mature Occlusion

B >> 0 B > 0 B 0

Conventional Extratropical cyclone: B varies

L L L

Forming Mature Decay

Conventional Tropical cyclone: B 0

Constructing Phase Space

Constructing 3-D phase space from cyclone parameters: B, -VT

L, -VTU

A trajectory within 3-D generally too complex to visualize in an operational setting

Take two cross sections (slices) :

B

-VTL

-VTU

-VTL

Hurricane Mitch (1998)

Case of symmetric, warm-core development and decay

Classic tropical cyclone

Symmetric warm-core evolution: Hurricane Mitch (1998)Slice 1: B Vs. -VT

L

Symmetric warm-core evolution: Hurricane Mitch (1998)Slice 1: B Vs. -VT

L

Symmetric warm-core evolution: Hurricane Mitch (1998)Slice 2: -VT

L Vs. -VTU

Upward warm core development maturity, and decay.

With landfall, warm-core weakens more rapidly in lower troposphere than upper.

Symmetric warm-core evolution: Hurricane Mitch (1998)Slice 2: -VT

L Vs. -VTU

Upward warm core development maturity, and decay.

With landfall, warm-core weakens more rapidly in lower troposphere than upper.

December 1987 Extratropical Cyclone

Case of asymmetric, cold-core development and decay

Classic occlusion of an extratropical cyclone

Asymmetric cold-core evolution: Extratropical CycloneSlice 1: B Vs. -VT

L

Asymmetric cold-core evolution: Extratropical Cyclone Slice 2: -VT

L Vs. –VTU

Hurricane Floyd (1999)

Multiple phase evolution:

Case of extratropical transition of a tropical cyclone

Warm-to-cold core transition: Extratropical Transition of Hurricane Floyd (1999): B Vs. -VT

L

-VTL

B

1 2

3

45

1

2

3

45

Warm-to-cold core transition: Extratropical Transition of Hurricane Floyd (1999)

B Vs. -VTL

Provides for objective indicators of extratropical transition lifecycle.

Extratropical transition begins when B=10m

Extratropical transition ends when –VT

L < 0

-VTL

B

Spaghetti Plot of 34 Cyclone Phase Trajectories based upon Navy NOGAPS operational analyses

B

-VTL

960hPa 970hPa 980hPa 990hPa 1000hPa 1010hPa

Symmetric Warm Core

Asymmetric Warm-core

Symmetric Cold-core

Asymmetric Cold-Core

TE

TE+24h

TE+48h

TB

TMID

TB-24h

TB-48h

34-Cyclone Composite Mean Phase NOGAPS-analysis based Trajectory with key milestones labeled

Composite Mean ET Structural Evolution Summary

TB-72h

TE+72h

Boxes represent the calculated one standard deviation spread about the 34-cyclone consensus mean trajectory for each time

Variability About the Composite Mean

Considerable variability about mean once transition completed=> posttropical phase can take many forms….

Floyd (1999): Non-intensifying cold-core development

Hugo (1989): Explosive cold-core development

Charley (1986): Schizophrenia

Dennis (1999): “ET-Interruptus”.Cindy (1999): Absorption.

Keith (1988): Explosive warm-seclusion development

Hurricane Olga (2001)

Multiple phase evolution:

Case of tropical transition of a cold-core cyclone

Cold-to-warm core transition: Tropical Transition of Hurricane Olga (2001)

-VTU Vs. -VT

L

Cold-to-warm core transition: Tropical Transition of Hurricane Olga (2001)

-VTU Vs. -VT

L

-VTL

-VTU

Tropical transition begins when –VT

L > 0

(subtropical status)

Tropical transition completes when –VT

U > 0

(tropical status)

Catarina: What was it in this context?

Summary of cyclone types within the phase space

Summary of cyclone types within the phase space

?Polar lows?

Phase space limitations

• Cyclone phase diagrams are dependent on the quality of the analyses upon which they are based.

• Three dimensions (B, -VTL, -VT

U) are not expected to explain all aspects of cyclone development

• Other potential dimensions: static stability, long-wave pattern, jet streak configuration, binary cyclone interaction, tropopause height/folds, surface moisture availability, surface roughness...

• However, the chosen three parameters represent a large percentage of the variance & explain the crucial structural changes.

Important Caveats:

Often model analysis representation is poor

Important Caveats: Warm Seclusion Dilemma

• At middle to higher latitudes, often winter-type cyclones will develop tropical-type structure– Warm core

– Eye

– Extreme intensity

• These cyclones often are “the worst of both worlds”– Tropical

– Extratropical

• They represent the largest forecast problems for oceanic forecasting

Forecast South Atlantic Warm Seclusion this week

Cold-Core Post-transition ET

Warm Seclusion Post-transition ET

Surface wind field of a warm seclusion

Figure courtesy Ryan Maue, FSU

40kt, 75kt, 90kt

Vertical structure of a warm seclusion

Figure courtesy Ryan Maue, FSU

Warm core to the west, cold core to the east!!

Revisit: Why is the phase of a cyclone important?

• Predictability is a function of cyclone phase• Model interpretation/trust is a function of phase• It is often not at first apparent what the model is

forecasting, or the nature of cyclone development• Peak intensity is a function of cyclone phase

Cyclone Phase Forecasting & Real-time Web Site

Real-time Cyclone Phase Analysis & Forecasting

• Phase diagrams produced in real-time for various operational and research models.

• Provides insight into cyclone evolution that may not be apparent from conventional analyses

• Web site: http://moe.met.fsu.edu/cyclonephase

• Also available a historical archive of CPS diagrams for nearly 100 cyclones

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Cyclone Phase Web Page Overview• Model analyses and forecast-based phase

diagrams:– GFS (0,6,12,18 UTC)– CMC (0,12 UTC)– GFDL (0,6,12,18 UTC)– HWRF (0,6,12,18 UTC)– MM5 (FSU) (0,12 UTC)– NAM (0,6,12,18 UTC)– NOGAPS (0,12 UTC)– UKMET (0,6,12,18 UTC)

71

• Trajectory through phase space describes structural evolution– A = When cyclone was first detected– C = Current analysis time– Z = Cyclone dissipation time or end of model forecast data– AC = cyclone structural history– CZ = cyclone structural forecast– Date is labeled at 00Z along phase trajectory

• Color of trajectory gives cyclone intensity in MSLP

• Size of marker gives average radius of 925hPa gale-force wind

• Cyclone track & underlying SST provided in inset

• Phase diagram quadrants are shaded to give more rapid interpretation

Cyclone Phase Web Page Overview

Example real-time cyclone availability for GFS

Example GFS forecast oceanic extratropical cyclone

Forecast phase analysis

Zoomed

Ensembling

Structural Predictability

Sensitivity to initial conditions & physics• Often there is phase dependency on the type of

data assimilation or model physics

11 November 2003 GFDL vs GFS AVN

Multiple model solutions: Measure of structural forecast uncertainty

Multiple model solutions: Measure of structural forecast uncertainty

78

Tropical Storm Noel: GFS ENS

79

Tropical Storm Noel: GFS ENS

80

CPS provides a method to verify model cyclone

structure forecasts

GFS ANALYSIS GFS 5-day FORECAST

DIFFERENCE

Closing thoughts• They have been shown to be very helpful for:

– Understanding the current analysis of a cyclone– Understanding the subtlety among many models– Quantifying the timing of

• Extratropical to tropical transition• Tropical to extratropical transition• Genesis

– Used by NHC, CHC, JTWC, JMA [approx 100 citations]

• We must remember they cannot replace other tools– If used, they should be in addition to other tools– They are only as useful as the source data

• We always welcome new model output to the web page

Obrigado

Extra Slides

Three key subcomposites

• Fast [<=12hr] vs. Slow [>=48hr] Transitioning

• Post-ET Intensification (N=6) vs. Weakening (N=11)

• Post-ET Cold-Core (N=15) vs. Warm-Seclusion (N=6)

TB: Fast (left) vs. Slow (right) Transitioning

500mb Height

& Anom.

SST & Anom.

TB: Post-ET Weakening (left) vs. Intensification (right)

Strengthen (N=6)

500mb Height

& Anom.

SST & Anom.

TE: Post-ET Cold-core (left) vs. warm-seclusion (right)

Strengthen (N=6)

320K PV

320K PV