By: Tyler Sebree

Major: Atm. Sci.

Minor: Psychology

How Air-Sea Interactions Affect Hurricanes!

Sooo Much Physics & Math, but Please Bare with Me!

*Impacts of Air-Sea Interaction on Tropical

Cyclone Track and Intensity*

By: Liguang Wu, Bin Wang & Scott A. Braun

The Article!Hereeeee we go!

What Is A Hurricane???

Yet Again, Background Info.

Key Components: The Eye, Eye Wall, Central Dense Overcast, Outflow, Rainbands

Lifespan of a HurricaneTROPICAL STORM HURRICANE

Tropical Depression (winds < 38mph)Tropical Storm (39-73mph)Hurricane(> 74mph)

The Saffir-Simpson ScaleOtherwise known as the scale that measures a hurricane’s strength based on wind speed.

However, a category 1 can be just as CATASTROPHIC as a category 5 because of the many other components of a hurricane (coming up on the next slide).

1. Winds 2. Heavy Rainfall

Elements of a Hurricane

3. Storm Surge/Rip Tides4. Tornadoes

Purpose: determine relative roles of the weak

symmetric and strong asymmetric sea surface temperature anomalies relative to the tropical

cyclone center.

B/c other experiments didn’t…

Paper Time!

*SST anomalies that result from 3-D coupled models of hurricanes make up the axially symmetric and asymmetric components relative to the TC center1. Past studies say that the symmetric component of storm-induced

SST anomaly field could play a key role in lowering storm intensity2. Previous studies disagree regarding impacts of air-sea interaction

on TC motion. One experiment (south) attributed differences in TC track to asymmetric precipitation patterns that were shifted azimuthally (b/c I can’t think of any words to describe this word)…

3. Another experiment saw TC track to north. Suggested “that this track deviation is related to a systematic decrease in the azimuthally averaged tangential flow of the TC vortex”(Please do not ask about this statement -_- )

Vocab/Background

A. Determine if the symmetric SST anomalies are fully responsible for the lowering of storm intensity

B. To figure out why other studies have differing results regarding TC track

Paper’s Goals…

Well, the a/symmetric SSTanomalies are investigatednumerically with a coupledhurricane-ocean model.

Also, this study takes into account other studies’ contradictory results. Ex:the impacts of air-seainteraction on TC motion.

How It Went Down

…AND Experimental Design

Coupled Hurricane-Ocean Model

*First, we will look at the Hurricane Model component.Uses…1. 201 x 201 grid points w/ auniform spacing of 25 kmPrimary model physics…1. Large-scale condensation2. Subgrid-scale cumulus convection parameterized w/a Newtonian cooling 3. Surface fluxes of momentum,sensible and latent heat

Ocean Model*Oceanic response to forcing of moving TC can be divided into

TWO stages…1. Forced Stage Response: local response that includes OML

currents of 1m/s and considerable cooling of OML in right rear quadrant near vertical mixing (lasts ½ day)

2. Relaxation Stage Response: occurs after a TC passes; it is nonlocal & baroclinic in response to wind stress curl from TC

(lasts 5-10 days)

Coupled Model (Cont.)

~I’ll try to explain this sentence: “The energy is spread through internal waves that penetrate into the thermocline (see picture), and leaves behind a baroclinic geostrophic current along the storm track.”

To account for the above craziness, this ocean model must be accompanied by OML physics (YAY!) and thermocline and

upper ocean dynamics!

More Ocean Model!!

This experiment takes into account 2 oceanic components: OML & thermo.Finally, it’s math time!• Below thermocline layer is motionless deep layer (temp. T r

is constant)• In OML, temp. T1 and velocity are independent of depth• Thermocline layer = temp. decreases linearly from T1 to Tr

Equation relating variablesvertical temp. gradient in entrainment layer with thicknes is proportional to mean vertical temp. gradient in thermocline layer:

How about Some More Ocean Model?

Wish things were solved this way…

Experimental Design

Table showing the three sets of idealized numerical experiments and each of theirfour respective experiments

Different Experiments Conducted:

**Each set has 4 exp. conducted for it!

1. Fixed SST2. Coupled3. Symmetric-only SST

forcing4. Asymmetric-only SST

forcing

Table shows three sets of idealized numerical experiments with

differing environmental influences

Different Sets:

1. E1simplest case; run on an “f” plane with a horizontally uniform easterly ambient flow

2. E2on beta plane in resting environ.; vortex movement arises from beta drift

3. E3combination of E1 and E2

Experimental Design (Cont.)

Equation for the horizontal wind profile, v(r)…

Where r is the radius from the TC center & b is the shape

parameterAll experiments begin with an

identical, initially symmetric baroclinic vortex.

The max. tangential wind (Vm) of 25 m/s at rm = 100 km is at the lowest model level.

Where Do These Experiments Start?

Ocean Response in Coupled Model

-OML current increases quickly while the min. temp. decreases rapidly during first 24 hours

Ocean Response at 96 Hours

96 Hours (Cont.)

• Graph (a): sea surface temp. anomaly• Graph (b): mixed layer depth anomaly• Graph (c): entrainment rate• Graph (d): thermocline depth anomaly• Graph (e): Currents in the mixed layer• Graph (f): Currents in the thermocline layer

Both axes are distance in kilometerson all 6 graphs

--The TC intensities and tracks are compared with the corresponding fixed-SST experiments discussed previously…----------------------------------Figure: depicts the overall air-sea interaction phenomenon this is the large system that’s being discussed in this paper. ----------------------------------Its influence on TC intensity and track is crucial in terms of understanding TC’s strength and expected pathway

Results (Air-Sea Interaction on TCs)

Exp. E1

Results (I. Intensity Change)

Left side = time series of the max. wind speedRight side = min. central pressure

Exp. E2

Intensity Change (Cont.)

Exp. 3What these 6 graphs depict is the TC intensities for the three sets compared with the

corresponding fixed-SST exp. In terms of the max. wind speed and min. central pressure

*MAIN POINT: air-sea interaction reduces TC intensity because of mixed layer

coolingAsymmetric Component…

• Asymmetric SST field can affect TC intensity ONLY through the resulting

inner-core TC asymmetriesSymmetric Component…

• Overall, symmetric component plays key role in TC intensity

Intensity Change In Words

Results (II. TC Tracks)Part 1

TC tracks in fixed SST and coupled experiments (Left: E1 ; Right: E2)

TC TracksPart 2

E3 is on the left side and B2’s results are on the right side

TC TracksPart 3

B1 is on the left side & B3 is on the right sideQ: What do 6 graphs have in common?

A: Well, the TCs generally move westward in all scenarios

• Influence of air-sea coupling on TC tracks is small but persistent

• TCs in coupled exps. are displaced to the south compared to the corresponding exps.

without air-sea interaction• Asymmetric convection w/ respect to a TC

center can directly affect motion• Asymmetric-only forcing leads to increased

rainfall rate compared w/ the fixed SST exp. TWO REASONS WHY

• Intense hurricanes tend to be quite symmetric

Track Change in Words

Evolution of Rainfall Rates (Set E1)

Evolution of Rainfall (Set E2)

Evolution of Rainfall (Set E3)

• Background Info if we consider the cyclonic rotation of air parcels as they rise, the

enhanced rainfall rates are related to the positive SST anomalies ahead of the TC

center• Thus, these persistent rainfall

asymmetries typically shift the TC tracks marginally southward in coupled experiments of sets

E2 and E3

Why is Rain Important?

Conclusions1. Symmetric-only exp. results in northward moving storms

2. Asymmetric-only exp.results in southward moving storms

3. Fixed SST exps. are usedto show how the symmetric& asymmetric SST exps.affect TC movement

NOTES

• The three sets of numerical experiments—each of which has four exps. conducted for it—are used in this experiment overall• The results are compared to previous data, which enables

experimenters to produce major features of the ocean responses to moving TC forcing including OML deepening,

SST cooling, & OML & thermocline layer currents• Influence of asymmetric component is small symmetric

component cooling plays a key role in weakening TCs• Thus, evolution of TC can be simulated via only symmetric SST

decreases caused by air-sea coupling• Asymmetric SST forcing intensifies the rainfall rates on the

front left-hand side• Movement is variable depending on what component you are

looking at

OK, It’s The Last Conclusion Slide

• Well, I think the experiment is very accurate, precise & has credible background information

• The simplification of the information presented in the paper is not problematic in regards to the ending results

• I think the two components—intensity and track—of TCs are both undoubtedly affected by air-sea interaction, even if it is

only a slight amount• Also, I think there should be a continuance of

experimentation in this subfield of atmospheric sciences/climatology b/c there are other variables (i.e., sea spray) that weren’t taken into account in this experiment

• Lastly, I believe this b/c as time goes on and as the climate continues to evolve, TC components, configurations & characteristics could change, which could call for new experimentation being needed to study how air-sea

interactions manipulate TC track and intensity

Tyler’s Opinion