Using Lightning Data to Monitor the Intensification of Tropical Cyclones inthe Eastern North Pacific

By: Lesley Leary1, Liz Ritchie1, Nick Demetriades2, Ron Holle2

1-University of Arizona2-Vaisala Inc. Acknowledgement: Sponsor Office of Naval Research Marine Meteorology Program

Introduction:•One cluster

dissipates within 24 hrs.

•One cluster develops into a category 2 hurricane

•Which cluster will develop?

Cluster 1

Cluster 2

Understanding Genesis•Definition:▫Processes that occur in a tropical disturbance

prior to tropical depression designation.•Forecasting:▫When and where tropical systems will develop▫Which clusters will develop

• Important factors:▫Synoptic-scale pattern▫SSTs▫Vorticity▫Vertical profile of atmosphere

Back to the clusters…24 hours later

Cluster 1

Cluster 2

Cluster 1

Cluster 2

24 more hours…Hurricane Hector • Began as a convective cluster on

August 13 at 0000 UTC (4 pm Pacific)

• Skipped TD status• TS status - August 16 at 0000 UTC

(4 pm Pacific)• Maximum intensity - August 18 at

0600 UTC (10 pm Pacific)• Dissipated – August 24 at 1200 UTC

(4 am Pacific)

Why Lightning is Interesting

• Lightning requires deep convection• Intensity of convection may indicate

development of the cloud cluster into a TC• Frequency of lightning can imply intensity of

convection• Periods of increased activity in lightning can

indicate diurnal cycle in organized systems• Means of tracking convective tropical systems

Hypothesis• If lightning can be

used as a measure of convective activity, it may be able to be an indicator of whether tropical cyclogenesis and/or intensification will occur in a given disturbance. Hurricane Floyd:

September 14, 1999

Long-Range Lightning Detection Network

•Extension of National Lightning Detection Network

•Detects VLF signals trapped by ionosphere

•Efficiency of network decreases with▫Distance from coast▫Time of day

•Using data from 2006

130 W 80 W

30 N

Equator

Methodology: Developing Systems•Genesis:•No time requirement for genesis period• Track system with IR imagery every 6 hrs.

for entire lifetime of the system•Allows the capture of any possible pattern

during genesis period•Classify as land or water storm•Create a longitude/latitude boundary for

each period•Filter lightning data per 6 hr. period for

each system

Methodology: Non-Developing Clusters

• Track persistent clusters within the region▫ Exclude clusters lasting less

than 72 hrs unless: Out of range Joins another cluster

• Classify storm as land or water cluster

• Create boundaries and filter lightning data with same method as developing systems

Cluster 1

Cluster 2

Cluster 3

9/7/06 three clusters between 110 W and 130 W

Developing Storms for 2006

Non-Developing Clusters for July 2006

Systems Over Water

Flas

h C

ount

s (#

/6h)

Flas

h C

ount

s (#

/6h)

Results: water systems• Developing Storms:

9 tropical storms▫ Average flashes per 6 hrs:

270▫ Average flashes per

storm: 5635▫ Total number flashes:

50713• Presence of Diurnal Cycle

• Non-Developing Clusters: 47 tropical clusters▫ Average flashes per 6 hrs:

37▫ Average flashes per

storm: 632▫ Total number flashes:

29734• Presence of Diurnal Cycle

local time total flashes % of total4 pm- 10 pm 15183 29.94%10 pm- 4 am 21945 43.27%4 am- 10 am 9207 18.16%10 am- 4 pm 4378 8.63%

local time total flashes % of total4 pm- 10 pm 9226 31.03%10 pm- 4 am 12685 42.66%4 am- 10 am 4078 13.71%10 am- 4 pm 3687 12.40%

Systems Over Land

Developing Storms for 2006

Non-Developing Clusters for 2006 seasonFl

ash

Cou

nts

(#/6

h)

Flas

h C

ount

s (#

/6h)

Results for land systems• Developing Storms:

5 tropical storms▫ Average flashes per 6 hrs:

1164▫ Average flashes per

storm: 19362▫ Total number flashes:

96632• Presence of Diurnal Cycle

• Non-Developing Clusters: 12 tropical clusters▫ Average flashes per 6 hrs:

336▫ Average flashes per

storm: 5997▫ Total number flashes:

71962• Presence of Diurnal Cyclelocal time total flashes % of total7 pm- 1 am 17479 24.29%1 am- 7 am 34244 47.59%7 am- 1 pm 9825 13.65%1 pm- 7 pm 10412 14.46%

local time total flashes % of total7 pm- 1 am 20632 21.35%1 am- 7 am 53582 55.45%7 am- 1 pm 12537 12.97%1 pm- 7 pm 9881 10.23%

Is lightning really an accurate measure of intensification?

Notice cluster 6 – resembles results seen for developing systems

Is it really a developing system, or is lightning an inaccurate measure of tropical intensification?

Non-Developing Clusters for August 2006

QuikSCAT• Turning of winds• 45 kt observation –

underestimate• Why not designate

as TD?

Cluster 6

Conclusions• The results we have presented indicate that

lightning activity is a good indicator of whether a cloud cluster will develop into a tropical depression

• Lightning is a proxy for deep convection, so this leads us to the question of how convective processes are important in the genesis process

• Storms over land have more convective activity than storms over water – it appears to be easier to differentiate between developing and non-developing systems over water

Future Work• Expand the data set to include multiple seasons and

look for statistically significant trends in the data• Investigate the reasons for the unusual diurnal signal

in the land-based systems• Analyzing lightning data for storms after TS

designation to look for signatures in intensification• Examine other remotely sensed data that may

differentiate between tropical clusters and developing storms

• Identify a signature that can predetermine whether genesis will occur in a cluster