1. Using Lightning Data to Monitor the Intensification of Tropical Cyclones in the Eastern North Pacific
By: Lesley Leary1, Liz Ritchie1,
Nick Demetriades2, Ron Holle2
1-University of Arizona
2-Vaisala Inc.
Acknowledgement: Sponsor Office of Naval Research Marine Meteorology Program
notes

2. Introduction: One cluster dissipates within 24 hrs.
One cluster develops into a category 2 hurricane
Which cluster will develop?
Cluster 1
Cluster 2

3. 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

4. Back to the clusters… 24 hours later Cluster 1 Cluster 1 Cluster 2

5. 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 UTC (10 pm Pacific)
Dissipated – August 24 at 1200 UTC (4 am Pacific)

6. 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

7. 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

8. 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
30 N
130 W
80 W
Equator

9. 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

10. 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 3
Cluster 1
Cluster 2
9/7/06 three clusters between 110 W and 130 W

11. Systems Over Water Developing Storms for 2006
Flash Counts (#/6h)
Non-Developing Clusters for July 2006
Flash Counts (#/6h)

12. Results: water systems
Developing Storms: tropical storms
Average flashes per 6 hrs:
Average flashes per storm: 5635
Total number flashes:
Presence of Diurnal Cycle
Non-Developing Clusters: tropical clusters
Average flashes per 6 hrs:
Average flashes per storm: 632
Total number flashes:
Presence of Diurnal Cycle

13. Systems Over Land Developing Storms for 2006
Flash Counts (#/6h)
Non-Developing Clusters for 2006 season
Flash Counts (#/6h)

14. Results for land systems
Developing Storms: tropical storms
Average flashes per 6 hrs: 1164
Average flashes per storm:
Total number flashes:
Presence of Diurnal Cycle
Non-Developing Clusters: 12 tropical clusters
Average flashes per 6 hrs: 336
Average flashes per storm: 5997
Total number flashes:
Presence of Diurnal Cycle

15. Is lightning really an accurate measure of intensification?
Non-Developing Clusters for August 2006
Notice cluster 6 – resembles results seen for developing systems
Is it really a developing system, or is lightning an inaccurate measure of tropical intensification?

16. QuikSCAT Cluster 6 Turning of winds 45 kt observation – underestimate
Why not designate as TD?

17. 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

18. 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