# Presentation: 125613

## Tropical Cyclone Precipitation Structures Derived from Reflectivity Statistics Using TRMM PR 

**Robert Rogers and Frank Marks **
**NOAA/AOML Hurricane Research Division**
**Krystal Valde**
**Univ. of Miami/CIMAS and NOAA/AOML Hurricane Research Division**
**Andrew Hagen**
**Department of Meteorology**
**Penn State University**

## Motivation

-  Radial, vertical, and temporal distributions of latent heating in tropical cyclones (TC’s) are key parameters in determining TC structure and intensity
-  While these parameters cannot be directly measured, radar reflectivity provides a proxy means of diagnosing details of the structure of convective and stratiform processes occurring within the TC
-  From these processes vertical motion and latent heating profiles can be inferred, yielding information on TC structure and intensity
-  TRMM Precipitation Radar provides valuable information that can be used for many purposes:
-  identify and compare structure of precipitation features in TC’s
-  compare statistics of precipitation structures across platforms and numerical models
-  compare precipitation structures as a function of storm parameters (e.g., storm intensity, location, environment)
-  identify possible differences in precipitation structures for different storm evolutions (e.g., rapid intensification, tropical cyclogenesis)

## Methodology

-  TRMM 2A25 Version 6 PR reflectivity profile dataset used
-  global dataset of tropical cyclone overpasses from 1998-2006
-  Partition areas into separate regions based on precipitation structure
-  eyewall, rainband, stratiform regions (for storms of hurricane strength only)
-  convective/stratiform partitioning (for systems of tropical depression, tropical storm, and hurricane strength)
-  partitioning based on vertical profile of PR reflectivity
-  Statistics of reflectivity profiles for different regions calculated and compared

## Precipitation structures diagnosed from TRMM PR

**Precipitation structures diagnosed from TRMM PR**

**Isabel 2003**

**A**

**B**

**A**

**B**

## Precipitation structures diagnosed from TRMM PR

**Mean reflectivity profiles for different storm regions**

**Precipitation structures diagnosed from TRMM PR**

**N=118 orbits**
**     ****64 storms**

## Precipitation structures diagnosed from TRMM PR

**eyewall**

**stratiform**

**rainband**

**Contoured Frequency by Altitude Diagrams (CFADs) for different regions**

**Precipitation structures diagnosed from TRMM PR**

**N=118 orbits**
**     ****64 storms**

## Comparison of precipitation structures from different platforms

**Height (km)**

**Height (km)**

**Height (km)**

**Height (km)**

**Reflectivity (dBZ)**

**Reflectivity (dBZ)**

**Reflectivity (dBZ)**

**Reflectivity (dBZ)**

**TRMM PR**

**Airborne radar**

**MM5**

**eyewall**

**stratiform**

**Comparison of precipitation structures from different platforms**

_**Reflectivity CFADs**_

**233 aircraft radial legs**
**9 TCs**

**96 output times ****∆x**** 1.67 km**
**2 TCs**

**118 TRMM PR swaths**
**64 TCs**

## Precipitation structure differences as a function of storm intensity

_**Mean reflectivity profiles**_

**Category 1**

**Category 3**

**Category 5**

**Precipitation structure differences as a function of storm intensity**

**N=118 orbits**
**     ****64 storms**

**N=82 orbits**
**    ****38 storms**

**N=20 orbits**
**    ****12 storms **

## Precipitation structure differences as a function of storm intensity

_**CFADs of reflectivity**_

**Category 1**

**Category 5**

**eyewall**

**stratiform**

**Precipitation structure differences as a function of storm intensity**

## Motivation

- There have been several studies linking convective bursts (CB) in TCs to rapid intensification (RI), but RI does not occur every time there is a CB
- To what extent is the occurrence (or non-occurrence) of RI after a CB governed by internal processes, e.g., structural characteristics of the CB, as opposed to external factors, e.g., vertical shear, sea-surface temperature, low- to mid-level humidity

**Precipitation structure differences in rapid intensification events**

## Which case underwent rapid intensification <18 hours later?

**Which case underwent rapid intensification <18 hours later?**

**1545 UTC Sept 19**

**0339 UTC Aug 30**

**1555 UTC Sept 19**

**0421 UTC Aug 30**

## Methodology

-  Used Atlantic storms only from 1998-2005
-  Identified CB cases, defined as:
- Half degree by half degree or larger area of <-70 oC cloud tops on GOES IR
- Must persist for at least 3 hours
- Center of CB must be within 200 km of center of storm
- CB must have at least some area of <190K brightness temperature using 85 GHz PCT
-  Associated CB cases with RI events, defined as 30-kt increase in maximum sustained winds in 24 hours by NHC’s Best Track.  RI had to occur within 24 h of CB.
-  Examined statistics of reflectivity fields from TRMM PR overpasses for RI (12 cases) and non-RI (15 cases) events that had a CB associated with them
-  Partitioned data into convective and stratiform regions, dependent on vertical profile of reflectivity

## Partitioning algorithm example

**Dolly 2002   43 kt          non-RI case**

**Partitioning algorithm example**

## Mean reflectivity profile in convective regions: RI vs. non RI

**Non RI**

**RI**

- Blue = non RI line;  Black = RI line

**Reflectivity (dBZ)**

**Height (km)**

## CFADs of Reflectivity in convective regions: RI vs. non RI

**CFADs of Reflectivity in convective regions: RI vs. non RI**

**RI**

**Non-RI**

## RI vs. non-RI profiles stratified by burst lifecycle stage

**RI vs. non-RI profiles stratified by burst lifecycle stage**

## RI vs. non-RI profiles stratified by storm intensity

**RI vs. non-RI profiles stratified by storm intensity**

**RI vs. non RI 50-75 kt**

## Summary 

- PR reflectivity profiles provide information on the vertical structure of different precipitation regions within tropical cyclones, can distinguish among them
- Distinct differences between platforms, biases from numerical models evident
- Reflectivity mean profiles extend higher (lower) for weaker (stronger) tropical cyclones, differences less pronounced for lower altitudes
- Reflectivity distributions are broader (narrower) for weaker (stronger) tropical cyclones
- Reflectivity profiles decrease less (more) rapidly with height at high altitude for systems that undergo (do not undergo) rapid intensification after a convective burst – vertical motions in the convective regions stronger in RI events?
- Differences in slope of reflectivity profiles evident for RI cases as a function of burst lifecycle stage, not so for non-RI cases
- Differences in slope of reflectivity between RI and non-RI cases evident for stronger tropical cyclones, not as evident for weaker tropical cyclones

## Future Work

- Continue to refine partitioning algorithms
- Compare simulated reflectivity statistics with TRMM PR, airborne radar using different model configurations (e.g., resolution, physical parameterizations)
- Expand comparisons of PR statistics to different parameters (e.g., different basins, environmental conditions)
- Increase sample size of RI vs. non-RI study (e.g., expand to other basins)
- Study environmental parameters as a factor in RI vs. non-RI (e.g., shear, SST, humidity)
- Can models reproduce observed variations in precipitation structure?
- Variations as a function of storm intensity
- Variations as they may relate to rapid intensification

## Supplementary slides

## About Sample

- 12 RI cases and 15 non-RI cases were used
- Used Atlantic storms only from 1998-2005
- I performed the analyses only for points within 300 km of the center of the storm

- Avg     62     47

## Some results from the non-radar part

- % <-60C cloud tops within 200 km of center:
- RI: 49.5%  stdev: 26.3%        non-RI: 33.9%  stdev: 15.4%
- Wind shear:
- RI: 10.2 kt  stdev: 3.6 kt	     non-RI: 18.8 kt  stdev:  9.0 kt
- STDEV in brightness temp:
- RI: 12.44                               non-RI: 22.89
- For all raining points in swath within 300 km of center of storm:
- RI cases: 11.3% of points are convective
- Non RI cases: 11.5% of points are convective

## Total points for PR data by region

**Total points for PR data by region**