# Presentation: 369411

## Effects of Environmental Moisture on Tropical Cyclone Precipitation: Land/Ocean DifferenceHaiyan Jiang1, Jeffrey B. Halverson2, and Edward J. Zipser1 1Department of Meteorology, University of Utah, Salt Lake City, Utah2Joint Center for Earth Systems Technology, University of Maryland, Baltimore County, Baltimore, MarylandContact: h.jiang@utah.edu 

**Effects of Environmental Moisture on Tropical Cyclone Precipitation: Land/Ocean Difference*****Haiyan Jiang******1******, Jeffrey B. Halverson******2******, and Edward J. Zipser******1****** ******1******Department of Meteorology, University of Utah, Salt Lake City, Utah******2******Joint Center for Earth Systems Technology, University of Maryland, Baltimore County, Baltimore, Maryland******Contact: h.jiang@utah.edu ***
***Poster this afternoon “Contribution of Tropical Cyclones to Global Precipitation from 9 Years of TRMM  Data.....”***

## Background

- One of the current Tropical Cyclone (TC) rainfall forecast techniques --  R-CLIPER (Lonfat et al. 2004, 2007): uses mainly **TC intensity to predict TC rainfall** with some additional parameters such as TC motion, topography, and vertical wind shear
- Previous TC case studies by L. Bosart et al. used environmental moisture parameters to diagnose TC rainfall
- Water Vapor Budget Equation:
**    ****P** = *Local Change of  TPW* + **HMC** + **OSF **– *Cloud Storage*** **
**    ****P: Precipitation**
**    ****TPW: Total Precipitable Water**
**    ****HMC: Horizontal Moisture Convergence**
**    ****OSF: Ocean Surface Flux**
**    ***Local change of TPW and Cloud Storage terms are insignificant.*
*    **But TPW itself is important because it is related to HMC.*

## Objectives

- Statistically quantify dependence of TC rainfall on Total Precipitable Water (TPW), Horizontal Moisture Convergence (HMC), and Ocean Surface Flux  (OSF) using a 7-yr (1998-2004) TRMM 3B42 database for 36 North Atlantic landfalling storms.
- How do these effects differ between land/ocean conditions?
- Isolate dependence on TPW, HMC, and OSF from dependence on storm strength

## Data

- 7 years (1998-2004) of TRMM 3B42 data (3 hourly, 0.25x0.25 degree lon/lat resolution) for 36 North Atlantic landfalling Tropical Cyclone (TC) database: total 2631 overpasses, of which 452 (1960) are over-land (over-ocean). Over-land (over-ocean) overpass is defined such as 60% of the raining area are over land (over ocean). For each storm, the average life time is about 9 days with about 6-7 days over ocean and about 1-2 days over land.
- NOGAPS analysis (12 hourly, 1x1 degree lon/lat resolution) is used for obtaining environmental moisture parameters: Total Precipitatible Water (TPW), Horizontal Moisture Convergence (HMC), and Ocean Surface Flux (OSF).

## Parameters We Analyze

**In storm-relative coordinates, we compute: **
** ****1. Rain Parameters: **
**    ****1) Radial Distribution of Azimuthally Averaged Rain Rates up to 5 degree radius (~555 km)**
**    ****2) Volumetric Rain within 5 degree radius**
** **

**2. Moisture Parameters: **
** ****1) Mean Total Precipitatible Water (TPW) within 5 degree radius**
** ****2) Mean Horizontal Moisture Convergence (HMC) within 5 degree radius**
** ****3) Mean Ocean Surface Flux (OSF) within 5 degree radius**

## Result 1: 

**Radial Distributions of Azimuthally Mean Rain Rate as a Function of Maximum Wind Speed, Mean Total Precipitable Water (TPW), Mean Horizontal Moisture Convergence (HMC), and Mean Ocean Surface Flux (OSF) **

## Azimuthally Mean Rain Rate as a Function of Maximum Wind Speed 

**Azimuthally Mean Rain Rate as a Function of Maximum Wind Speed **

## Azimuthally Mean Rain Rate as a Function of Mean Total Precipitable Water (TPW) Within 5 Degree Radius 

**Azimuthally Mean Rain Rate as a Function of Mean Total Precipitable Water (TPW) Within 5 Degree Radius **

## Azimuthally Mean Rain Rate as a Function of Mean Horizontal Moisture Convergence (HMC) Within 5 Degree Radius 

**Azimuthally Mean Rain Rate as a Function of Mean Horizontal Moisture Convergence (HMC) Within 5 Degree Radius **

## Azimuthally Mean Rain Rate as a Function of Mean Ocean Surface Flux (OSF) Within 5 Degree Radius 

**Azimuthally Mean Rain Rate as a Function of Mean Ocean Surface Flux (OSF) Within 5 Degree Radius **

## Result 2: 

**2D Histograms of TC Volumetric Rain within 5 Degree Radius vs. Maximum Wind Speed, Mean Total Precipitable Water (TPW), Mean Horizontal Moisture Convergence (HMC), and Mean Ocean Surface Flux (OSF) **

## 2D Histogram (Relative Frequency) of TC Volumetric Rain within 5 Degree Radius and Maximum Wind Speed 

**2D Histogram (Relative Frequency) of TC Volumetric Rain within 5 Degree Radius and Maximum Wind Speed **

**                                               ****ALL Samples        Land               Ocean**
**Correlation Coefficient:       r=0.52                   r=0.44              r=0.50**

## 2D Histogram (Relative Frequency) of TC Volumetric Rain within 5 Degree Radius and Mean Total Precipitable Water (TPW) within 5 Degree Radius

**2D Histogram (Relative Frequency) of TC Volumetric Rain within 5 Degree Radius and Mean Total Precipitable Water (TPW) within 5 Degree Radius**

**                                               ****ALL Samples        Land               Ocean**
**Correlation Coefficient:         r=0.52                 r=0.36              r=0.51**

## 2D Histogram (Relative Frequency) of TC Volumetric Rain within 5 Degree Radius and Mean Horizontal Moisture Convergence (HMC) within 5 Degree Radius

**2D Histogram (Relative Frequency) of TC Volumetric Rain within 5 Degree Radius and Mean Horizontal Moisture Convergence (HMC) within 5 Degree Radius**

-                                                **ALL Samples        Land               Ocean**
**Correlation Coefficient:       r=0.61                   r=0.58              r=0.60**

## 2D Histogram (Relative Frequency) of TC Volumetric Rain within 5 Degree Radius and Mean Ocean Surface Flux (OSF) within 5 Degree Radius

**2D Histogram (Relative Frequency) of TC Volumetric Rain within 5 Degree Radius and Mean Ocean Surface Flux (OSF) within 5 Degree Radius**

-                                                **ALL Samples        Land               Ocean**
**Correlation Coefficient:       r=0.49                   r=0.42              r=0.46**

## 2D Histogram (Relative Frequency) of TC Volumetric Rain within 5 Degree Radius and Mean (HMC+OSF)within 5 Degree Radius

**2D Histogram (Relative Frequency) of TC Volumetric Rain within 5 Degree Radius and Mean (HMC+OSF)****within 5 Degree Radius**

-                                                **ALL Samples        Land               Ocean**
**Correlation Coefficient:       r=0.66                   r=0.64              r=0.64**

## Summary of Previous Linear Correlation Coefficients

**Summary of Previous Linear Correlation Coefficients**

**Multiple Linear Correlation Coefficients**

## Detailed Analysis on Top 10% of Volumetric Rain From Total 452 Over Land Samples

**Detailed Analysis on Top 10% of Volumetric Rain From Total 452 Over Land Samples**

## Summary

**1. TC rainfall is correlated with environmental moisture parameters, such as Total Precipitable Water (TPW), Horizontal Moisture Convergence (HMC), and Ocean Surface Flux (OSF). **
**2. The correlation coefficients between volumetric rain and moisture parameters are generally higher for over ocean conditions than those for over land conditions. This is also the case for correlation coefficients between volumetric rain and maximum wind speed.**
**3. By adding moisture parameters as additional variables, TC volumetric rain will be better predicted than using TC intensity (max. wind speed) only. The correlation coefficient between volumetric rain and max wind speed can increase from 0.50 (0.44) to 0.69 (0.66) for over ocean (land) conditions by adding TPW, HMC and OSF.**

## Thanks for you attention!

## Back-up Slides

## Dependence of Moisture Parameters on Maximum Wind Speed

**Dependence of Moisture Parameters ****on Maximum Wind Speed**

## Azimuthally Mean Rain Rate as a Function of Ocean Surface Flux (OSF) Within 5 Degree Radius 

- After 3 data entries are removed.
- These 3 observations are Floyd (1999 091609, 091612; maxwind=80&70kt) and Isidore (2002092612, maxwind=55kt).

- After 55 data entries are removed.
- These 55 observations are from Floyd (1999,maxwind=97.5~135kt) and Isabel (2003;maxwind=90~137 kt).

## Slide 24