# Presentation: 693212

## Aircraft Observations of the Hurricane Boundary Layer Structure

- Jun Zhang
- Collaborators: William Drennan, Peter Black, Jeffrey French, Frank Marks, Kristina Katsaros, and Susanne Lehner
-              National Hurricane Center, Feb. 6th, 2009

##     Hurricane intensity is related to:

Environmental control;
Ocean feedback;
Cloud Microphysics;
......

Physical processes near the air-sea interface across the boundary layer

    The Hurricane boundary  layer is the least well observed part in a storm till now

- Environmental control;
- Ocean feedback;
- Cloud Microphysics;
- ......
- Physical processes near the air-sea interface across the boundary layer
-     The Hurricane boundary  layer is the least well observed part in a storm till now

**Notes:**
Add a track forecast with intensity forecast ability

## Outline

- Background and Motiviations;
- Experiment and Instrumentation;
- Results: 1) turbulent fluxes and parameterization
-                     2) vertical structure of turbulence
-                     3) Turbulent Kinetic Energy (TKE) budget
-                     4) Boundary layer rolls
-                     5) Hurricane boundary layer height
- 4.   Summary and Future Work.

## Depiction of the ABL processes

- http://www.esrl.noaa.gov/research/themes/pbl/

- ------- Boundary layer height

**Notes:**
Simple Basic boundary layer schematic showing a boundary layer hurricane is a unique flow that has rotation components.

## Why is the boundary layer so important in hurricanes?

**Why is the boundary layer so important in hurricanes?**

**The boundary layer provides a powerful coupling between the**** ****primary circulation**** ****(the azimuthal component) and the**** ****secondary circulation**** ****(the radial-vertical, or “in-up-and-out” component).**
**Moisture enters a hurricane from the sea surface and its radial distribution is strongly influenced by that of the boundary layer winds.**
**The boundary layer dynamics and thermodynamics determine the vertical transport of moisture and angular momentum out of the boundary layer.**
**The radial distribution of these quantities on leaving the layer exerts a strong constraint on the radial distribution of buoyancy.**

- Courtesy of Roger Smith

## Emanuel (1995):

- Axisymmetric model
- Slab boundary layer
- Use gradient wind
- Bulk BL parameterization
-     CD drag coefficient (momentum)
-     CK enthalpy coefficient

- CK/CD ~ 1.2 – 1.5
-     CK/CD > 0.75

## Surface Fluxes and Parameterizations

## MM5 simulation of Hurricane Bob (1991)

**MM5 simulation of Hurricane Bob (1991)**

**Braun and Tao, 2000**

**Sensitivity to boundary-layer parameterization**

****** ****Skillful prediction of intensity change requires an accurate representation of the boundary layer and parameterization of surface fluxes.**

## Powell et al. 2003

- O  AGILE    (Donelan & Drennan 1995)
- X  HEXOS  (DeCosmo et al 1996)
- ◊   GASEX  (McGillis et al 2004)
-     SOWEX (Banner et al 1999)
- □  SWADE  (Katsaros et al 1993)

- COARE-3     ---
- COARE 2.5  —

- EC Data from 8 field experiments : AGILE, AWE, ETCH,GASEX,HEXOS,RASEX, SHOWEX, SWADE, WAVES (4322 pts).
- —   Smith (1980)

- Donelan et al. 2004

## Prior to 2003, the only boundary layer in-situ turbulence structure measurement was conducted by Moss (1978) in the periphery of marginal hurricane Eloise (1975) at surface wind speed of about 20 m/s. 

- Prior to 2003, the only boundary layer in-situ turbulence structure measurement was conducted by Moss (1978) in the periphery of marginal hurricane Eloise (1975) at surface wind speed of about 20 m/s.

- Moss (1978)

- Zi

## 2002: 3 Test flights in Hurricanes Edouard, Isidore, and Lili2003: 6 flights in Hurricanes Fabian and Isabel2004: Flights at top of boundary layer, only 2 flux flights in  Hurricanes Frances and JeanneBlack et al. 2007 BAMSDrennan et al. 2007 JASFrench et al. 2007 JASZhang et al. 2008 GRL

- The Coupled Boundary Layer Air-sea Transfer Experiment (CBLAST)

**N43RF flux instrumentation**
**-  BAT (“Best Aircraft Turbulence”) probe on boom **
**-  Rosemount Gust probes in radome and fuselage**
**-  Inertial navigation, GPS systems in fuselage**
**- ****LICOR LI-7500 hygrometer (modified)**
**- Rosemount temperature sensors**
**- PRT5 radiometer for sea surface temperature  **
**- Stepped Frequency Microwave Radiometer (SFMR) **

**←****LICOR **
**     ****head**

-  ↓ BAT

_**CBLAST STEPPED DESCENTS**_

- 108 flux runs for momentum flux measurement
- 42 flux runs for enthalpy flux measurement

- Black lines represent the flux runs
- Typical length of a flux run is 24 km

## Vertical profiles of Mean Flow(Data are from measurements during Sept. 12th 2003)

- Vertical profiles of Mean Flow(Data are from measurements during Sept. 12th 2003)

- zi

- To Eye

## Time series for a typical flux run 

- Time series for a typical flux run

- (40 Hz data)

## Spectral Analysis

**Notes:**
Maybe delete this slide

## Drag Coefficients

- Smith (1992) ------
- Large and Pond (1980) ------
- Smith (1980) -------
- COARE 3.0 —
- CBLAST LOW (o)
- Powell et al. (2003) −∙−−∙
- Donelan et al. (2004) −−∙−∙−

- CBLAST Data
**LF (****◊****)****    RF (****□****)**
**LR (X)    RR(****+)**

## Dalton Numbers

**C****E10N**** = <w'q'>/U****10N****(q****sat****-q****10N****)**

## Stanton Numbers

**Δ****  CBLAST **
** ****X   HEXOS**

## CK/CD = 0.63 < 0.75

- -------- COARE 3.0
- -------- Emanuel’s threshold

- CK/CD = 0.63 < 0.75

**Δ****  CBLAST **
** ****X   HEXOS**

*Zhang, Black, French and Drennan, 2008: *First direct measurements of enthalpy flux in the hurricane boundary layer: the CBLAST results. *Geophys. Res. Lett.*, **35,** L14813, oi:10.1029/2008GL034374.

## Fk (W m-2)

- Fk (W m-2)

- u* (m s-1)

- Cdx1000

- Ckx1000

## Vertical Structure of Momentum flux 

- –— Moss (1978)

**Notes:**
Emphasize the difference. 

## Profiles of humidity and sensible heat fluxes

## TKE Budget

- I :  Shear production
- II:  Buoyancy
- III: Turbulent transport
- IV: Pressure transport
- V:  Rate of dissipation

-            I                               II                   III         IV       V

- TKE:

## Turbulent Kinetic Energy Budget

- Nicholls (1985)

- Lenschow et al. (1980)

- Zhang et al. 2009 JAS accepted

## Hurricane Boundary Layer Rolls

- Morrison et al., 2005

##  RADARSAT SAR imagery

-  RADARSAT SAR imagery
- during Hurricane Isidore

- Zhang et al. 2008 BLM

##  Boundary Layer Flight in Hurricane Isidore

## Wavelet Analysis

## Momentum Flux

- ----- alongwind leg
- ─── crosswind leg

- Wavelength ~ 950 m

- ───  leg A
-  ---------  legs B C D
-               leg E

- Zhang et al. 2008 BLM

## Sensible Heat Flux

- ───  leg A
-  ---------  legs B C D
-               leg E

- Zhang et al. 2008 BLM

## Hurricane Hugo (1989)

- Marks et al. 2008 MWR

## A schematic of the hurricane boundary layer height 

- rmw

- re

**r**

- z

- hi

- θ

- Vr

- A schematic of the hurricane boundary layer height

- Vr=0

- Vr= -10 m s-1

- r=150 km

- h

- hinflow

- zi

- Eye radius

- Max wind radius

- Mean Wind Speed Profiles

- WL150 is the mean wind of the lowest 150 m data

- Height of maximum wind speed

## Mean Potential Temperature Profiles 

- Mean Potential Temperature Profiles

**Stable layer**
**Transition Layer**
**Mixed Layer**

- mixed layer height **z****i**

**Δθ**** (z****i****) ~ 1K**

- Mean Radial Wind Profiles

- Inflow layer height Vr = 0

## ?

- rmw

- re

- r

- z

- Vr=0

- hinflow

- r=150 km

**Entrainment ?**

- r=500 km

- zi

- Eye radius

- Max wind radius

- Where is the top of the hurricane boundary layer?

- hVmax

- 800 Wm-2

## Summary

- 2. The vertical structure of turbulence and fluxes are presented for the boundary layer between the outer rainbands.
- The boundary layer height defined from the turbulent flux profiles is nearly twice the height of the mixed layer defined from the thermodynamic profiles.
- Turbulent kinetic energy budget indicates that the advection term is important.
- Boundary layer rolls rescale the sensible heat flux transport and enhance the momentum flux.

## Future Possible Hurricane Boundary Layer Turbulence and flux Observations

- P3 aircraft flying low again?
- GPS dropsonde
- Remote sensing (Radar, Lidar, etc.)
- Aerosonde with turbulence instrumentation
-  Buoy designed to sustain hurricane force

## End

- Thanks!

## Hurricane boundary layer depth

- Deardorff (1972) :  zi = c u*/f
- Anthes and Chang (1978) :
-               zi =
- Kepert (2001) :

- is Inertial instability parameter* *

- Consistent with Anthes and Chang (1978) and Kepert (2001)