# Presentation: 559450

## Mobile Ground-Based Observations of Landfalling Hurricanes: Current Capabilities and Future Plans

- Kevin Knupp, Walt Peterson and Dan Cecil
- Department of Atmospheric Science
- and
- Earth System Science Center
- University of Alabama in Huntsville

## Outline

- Goals (previous deployments)
- Instruments
- Past research activities – some highlights
- Future research possibilities

## General Research Goals

- _Topics that have been considered at least superficially_
- Atmospheric Boundary Layer (ABL) Processes
**ABL transition**: land-to-water and water-to-land
**Wind profiles**
- Structure of ABL eddies, damaging wind streaks, etc.
**Intensity change** around the landfall time
- What factors, such as **cold air production** over land, control intensity?
- _Topics not yet addressed_
- QPE (radar) and raindrop size distribution variability
- Horizontal and vertical variability; factors controlling variability
- Related mesoscale phenomena
- Rainband/stratiform region kinematics and vertical transports
- Tornadoes, gravity waves, fronts (and their interaction)

## UAH deployments to date

**Hurricane Earl (1998),** Tallahassee, FL
- 	Adjacent to TLH WSR-88D, east of circulation center
**Hurricane Georges (1998),** N of Gulfport, MS
- 	Close to two DOW radars, remained within west eyewall for several hours
- Hurricane Irene (1999), NC
- 	Irene turned to the right; no landfall
- Tropical Storm Helene (2000), Panama City, FL
- 	Modest rain, east of circulation center
**Tropical Storm (Hurricane) Gabrielle (2001),** Venice, FL
- 	Center passed over MIPS, co-located with SMART-R
- Hurricane (Tropical Storm) Isidore (2003), Gulfport, MS
- 	Sampled the right side, co-located with TTU towers and SMART-R
**Hurricane Ivan (2004),** 5 km N of Orange Beach, AL
- Sampled right eyewall, co-located with DOW

## Instrumentation

***Mobile Integrated Profiling System (MIPS)***
- 915 MHz Doppler wind profiler
- X-band Profiling Radar (under construction)
- 12-channel microwave profiling radiometer
- Lidar ceilometer
- Surface instrumentation

***Mobile Meteorological Measurement Vehicle (M******3******V)***
- Surface measurements

***Mobile Alabama X-band (MAX) radar***
- Dual polarization capability
- Under construction, will be ready for the 2007 season.

- Future

## Components of the Mobile Integrated Profiling System (MIPS)

- Components of the _**M**_obile _**I**_ntegrated _**P**_rofiling _**S**_ystem (MIPS)
- 1)  915 MHz Doppler wind profiler
- 2)  12 channel microwave profiling radiometer
- 3)  Lidar Ceilometer
-  Doppler sodar
-  Electric field mill
-  Surface instrumentation
- 7)  Satellite communication
- 8)  Parcival disdrometers (new, not shown)

- Future:  X-band Profiling Radar (XPR) will replace the sodar

- _[http://vortex.nsstc.uah.edu/mips](http://vortex.nsstc.uah.edu/mips)_

**1**

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**5**

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**7**

## An ideal MIPS location on 23 June 2003 (BAMEX)

- 3. Mobile Meteorological Measurement Vehicle
- (M3V)

- MIPS van and instrument trailer

- 2. Pickup & power trailer

- 6/23/03

## Past research topics

- Examination of wind profiles and their variability
- Boundary layer properties
- Fronts – in hurricanes? – yes
- Cooling over land can be prominent and important
- Cool air + convergence can produce frontogenesis
- Intensity change?
- Gravity waves
- Prominence (Gabrielle)
- A noteworthy gravity wave event in Hurricane Earl
- The most active weather was associated with a gravity wave
- Impact – unknown

## Analysis of TS Gabrielle (NASA CAMEX-4 campaign)

**Boundary layer transition** for both on-shore and off-shore flow.  (The circulation center passed very close to the MIPS)
- Generation of **shallow warm and cold fronts**
**Production of cold air** over land

*Leading*

*Rainband*

**x**

- Intense deep convection

- Reflectivity from Tampa Bay WSR-88D

***MIPS & SMART-R***

## 915 MHz 

- 915 MHz
- profiler moments

- Regions in terms of precipitation characteristics:

- Leading stratiform
- Convective region
- Inner core region
- West flank stratiform

- Flow regimes

- Off-shore:  0400-1100 UTC
- On-shore:  after 1200 UTC

- The stable off-shore regime does not exhibit enhanced spectral width, but the on-shore regime does.

- Core

## 915 MHz wind profiles at 30 min intervals

- off-shore, veering with height
- cool surface air, stable BL

- on-shore, backing with height
- warmer surface air, neutral to stable ABL

***TS Gabrielle***

## Surface fluxes produced from cool air flowing over warm water  production of temperature gradient along the coastal waters

- coastline

*land*

*water*

- Cool air, 22 C

- Warm water, 28 C

- Surface fluxes

*Off-shore flow*

**Spatial variability across the coastal zone**

- MIPS
- profile

*Isotachs (m s**-1**)*

- Descending jet

- Analysis based on Doppler radar + profiler

## Spatial variability across the coastal zone

- Flow deceleration is apparent at flow levels over land.
- Flow deceleration begins over water, prior to air reaching the land surface.  Implication: perturbation pressure gradient force from dynamic forcing.
- BL height is not well defined by the isotachs.
- Vertical shear above the jet over water is greater than that over land.

**Near surface winds are slowed by increase in surface roughness**

## Temporal variability in the 915 MHz wind profiles, 1330-1430 UTC

- Systematic wind variation during this period:
- Rapid changes in the wind profile close to the core region
- General backing below 1 km
- Sharp backing of wind with height is large initially.
- Wind speed profile evolves from maximum at 200 m to a jet profile in which the maximum ascends with time.  Thus, the jet is initially within the turbulent BL (consistent with Kepert 2001).

*Jet location near the surface*

## Fronts

- 0553

- 0553

- 0853

- Cool air (T≤23 C) covers a large area (50,000 km2).
- Stratiform rainfall is widespread downshear of the core of Gabrielle.
- A warm front formed as Gabrielle approached.  This front was associated with tornadoes near 0800 UTC

- Surface Analysis

- MIPS
- location

***Fronts***

***Cool air**** *

***Tornadoes formed along a warm front***

## Surface Analysis

- 1153

- 1453

- A cold front appeared after 1200 UTC; occlusion by 1453 UTC.
- The fronts were shallow, confined to the ABL.
- The strongest frontal signature occurred at the MIPS site (near the center of the storm)

***Cold front***

***Fronts***

## With regard to cold air production over land, the observations suggest the following hypothesis:

## Hypothesis: Landfalling hurricanes weaken at an accelerated rate upon ingesting cold (low-valued e) continental air from the ABL

- The presence of **cold air within the ABL will produce a rapid weakening** in the storm if entrained into the core region.
- The cold air is produced by **rainfall evaporation within mesoscale downdrafts** whose characteristics (relative distribution relative to the center, minimum e) are predictable.
- This hypothesis is consistent with observed rapid weakening over cool water.  In fact, the weakening from cold air intrusion may be even more dramatic.

## Cooling within stratiform precipitation

**Cooling within stratiform precipitation**
**Significant mesoscale downdrafts provided downward transport of low-valued ********e**** air, and thereby produced appreciable cooling at low levels.**

*w derived from EVAD analyses*

- Gabrielle

## Is this process observed in other storms?The case of Ivan:Cold air from the continent may have produced weakening in the NW flank just before landfall

## Surface 0043 16 September 2004

- Cold feeder flow
- e = 343 K

- Extensive stratiform precipitation is present to the north of the circ center.

- Ivan appeared to weaken rapidly around the time of landfall, more so than was forecast.

## Future work in this area:

- Further examine the “cold air” hypothesis.
- Relate the production of cold air to:
- Thermodynamic vertical profiles in advance of the hurricane
- Rainband kinematics, i.e., a more detailed description of the mesoscale downdrafts within rainbands and stratiform precipitation
- Precipitation properties

## Future plans

- More of the same, plus:
- QPE (Quantitative Precipitation Estimation)
- Disdrometers  profiler  radar calibration and improved Z-R (and eventually polarimetric) relations
- Improved real-time QPE with the WSR-88D network
- Precipitation growth processes (and drop breakup)
- Mesoscale dynamics
- Rainband and stratiform kinematics
- Inner core processes
- Thermodynamics – cooling within stratiform precipitation

## Rainband Kinematics:

**Rainband Kinematics:**
-    A future research thrust
- Kinematic structure of rainbands in TS Gabrielle (dual Doppler analysis using SMART-R and TBW WSR-88D)

- Peak values of updrafts and reflectivity in the rainband :
-  20 m s-1 and >50 dBZ

- Vertical E-W section

***TS Gabrielle***

## Raindrop spectrum and size distributions 

**Convolved distribution**

**Observed distribution**

**Hydrometeor size distribution**** **

- Raindrop spectrum and size distributions

**Time: 060226 UTC  Ht : 3.578km  Vobs: 8.06m/s  D****m****: 1.67mm  Spectral width: 2.52m/s   ******** = 3**

*Doppler spectra*

*Size distributions*

- Develop a better understanding of precipitation processes, and drop break-up in the turbulent boundary layer.

## Summary

- Mobile instruments have been used to examine:
- Flow transition within the ABL across the coastal zone
- Gravity waves in the hurricane environment
- Cold air production over land, which appears to exert a large impact on hurricane intensity around the time of landfall
- Future work should continue to investigate the above plus
- Investigations of rainband & stratiform kinematics and thermodynamics
- Precipitation physics and improved Z-R relations for accurate QPE, with applications to the future dual-pol capability of the WSR-88D

## But, this will require a dedicated multi-year field campaign utilizing other resources

- WC-130

- NOAA P-3 (2)

- In situ, dropsondes, radar

- In situ, Dropsondes
- Radars, Cloud physics

- radar

- Doppler radar

- Atmospheric & BL profiling
- (wind, T, v, cloud, precipitation)

- Mobile Doppler radars

- Towers
- (~10)

## Questions?

- E-mail:  _[kevin@nsstc.uah.edu](mailto:kevin@nsstc.uah.edu)_
- Web site: _[http://vortex.nsstc.uah.edu/mips](http://vortex.nsstc.uah.edu/mips)_

## Hurricane Earl (1998)

- Cold air at the surface can provide an environment conducive to gravity waves
- Doppler profiler observations of a gravity wave associated with Hurricane Earl at landfall (M.S. thesis by Barry Roberts)

## Combined analysis

**Combined analysis**
- Maximum updraft and downdraft of +13 and -9 m s-1 near the 0.8 km AGL level
- Low uniform cloud base within the updraft

## FutureX-band Profiling Radar (XPR)

- 9.4 GHz ( = 3.3 cm)
- Peak power: 50 kW
- Min detectable Z at 4 km: -20 dBZ
- Time resolution 1-20 s
- PRF ~ 2500 s-1
- Minimum gate spacing: ~30 m
- Profiles of Z, W, Doppler spectra
- Precipitation & clouds
- Boundary Layer Properties

**915**

**XPR**

## Surface instrumentation

- T
- RH
- p
- Wind
- Solar radiation
- Rainfall rate
- Electric field
- DSD (Parcival optical disdrometers)

## Conclusions (ABL transition)

- Significant temporal variability in airflow at the MIPS site related to gravity waves, large eddies (and boundaries).
- Stable off-shore flow exhibited a jet profile that descended from land to water.  Wind shear below the jet decreased over water.
- On shore flow produced a more unstable BL.
- In both cases, flow adjustment within the BL occurred  within about 5 km of the coast line
- A transition in flow occurs in the onshore (off-shore) cases as deceleration (acceleration) is observed to occur before air passes over the coast line.