Hurricane cloud physics
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Hurricane Cloud Physics. Robert A. Black NOAA/AOML/HRD. Main Research Topics . Rainfall and the warm rain process Precipitation Chemistry Aerosols Ice microphysics Lightning Ice particle nucleation Bergeron Process precipitation growth. How to get rain from vapor.

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Hurricane Cloud Physics

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Hurricane cloud physics

Hurricane Cloud Physics

Robert A. Black

NOAA/AOML/HRD


Main research topics

Main Research Topics

  • Rainfall and the warm rain process

  • Precipitation Chemistry

  • Aerosols

  • Ice microphysics

    • Lightning

    • Ice particle nucleation

    • Bergeron Process precipitation growth


How to get rain from vapor

How to get rain from vapor

  • Hygroscopic particles (CCN)

  • Absorb water from vapor to provide droplets

  • Problem - This process narrows the size distribution

Köhler Curves


Collision coalescence

Collision-Coalescence

  • Fortunate larger droplets fall faster, collide, & stick together to form ever larger drops

  • Numerical simulations show raindrop formation in 25-30 min.


Bergeron process

Bergeron Process

  • Ice particles grow at the expense of (supercooled) cloud

  • These get large enough to fall out, melt, & produce rain


Ice crystal morphology

Ice Crystal Morphology

  • Ice crystal shape is governed by the temperature and saturation ratio.

  • Above the black line, the air is supersaturated with respect to water

  • Below it is ice saturation only.


Where does all the ice originate

Where does all the ice originate?

Graupel

  • Ice nucleation is very inefficient at T > -15ºC

  • Hallett & Mossup, (1974) Provided the clue

  • -3ºC > T > -8ºC, growing graupel ejects numerous ice splinters, the “ice multiplication” mechanism.


Instruments

Instruments

  • Aircraft-mounted

  • Particle Imaging Probes DMT CCP shown.

  • Doppler Radar

  • Analog measurement devices (T, P, RH, LWC)


Instruments cont

Instruments - Cont.

  • Aircraft-mounted

  • DMT PIP Probe (top)

  • Measures precipitation 0.1 - 6.4 mm diameter

  • DMT CAPS Probe (Bottom) includes aerosols and cloud drops 0.1 - 50µm


Lwc 100

LWC-100

  • A “Hot wire”

  • Cloud water

  • Meter, measures

  • 0 - 5 g m-3 LWC,

  • Sensitive to drops

  • 50 µm

  • Next, a few images from hurricanes


Pms 2d c images 50 m res

PMS 2D-C images 50µm Res.

1.6 mm


Pms 2d c images 50 m res1

PMS 2D-C images 50µm Res.


Pms 2d c images 50 m res2

PMS 2D-C images 50µm Res.


Pms 2d p images 200 m res

PMS 2D-P images 200µm Res.


Pms 2dg p images 150 m res

PMS 2DG-P Images 150 µm Res.

9.6 mm

Some very large drops. (9.6 mm between white lines)


Pms 2dg c images 30 m res

PMS 2DG-C images 30µm Res.

1.92 mm


Pms 2dg p images 150 m res1

PMS 2DG-P images 150µm Res.


Pms 2dg c images 30 m res1

PMS 2DG-C images 30µm Res.


Pms 2dg p images 150 m res2

PMS 2DG-P images 150µm Res.


Platform limitations

Platform Limitations

  • WP-3D maximum altitude too low (-8ºC), or about 25K ft. (+6 hrs into flight)

  • Jets won’t fly below 35K ft (-40ºC).

  • Microphysically important -10ºC to -20ºC is unreachable.

  • A/C safety precludes flying below 1.5 km in eyewall when in precipitation.

  • Aircraft and instruments subject to damage from ice particle impacts and lightning


What do hurricanes offer

What do hurricanes offer?

  • Strong horizontal wind, but not usually damaging turbulence

  • Long lifetime - often a week or more.

  • Moderate updraft

  • No hail or tornados

  • Usually, little or no lightning


Hurricane allen 5 aug 1980

Hurricane Allen 5 Aug. 1980

  • Strong Cat-4

  • First mission dedicated to ice microphysics

  • First circumnavigation above melting level

  • First documented eyewall replacement cycle

  • Provided the evidence that killed Project Stormfury


Hurricane irene 26 sept 1981

Hurricane Irene 26 Sept. 1981

  • First time for a circumnavigation in convection

  • Updraft maxima < 10 m/s

  • Cloud LWC < 0.5 g m-3

  • Precip. Conc. < 30 l-1

  • Peak 2D-C > 100 l-1


What purpose for the ice

What purpose for the ice?

  • Willoughby et al, 1984 suggested the ice, by spreading out radially around the storm and inducing downdraft, aided the creation of “convective rings” (the eyewall, in other words)

  • Microphysically, the ice saturates and stabilizes the storm environment, thereby suppressing other convection outside the eyewall.


Lightning

LIGHTNING


Lightning origins

Lightning Origins

  • Takahashi, 1978, Saunders et al, 1991, 1992, 1996 all showed that graupel, supercooled cloud water, and ice crystals are all necessary for charge separation.

  • These researchers differ greatly on the relative quantities of these particles that are necessary.

  • These are very difficult measurements to make in natural clouds. Hurricanes provide one good place to try.


Hurricane study

Hurricane Study

  • Black & Hallett, 1999

  • Measured Ez and Ey

  • 2-D particle imagery

  • No Cloud LWC

  • No cloud droplet measurements of any kind


Lightning in hurricanes cont

Lightning in Hurricanes - Cont.

  • Only convective areas were charged

  • Stratiform areas had little or no charge

  • Transition between areas with much liquid water and little ice to all ice and little water were abrupt.


Conceptual model

Conceptual model


Conclusions

Conclusions

After 30 years, there are still outstanding questions.

The vertical distribution of cloud water is unknown

The partitioning of the condensate mass between precipitating and non-precipitating particles, graupel, rain, and snow remains hard to quantify.

The relationship between updraft speed and all these particles at various altitudes is still uncertain

The influence of the SSA and other aerosols on the convection remains to be measured.

Lightning is a sign of stronger updraft - what is the relationship between flash rate, storm structure, and the microphysics that separates the charge?


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