Cloud microphysics and precipitation through the eyes of

METEOSAT SECOND GENERATION (MSG)

Thomas HeinemannMeteorological Products Expert

Thomas.Heinemann@eumetsat.int

www.eumetsat.int

Contributors: J. Kerkmann(EUM), D. Rosenfeld (HUJ), J. Prieto (EUM)

7. Cloud Particle Size

Picture from Bob White

Observing Cloud Particle Size

MFG: not possible ( only cloud thickness and cloud top temperature)

MSG: possible ( 2 NIR window channels)

• NIR1.6 and IR3.9 channels (day)• IR3.9 - IR10.8 BTD (day & night (warm clouds))

• IR8.7 – IR10.8

• Reflection at NIR1.6 and IR3.9 is sensitive to cloud phase and very sensitive to particle size

• Higher reflection from water droplets than from ice particles

• During daytime, clouds with small water droplets (St, Sc) are much brighter than ice clouds(non-inverted image)

Reflection of Solar Radiation

MSG-15 June 200314:45 UTCChannel 03(1.6 m)

Small ice particles(40-50%)

Large ice particles(30%)

Channel 03 (NIR1.6): Cloud

Particle SizeWater clouds

(50-70%)

MSG-1, 20 May 2003, 13:30 UTC

Channel 04 (IR3.9) Channel 09 (IR10.8)

Channel 04 (IR3.9): Cloud Particle Size

1 1

1= ice clouds with very small particles2= ice clouds with small particles3= ice clouds with large ice particles

31 1

1

3

3

1

1

1

3

3

3

2 2

IR3.9 shows much more cloud top structures than IR10.8 (very sensitive to particle size)

REFL = 100 * (R_tot - R_therm) / (TOARAD - R_therm)

with:

REFL Reflectance [in %] for channel IR3.9

R_tot measured total Radiance [in mW m-2 ster-1 (cm-1)-1] for channel IR3.9

R_therm CO2-corrected, thermal component of Radiance [in mW m-2 ster-1 (cm-1)-1]

for channel IR3.9

TOARAD CO2-corrected, solar constant at Top of the Atmosphere [in mW m-2 ster-1 (cm-1)-1]

for channel IR3.9

R_therm = R(IR3.9, BT(IR10.8)) * R3.9_corr

Estimation of IR3.9r

Channel 04r (IR3.9r): Cloud Particle Size

Maputo

MSG-1, 6 November 2004, 12:00 UTC, Channel 04r (IR3.9r)Range: 0 % (black) to +60 % (white), Gamma = 2.5

Large Ice Particles(1/2%)

Small Ice Particles(8/11%)

Water Clouds (20/25%)

Water Clouds(16/20%)

Difference IR3.9 - IR10.8: Cloud Particle Size

Maputo

MSG-1, 6 November 2004, 12:00 UTC, Difference IR3.9 - IR10.8Range: -5 K (black) to +70 K (white), Gamma = 0.5

Large Ice Particles(+26/+35 K)

Small Ice Particles(+65/+73 K)

RGB VIS0.8, IR3.9r, IR10.8: Colour Inputs

Red Green

Blue RGB

Maputo

MSG-1, 6 November 2004, 12:00 UTC, RGB VIS0.8, IR3.9r, IR10.8

Thin Ice Cloud (small ice)

Thick Ice Cloud(small ice)

Thick Ice Cloud(large ice)

Thin Ice Cloud (large ice)

Particle Size seen in Microphysical RGB

Deep precipitating cloud(precip. not necessarily reaching the ground)

- bright, thick- large ice particles- cold cloud

Deep precipitating cloud(Cb cloud with strongupdrafts and severeweather)*

- bright, thick- small ice particles- cold cloud

*or thick, high-level lee cloudiness with small ice particles

Thin Cirrus cloud

(large ice particles)

Thin Cirrus cloud

(small ice particles)

Ocean Veg. Land Fires / Desert Snow

Colour Interpretation

Comparison RGB 02,04r,09 vs Channel IR10.8

MSG-1 7 September 2003, 11:45 UTC

12

3

1. Large thin ice (dissipating storm)2. Large thick ice 3. Small thick ice (developing storm)

RGB 02, 04r ,09 Channel 09 (IR10.8)

MSG-17 September 200311:45 UTCRGB CompositeRed = VIS0.8Green = IR3.9rBlue = IR10.8

Animation (1/3)

MSG-17 September 200312:00 UTCRGB CompositeRed = VIS0.8Green = IR3.9rBlue = IR10.8

Animation (2/3)

MSG-17 September 200312:15 UTCRGB CompositeRed = VIS0.8Green = IR3.9rBlue = IR10.8

Animation (3/3)

Estimation of Cloud Drop Effective Radius (Re)

Reflectance at 3.9 m decreases with increasing Re,and saturates at about Re > 40 m (depending on instrument noise) !

• Re is calculated from IR3.9r, using look-up table with viewing geometry as inputs

• only for thick clouds that pass the following criteria:

Refl. VIS0.6 > 0.5 BT(IR10.8) < 290 K -0.5 K < BTD IR10.8 - IR12.0 < 1.5 K -1.0 K < IR10.8 - IR8.7 < 5.0 K

The T versus Re Scatterplot (Rosenfeld, Lensky, 1998)

MSG-1, 20 May 2003, 13:30 UTC

1) Define a window containing a convective cloud cluster with elements representing all growing stages typically containing several thousand pixels

The T versus Re Scatterplot (Rosenfeld, Lensky, 1998)

1) Define a window containing a convective cloud cluster with elements representing all growing stages typically containing several thousand pixels

2) Calculate T (top temperature from IR12.0 channel) and Re (from IR3.9 channel)

MSG-1, 20 May 2003, 13:30 UTC

The T versus Re Scatterplot (Rosenfeld, Lensky, 1998)

1) Define a window containing a convective cloud cluster with elements representing all growing stages typically containing several thousand pixels

2) Calculate T (top temperature from IR12.0 channel) and Re (from IR3.9 channel)

3) Calculate the median and other percentiles of the Re for each 1°C interval of cloud top temperature

The T versus Re Scatterplot (Rosenfeld, Lensky, 1998)

1) Define a window containing a convective cloud cluster with elements representing all growing stages typically containing several thousand pixels

2) Calculate T (top temperature from IR12.0 channel) and Re (from IR3.9 channel)

3) Calculate the median and other percentiles of the Re for each 1°C interval of cloud-top temperature

4) Display graphically the T versus Re curves of the 5th, 10th, 25th, 50th, 75th, 90th and 95th percentiles

The T versus Re Scatterplot (Rosenfeld, Lensky, 1998)

1) Define a window containing a convective cloud cluster with elements representing all growing stages typically containing several thousand pixels

2) Calculate T (top temperature from IR12.0 channel) and Re (from IR3.9 channel)

3) Calculate the median and other percentiles of the Re for each 1°C interval of cloud-top temperature

4) Display graphically the T versus Re curves of the 5th, 10th, 25th, 50th, 75th, 90th and 95th percentiles

5) Analyse the shape of the median (50th percentile, in green colour) to find the microphysical zones (see next slide)

The Microphysical Zones

Mixed Phase Zone

Droplet CoalescenceGrowth Zone

(Diffusional DropletGrowth Zone)

Glaciated Zone

Mixed Phase Zone

Droplet Coalescence Growth Zone

Glaciated Zone

Rainout Zone

Source: Rosenfeld & Lensky (1998)

NOAA, AVHRR composite image14 December 1997, 06:23 UTC

The Microphysical Zones

1. The Time Space Exchangeability (Ergodicity)

Lensky & Rosenfeld (2005):

“The T -Re relations of a convective cloud field is stable over time, and depends mainly on the thermodynamic and aerosol properties of the air mass”!

Some Important Properties of the T - Re Relation

2. The Increase of Re with Height

Lensky & Rosenfeld (2005):

“The effective radius of convective clouds increases with height:”

- Slower with in more polluted air mass- Slower with faster updraft velocities

Some Important Properties of the T - Re Relation

3. Re for Severe Convective Storms

Lensky & Rosenfeld (2005):

“Severe convective storms are characterized by small effective radius reaching very cold temperatures!”

Some Important Properties of the T - Re Relation

Typical T-Re Scatterplots for different Updraft Velocities

weak tonormal

strong very strong

1

2

3 4

5

6

MSG 2003 05 20 12:42 2_4r(g=2)_9

MSG 2003 06 05 14:57 2_4r(g=2)_9

1

23 4

5

MSG 2003 05 20 13:42 2_4r(g=2)_9

Hailstorm Potchefstroom: 27 Oct 2004

SmallSmall LargeLarge

NIR1.6 high Refl. (40-50%) low Refl. (30%)

IR3.9r high Refl. (5-10%) low Refl. (1-2%)

IR3.9 - IR10.8 large pos. (40-75 K) pos. (20-30 K)

Microphys. RGB

Convection RGB

Summary (for thick, cold ice clouds, day)

SmallSmall LargeLarge

NIR1.6 N/A N/A

IR3.9r N/A N/A

IR3.9 - IR10.8 strongly influenced by IR3.9 noise

Microphys. RGB N/A N/A

Convection RGB N/A N/A

Summary (for thick, cold ice clouds, night)