# Cloud Microphysics - Does It contain Ice Or Water Or Both?

I'm not sure if this is the right site to post this on but I have a project where I have some cloud microphysical properties:

Altitude, Pressure, Temperature, Effective Radius,
Liquid Water Content, Particle Number Concentration


I need to use this data to work out whether the cloud contains water, ice or a mixture of both. Also if possible work out what type of cloud it is.

How should I go about doing this? Are there any good datasets I should know about that would help?

The end product will be an algorithm where you give it the data above and it tells you the cloud type and contents.

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Your problem is underdetermined. Frozen water can occur at T<0°C, but supercooled water can occur at temperatures down to -30°C. Particles freeze heterogeneously (i.e. on top of a cloud condensation nuclei (CCN)) at temperatures quite low to zero, but if the concentration of CCNs is very low, there is no way to determine the ratio between frozen and liquid water from the data you mention. The only thing you can know more or less for sure is:

• $T>0°C$ — cloud contains only liquid
• $0>T>-15°C$ — cloud is mostly liquid
• $-15°C>T>-40°C$ — cloud contains both
• $T<-40°C$ — cloud contains only ice

For example see this page, that mostly corresponds to what I know otherwise. There exist techniques to determine the phase for particles through remote sensing, but they are still underconstrained. If you know the particle sizes (which, in the real world, you don't) and mass and number concentrations (which you can't remotely determine independently, either), you could use lidar and radar to further constrain the problem.

A lot of literature has been written on the subject.

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What about when $T>0°C$ but $P << P_{atm}$? –  Pranav Hosangadi Oct 31 '13 at 5:01
@PranavHosangadi There are no water clouds in the region where that occurs. –  gerrit Oct 31 '13 at 10:42

If you have the effective radius it's relatively simple to determine what levels of water or ice is contained within a cloud, as they have different wavelength absorption characteristics.

The British Atmospheric Data Centre has a huge dataset list here.

Here's an example of a research team who have done something similar to what you have outlined, but in order to find the ice/liquid water content of (specifically) cirrus clouds, based on radar reflectivity measurements.

Or try this report from Oxford University for a more complete algorithm covering different cloud types, using ATSR-2 data which might be more applicable to you.

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Could you expand on the first part? I have the effective radius but no absorption data. –  Ed0906 Oct 30 '13 at 18:22
Well the effective radius usually increases as water moves from a liquid to ice phase, so going by effective radius would probably be a bit more reliable than just using temperature data, as otherwise you run into the supercooling problem illustrated by gerrit below! However ice crystal shapes can be irregular so this is not always accurate. Alternately if you have LWC and total water content you can subtract to find IWC. The only problem there is that some datasets don't really differentiate between LWC and total water content. –  wingsofvalmar Oct 31 '13 at 15:48
Thanks, that cleared it up a bit. I have a feeling my dataset is one that does not distinguish between LWC and total water content (I calculate LWC from particle concentrations for various discrete particle sizes using summation instead of an integral). –  Ed0906 Oct 31 '13 at 18:18