Tag Archives: Ceilometer

New WMO Cloud Atlas

The WMO has released a new Cloud Atlas.  The release was timed to coincide with the World Meteorological day.    23/3/2017

Here is the Press Release

 

Here is the Home page for the new Cloud Atlas.

 

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Ceilometers for Dust Storm Profiling

Sydney Dust Storm 2009

A wall of dust stretched from northern Queensland to the southern tip of eastern Australia on the morning of September 23, 2009, The storm, the worst in 70 years, led to cancelled or delayed flights, traffic problems, and health issues,  The concentration of particles in the air reached 15,000 micrograms per cubic meter in New South Wales during the storm, A normal day sees a particle concentration 10-20 micrograms per cubic meter.

Work on the use of Ceilometers for analysis of  that  Dust Storm is decribed in the paper:

Laser ceilometer measurements of Australian dust storm highlight need for reassessment of atmospheric dust plume loads      By Hamish McGowan and Joshua Soderholm

Among the more interesting information in this paper was the curtain plot showing the increase  in backscatter when the wall of the duststorm hit,  the very high concentration around ground level and the vertical extent of the dust.  The maximum vertical extent of this plot is 1500 metres ,  or approx 5000 ft.

dust-storm

(Curtain Plot showing onset of the Dust Storm and estimated particle Concentration from paper: Laser ceilometer measurements of Australian dust storm highlight need for reassessment of atmospheric dust plume loads      By Hamish McGowan and Joshua Soderholm )

Ceilometers like the 8200-CHS are suitable for this type of work,  where dust storms are experienced regularly,  such as the Harmattan in sub saharan Africa,  the Churgui in Morocco,  the Khamasin in Egypt, the Shamal in Iraq or the Kali Andhi in India

High Altitude Clouds

High Altitude clouds  fall into 2 categories,

  1. Those with  a low base and vertical development are Cumulonimbus and Towering Cumulus.     At the base these are water clouds,    so the ceilometer only “sees”  a few hundred feet into the cloud.
  2. Those with a high base,  including Cirrus, Cirrostratus and Cirrocumulus and Altostratus

The Cirrus cloud family are composed of Ice Crystals,  and are very often “optically thin”and they have low backscatter coefficients,  so are difficult to detect with ceilometers,  because the laser pulse energy is limited to eye safe levels.

Altostratus may be composed of ice crystals. In some ice crystal altostratus, very thin, rapidly disappearing horizontal sheets of water droplets appear at random. The sizes of the ice crystals in the cloud tended to increase as altitude decreased. However, close to the bottom of the cloud, the particles decreased in size again

Altostratus cloud with a water phase  may have a strong backscatter signal and can be picked up as in the case below

17000 FT 26-11 TREVISO

Alto stratus Cloud at 17,000 ft

Ref 1 : Wikipedia : Alto Stratus entry.

Ref 2.  Wikipedia Cirrus Cloud entry.