Category Archives: Atmospheric Physics

ToPROF: Ceilometers and Lidar Applications

 As part of the EU “COST” programmes,  the ToPROF group is working on  operational ground based profiling with ceilometers, doppler lidars and microwave radiometers for improving weather forecasts.
Work started in 2014,  and is progressing towards a nominal completion date in 2020.
For overall details refer to the ToPROF Home Page
Within the To PROF group,  a Ceilometer Working group has been established.
Here are the details of this working group  This group would be of interest to  those within the following End-Users
  • National weather services (incl. COPERNICUS/MACC): calibrated attenuated
    backscatter profiles to evaluate NWP models (through forward operators); Cloud
    base height for NWP evaluation and weather monitoring.
  • Agencies in charge of atmospheric surveillance for air traffic: occurrence, height and  mass concentrations of ash layers; diagnostic and short-term forecast of fog and other low visibility events.
  • Agencies in charge of Air Quality monitoring: boundary layer height; freetropospheric aerosol transport.
  • Networks in charge of GHG monitoring: boundary layer height to quantify GHG
    dilution effects.
  • EUMETSAT: European-wide validation of cloud-base height and fog
  • Renewable energy industry: Photovoltaic ReN – cloud/fog fraction and evolution for nowcasting applications (combined with geostationary satellite); Concentrated solar power: aerosol vertical distribution; Wind ReN – wind profiles from Doppler Lidars.
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International Commission on Clouds and Precipitation (ICCP)

The International Commission on Clouds and Precipitation (ICCP) is a Commission of the International Association of Meteorology and Atmospheric Sciences (IAMAS)
The IAMAS is one of the associations of the International Union of Geodesy and Geophysics (IUGG)

The ICCP holds a conference every 4 years.   The last conference was at Manchester University in 2016, The next is due in 2020.

Typical subjects in calls for papers are theoretical, observational and numerical modelling studies of cloud and precipitation physics, cloud chemistry and cloud dynamics.  

For instance the following subjects are commonly covered at the conferences

  • Basic cloud and precipitation physics
  • Warm boundary layer clouds
  • Convective clouds (including cloud electrification)
  • Mixed phase clouds (including Arctic/Antarctic stratus, mid-level clouds)
  • Cirrus clouds
  • Orographic clouds
  • Fog and fog layers
  • Mesoscale cloud systems (including severe storms)
  • Tropical clouds
  • Southern Ocean clouds
  • Polar stratospheric clouds and noctilucent clouds
  • Aerosol-cloud-precipitation-interactions and processing
  • Clouds and climate (including radiative properties of clouds)
  • Ice nuclei and cloud condensation nuclei
  • Cloud and precipitation chemistry
  • Measurement techniques (of cloud and precipitation properties) and uncertainties
  • Applications of cloud and precipitation physics

Ceilometers and Snow

Like Rain, Snow produces quite high levels of backscatter.   But the raindrops and snow flakes have very different shapes, velocities and surface area to mass ratios.  More expensive ceilometers may have the ability to discriminate between snow and rain.

A typical LIDAR curtain plot for cloud appears below:

snow plot

Ref: University of Utah Atmospheric Science

The snow is coming from a cloud at around 500m .  The cloud and snow appear to extinguish the returns from higher layers,  if any.   Some of the snow is light and evaporates before it gets to ground level.  ( low level green return )

Work has been done to try to determine snowfall rate from Lidar returns.  According to Ed Eloranta of the University of Wisconsin Madison,  the technique requires radar and  does not require any knowledge of the snowflake shape.

Download Poster

http://lidar.ssec.wisc.edu/papers/conferences/arm2009/arm_09.pdf

 

 

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.

Cloud Atlas

The definitive reference to cloud types and Cloud species is the ICAO Cloud Atlas which can be downloaded for free from this site:

WMO Cloud Atlas Vol 1    WMO Cloud Atlas Vol 2

There are a number of less detailed cloud type images on the internet.   For example

Clouds Online

The Australian Bureau of Meteorology have a good references to cloud observation

Australian Bureau Chapter 13

Cloud Types Graphic

Current ceilometers have a range out to about 25,000 ft,  and other models with larger telescopes built in,.  can reach up to about 40000 ft.   For use in aviation,  at airports a range of 12,00 ft is considered adequate.