Author Archives: Mike

Ceilometer Network detects Dust Plume

Title: Dust storm from Syria- a potential new aerosol source in the E. Mediterranean- A ceilometer and synoptic study
Authors: Alpert, Pinhas; Egert, Smadar; Uzan, Leenes

Abstract

On 7 Sep 2015 an unprecedented huge dust plume approached the SE Mediterranean basin from the northeast- Syria region. According to the Israeli meteorological service it is the first time in 75 years of measurements, that a dust storm reaches Israel early September, lasts several days and dust concentrations reach values 100 times the normal (1700µg/m3). Dust storms are normally monitored in the east Mediterranean using satellites and surface PM data. Obviously, these cannot show the vertical evolution of the dust including penetration, sinking and cleaning since vertical profiles are not available. High-resolution, micro Lidar Ceilometer network is gradually established in Israel. A few instruments of this network were already operational during the dust storm. The most crucial vertical information, monitored by these Ceilometers with 10m resolution vertically, every 16s, is analyzed. The difference in the cloud-layers allow the investigation of the high altitude of 1000m dust penetration, its sinking into the complex structured 250-500m mixed layer and the gradual 3D cleaning. This finding contradicts the conventional understanding that cleaning is due to gradual descent and shows not only the vertical fluctuation during the entire event but also the vertical rise to 2000m at the end of the event. The vertical information showed that the actual event period duration was 7 days, compared to only 90 hours based on traditional detectors. Is it a new dust source in the E. Mediterranean-long and short term trends?

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. Who supplies them ?

There are very few Ceilometer manufacturers in the world.   Ceilometers have advanced technical requirements and the cost of development is  high.   In the production phase ceilometers are assembled from  many special optical and electronic parts.   During testing they require specialised pulsed laser power meters,  spectrophotometers and advanced electronic test equipment, together with a cloudy climate to enable regular testing and continuous product improvement.

Sensor Range Class

  • 12500 ft range, ( 3800m)  an example of which was the original CT12K.  This range is now encompassed by the 25,000 ft range sensors.
  • 25,000 ft range ( 7600m) These are the main sensors on the market since  in the main application there is little operational need to go beyond even 12500 ft.  These sensors also find application in Planetary Boundary Layer ( PBL) studies.
  •  50,000 ft  range (15,200m) Special instruments that find more application in volcanic ash warning in aviation and upper atmosphere studies in atmospheric science.   Although in theory only requiring a modest increase in signal to noise ratio,  the cloud species above 20,000 ft are most often comprised of ice crystals and have much lower volume back-scatter coefficients than water cloud so the reliable detection of thin layers of cirrus cloud becomes very difficult while maintaining the laser eye safety mandate.  Ceilometers in this range generally achieve the necessary signal to noise ratio improvement by a range of techniques including increasing laser pulse energy ( while still remaining eye safe ), using a different laser wavelength,  and or reducing the telescope field of view and laser beam divergence.

25,000 ft range for Aviation and PBL studies

CL31     :  http://www.vaisala.com/en/products/ceilometers/Pages/default.aspx

8200-CHS :   http://www.ceilometers.com/

CS135   :   https://www.campbellsci.com.au/cs135

50000 ft Range for Atmospheric Science

CL51     : http://www.vaisala.com/en/products/ceilometers/Pages/default.aspx

8400-CHS    http://www.ceilometers.com/

 

 

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