observations of volcanic ash by lidar, modis and surface air-quality measurements robin hogan...

Observations of volcanic Observations of volcanic ash by lidar, MODIS and ash by lidar, MODIS and

surface air-quality surface air-quality measurementsmeasurements

Robin Hogan <[email protected]>University of Reading

Last updated: 18 April 2010

15 April: 1139 UTC15 April: 1139 UTC

NASA MODIS radiometer



Stationary colours in the sea (sediment and algae)

x Chilbolton

x CabauwVolcanic ash

Chilbolton Doppler lidar: 16 AprilChilbolton Doppler lidar: 16 April

Descending volcanic ash?

Vertical velocity shows turbulence in boundary layer and also in ash layer

Mixes into turbulent boundary layer

Background aerosol particles in the boundary layer (0-1 km)

Chilbolton Doppler lidar: 16 AprilChilbolton Doppler lidar: 16 April

Descending volcanic ash?

Mixes into turbulent boundary layer

Spherical liquid droplets have very low depolarization Ash is non-spherical

so strongly depolarizing

Background aerosol particles in the boundary layer (0-1 km)

Chilbolton Doppler lidar: Chilbolton Doppler lidar: 17 April17 April

• Further images at http://www.met.reading.ac.uk/radar/realtime/today.html

Normal aerosol particles in the boundary layer: no further sign of volcanic ash…

Surface sulphur Surface sulphur dioxidedioxide

Spike due to volcanic ash? Much less that UK air quality objective (1 hr average exceeds 350 g m-3 less than 24 times per year)

Aerosol particles Aerosol particles (PM10s)(PM10s)

Much less clear sign of ash

Possible ozone Possible ozone chemistry at chemistry at

Reading Reading (speculative!)(speculative!)

• Further data at http://www.airquality.co.uk/

Possible NO2 source due to volcano?

Converted to NO when sun comes up?NO2 + sunlight NO + O

Large ozone depletion: O3 + NO NO2 + O2

Ultraviolet EZ-lidar, Cardington Ultraviolet EZ-lidar, Cardington Bedfordshire, 16Bedfordshire, 16thth April April

• http://www.metoffice.gov.uk/corporate/pressoffice/2010/volcano/lidar/• This plot was produced by the University of Manchester, NCAS and FGAM.

RIVM Caeli lidar, Netherlands, 16RIVM Caeli lidar, Netherlands, 16thth April AprilCourtesy of Arnoud Apituley <[email protected]>Courtesy of Arnoud Apituley <[email protected]>

• This lidar is not operated all the time but has Raman capability• Further images here:

http://cerberus.rivm.nl/lidar/Cabauw/2010/

Volcanic ash just above boundary-layer

Cabauw EZ-lidar, Netherlands, 16Cabauw EZ-lidar, Netherlands, 16thth April AprilCourtesy of David Donovan, KNMI <[email protected]>Courtesy of David Donovan, KNMI <[email protected]>

Ash appears not to mix into the boundary layer as

it did over Chilbolton…

As over Chilbolton, ash much more depolarizing than ordinary

boundary-layer aerosol


Is this volcanic ash too? Why does it not mix into

the boundary layer?

De Bilt radiosonde put midday boundary-layer top at ~1 km


• Further images: http://www.knmi.nl/~knap/lidar_cabauw/

Another layer coming in?

ThursdayThursday1515thth, 1329, 1329

Summary from MODIS images

• Icelandic wind from northwest

• Further images: www.sat.dundee.ac.uk

Volcanic ash

FridayFriday1616thth, 1234, 1234

• Volcano obscured by clouds

Dilute volcanic ash measured over southern England and the Netherlands with lidar, signs of reaching the ground in England

SaturdaySaturday1717thth, 1317, 1317

• Wind at Iceland from the north

• Volcanic ash heading south behind a cold front

Cold front

Volca

nic a

sh

No depolarizing aerosol observed over Chilbolton or Cabauw

SundaySunday1818thth, 1222, 1222

• Northerly winds weakening

Is this the ash above the cloud?

Weakening

front

Not much sign in the MODIS image of the depolarizing aerosol observed at Cabauw but could be optically thin

observations of volcanic ash by lidar, modis and surface air-quality measurements robin hogan...

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