Cloud Microphysical Properties Measured from Commercial Aircraft

 

Karl Beswick and Martin GallagherUniversity of Manchester, United Kingdom

Darrel BaumgardnerCentro de Ciencias de la Atmósfera, UNAM, México

Roy NewtonDroplet Measurement Technologies, USA

3rd International Conference on Transport, Atmosphere and Climate25-28 June 2012

Prien am Chiemsee, Germany

Acknowledgements

• IAGOS• Mike Poellet and David Delene

University of North Dakota• Bill Dawson

Droplet Measurement Technologies• Sarah Lance

NOAA/CIRES• UK Facility for Ground based Measurements

A facility of the UK National Centre for Atmospheric Science• This work has been supported in the UK by the

NERC and FAAM.

Presentation Guide

• Background

• Instrument Description

• Laboratory Studies

• Preliminary Results

• Next Generation BCP

Background

• IAGOSis a program for long-term observations of atmospheric composition on a global scale from a fleet of long-range aircraft.

• Allows the collection of observations on a scale impossible to achieve using research aircraft.

• Large scale measurements of cloud microphysical properties will help climate modelers improve and validate their models and provide extensive data to improve retrieval algorithms for satellite measurements.

• Particles pass through open laser beam

• Scattered light in the 144-156° cone is collected by photo-detector

• Signal is amplified, digitised and sized into size bins, size range 5-75µm diameter.

• No sample volume qualification: mathematical inversion is required.

BCP (Backscatter Cloud Probe)

12.5 cm

Flight Testing FAAM BAe 146

CDP 2-50 µmBCP 5-75 µmCAS 0.6-50 µmBCPD 1-50 µm

Example Data Sets NOTE: “Liquid Water” traces are NOT fully corrected

and NOT relevant to cirrus ice clouds – only used as indicator of relative volume changes.

No T-Matrix corrections applied to size distributions for suspected ice conditions.

Particle Size Distribution data is currently produced using Version 2 of the backscatter retrieval algorithm.

sizing camera

diagnostic camera

Evaporation tube, containing droplet generator

precision X-Y adjustable platform

water and air supplies

Beam mapping with droplet stream was conducted at the NOAA/Boulder Laboratory (courtesy of Sara Lance)

Computer controlled 3D micro-positioning stages (0.5 µm

accuracy)

Piezo electric droplet generator

High speed CCD imaging camera and microscope objective

Glare CCD

camera

Air drier

Liquid pump and solution reservoir

Auto-scanning micro-positioner to direct mono-disperse dropletsReproducible size AND Concentration. IAGOS Facility – Manchester (with thanks to Sara Lance)

Positioner rodSheath air

intake

Sheath flow

straighter

Evaporation flow tubeFlow tube nozzle

Interchangeable

Glare CCD

camera

Two Sizing Methods

fringe separation glare technique

15 µm dropsConstant inter-arrival time

Δt

Wave-form generator

Low Resolution Map of Cloud Spectrometer Sample Volume (no pin-hole mask used) Spatial resolution – 50 µm data

Medium Resolution Map – 10 µm spatial data completed

Data being processed

System has been automated based on initial input of of sample area location. Time for auto-scanning of sample area varies depending on instrument used (CDP, BCP

or CAS) and scan resolution used.50 µm displacement takes 1-2 hours. 10 µm takes 10-12 hours.

Inversion uses modified Twomy algorithm (Markowski, 1987, AST)

• Laser isn’t eyesafe• Operated with weight-on-wheels interlock switch

IAGOS-ERI Annual Meeting 2012, Lake Constance, June 18-20, 2012

Current well characterized Cloud Droplet Spectrometers

Test Flights on the North Dakota CitationSeptember-November. 2011

DMT LWC and CDP

Total number concentrations from BCP show reasonable agreement with CDP even with the sample volume close to the aircraft skin.

Yaw angle change?

The averaged size distribution, derived by inversion of the measured spectrum, agrees quite well with the CDP

The IAGOS instrument package was installed on board Lufthansa’s A340-300 'Viersen’. The maiden test flight was

launched from Frankfurt in July 2011

Summary of cloud concentrations : September, 2011 to May, 2012

Particle Characteristics

Take Offs and Landngs

Mid-Flight

Total Cloud Events

66% 54%

Cloud: Low Concentration

(<100 L-1)11% 28%

Cloud: High Concentration

(>100 L-1)50% 26%

Dust 14% 1%

Cloud/Dust Particle Encounters: 319 FlightsAverage Flight Duration > 8 Hours

Analysis of Luana, Angola to Frankfurt Flight, May 18, 2012

Maximum concentration > 300,000 per liter over Nigeria

Maximum ice water content > 2 grams per cubic meter(assumes spherical ice crystals (unrealistic)

Recent cloud particle measurements on May 18, 2012, Luanda, Angola to Frankfurt, Germany. More than 100,000 particles per liter at estimated temperature of -500 C !

Note: Temperatures not corrected for dynamic heating.

Large fluctuations of temperature in cloud!

30 Kt airspeed change

Aircraft takes avoidance action but remains in cloud for nearly half an hour and temperature measurements from IAGOS package remain corrupted by melted ice crystals.

High ice crystal concentrations corrupt temperature measurements by melting and wetting the sensor.

Average diameters are dominated by small crystalsMedian volume diameters are biased by very largest crystals

Average size distribution during cloud encounter: Bimodal with maximum number at 10 m but maximum LWC at 70 m

Vertical Profiles During Take Off and LandingShow Cloud Structure (Landing in Frankfurt Shown Here)

MultipleCloudLayers

Next Generation Instrument

The Backscatter Cloud Probe with Depolarization

(BCPD)

Measurements with the Cloud Aerosol Spectrometer with Depolarization (CAS-DPOL) distinguish droplets from crystals (courtesy James Dorsey, U. Manchester)

Polarization Detector to Sizing Detector

Pola

riza

tion R

ati

o

The BCPD, under development for IAGOS, will measure the perpendicular and parallel components of the polarized scattered light and identfy water droplets, ice crystals and ash/dust.

BCP-DPOL

Photo M. Gallagher, Manchester

BCD-D First test Flight March 2012. Photo M. Gallagher, Manchester

Cloud Tunnel results are encouraging.

A) The MVD as a function of time for the BCP-PD (red curve) and CDP (black),

B) LWC, C) Number

concentration and polarization ratio (blue curve) and D) average size distribution over the whole time period.

Ice phase

Water phase

Ottawa Cloud Tunnel Data: Courtesy DMT

Summary

• The BCP is currently taking detailed size-resolved cloud measurements that will enhance the current data base and lead to a better understanding of how clouds form, evolve and impact climate, e.g. microphysical properties of Contrails and Contrail induced cirrus Cirrus and Sub-visible cirrus

• The BCP cloud data base will be available for comparisons with satellite-derived cloud products.

• BCPs can warn flight crews of very high ice crystal concentrations.

• The next generation BCP, BCP-D may distinguish water droplets, ice, volcanic ash and dust.

For more information on the BCP/BCPD:

darrel.baumgardner@gmail.comwww.dropletmeasurement.com

Thank you for your interest.

BCP-100 V1 Brief Summary1.Software for assimilation and analysis of BCP database complete. Currently accepts, aircraft GPS position, altitude and temperature for interpretation. Software able to access multiple BCP data bases.2.Database for BCP complete – includes UK BAe 146, Viersen, Falcon, and two US aircraft studies. 3.Data seems consistent. Lower threshold may be higher than expected 6 µm as opposed to 5 µm under operational conditions.4.Intercomparison with BAe 146 CAPS-CAS, CDP-100 V2 complete. Data analysed and will be included in joint technical paper with DMT on BCP (in preparation, Baumgardner, Beswick et al.) together with data from US aircraft flights.5.New pylon canister mount being purchased to allow for parallel mounting of BCP and CDP on BAe 46 for better intercomparison checks (NERC FAAM-Manchester MSc Student)6.Routine detection over prevalent cloud regions e.g. Atlantic ITCZ. Profile data suggest consistent results.7.BCP appears able to detect dust particles based on consistent Middle East profile data under cloudless skies.8.Awaiting return of Viersen BCP to check

1. Calibration drift – this will be checked/validated using the new automated droplet gun calibration facility for sizing and absolute concentration. Two independent sizing methods – glare and interference fringe methods.

2. Diagnostics and laser inhomogeneity3. Power supply check etc.

9.NERC Grant awarded to develop BCP 2nd Generation instrument with polarisation capability. Delivery expected end 2012.