Measurements of microphysical properties of convective clouds in the tropics and the mid-latitudes

Measurements of microphysical properties of convective clouds

in the tropics and the mid-latitudes

• Introduction: recent projects in convective clouds- Megha-Tropiques (MT) - HYMEX- HAIC-HIWC

• Measurement objectives in convective clouds:Ice microphysical properties of tropical and mid-latitude convective clouds

- Measurements: PSD and radar reflectivity- Ice particle morphology from 2D images- Area-diameter and mass-diameter relations - Retrieved IWC: various approaches

® main question: quantifying the ice mass in clouds and precipitation

Outline

2 aircraft campaigns have been performed in order to improve the rain rate retrieval in tropical convection.

MCS (squall lines) for MT1 MS for MT2 IC for MT2

13/08/2010 27/11/2011 08/12/2011

-Over West African Continent (Niamey/NIGER 08/2010), MT1.- All systems observed were Mesoscale Convective Systems

(MCS).

-Over Central Indian Ocean (Gan/MALDIVES , 11-12/2011), MT2.- 2 types of systems : the first 2 weeks, systems with Mesoscale expansion

(MS). the last 2 weeks, systems formed by Isolated Convection (IC).

Megha-Tropiques

SOP1 aircraft campaign HyMeX-SOP1, the field campaign dedicated toheavy precipitation and flash-flooding in Northwestern Mediterranean

Heavy precipitation events: Balearic Islands (BA), Catalonia (CA) and Valencia (VA) regions in Spain, Cévennes-Vivarais (CV) and Corsica (CO) in France, Central Italy (CI), Liguria-Tuscany (LT) and North-Eastern Italy (NEI) in Italy.

HYMEX

10.8µm infrared brightness temperature from MSG at 0730 UTC 26 October 2012.

Aircraft campaign performed out of Darwin for Aircraft Safety regulatory purposes (FAA, EASA) and scientific objectives

Primary objective is to provide 99th percentile total water content statistics, as a function of distance scale, to industry and regulators

Two types of convection for sampling :Oceanic convection (primary focus)Continental convection (secondary focus)

HAIC (High Altitude Ice Crystals)

Courtesy of HIWC

F20 aircraft (SAFIRE): Possibilities, limitations• The flight crew consists of:

– 2 SAFIRE pilots– 1 SAFIRE flight engineer (jump

seat)

– 1 SAFIRE operator– 3 engineers/scientists to operate

scientific instrumentation and lead F20 mission

• F20 limitations:– 4 under wing pylons, limited

fuselage hardpoints and electrical cabling

– Available power for scientific instrumentation: 8.4 kVA

Measurement challenges in convective clouds

Major requirements/challenges for instruments on F20: 1. A series of imaging instruments is needed to cover the range of expected cloud

particle sizes from µm to mm ➔ Particle Size Distribution (PSD)

2. Deploy instruments for maximum bulk IWC measurements: ROBUST probe (actually combination probe with CDP), redesigned IKP

3. Instruments to measure very small cloud particle properties (<100μm, <50µm, if possible): CDP, CPSPD, CPI, …

4. Discriminate phase of cloud particles (populations): CPSPD, CPI, OAPs….

5. Avoid possible small ice crystals contamination on spectrometer data: Anti-shattering tips, inter-arrival time measurement & post processing.

6. Retrieve microphysics beyond flight trajectory: remote sensing.

Crystal growth after ice nucleation

Riming

Aggregation

Vapor diffusion

CPI (Cloud Particle Imager):data CNRS-LaMP

Crystal growth in convective clouds dominated by 3 major growth mechanisms:- diffusion ( fct (RHI, T): mostly small ice particles, sometimes up to 400 µm- riming (existing crystals collect supercooled droplets) - aggregation (important for high crystal concentrations)

have we understood these processes correctly?

are we able to describe themin an appropriate way for atmospheric models ?

French Falcon 20 (SAFIRE) in Niamey (NIGER)

Megha-Tropiques

CPI Cloud particle imager

RASTA (Cloud RADAR (94GHz)*

FSSP-ER (cloud droplet PSD)

PIP Precip. Imag. Probe

2DStereo 2D/3D imaging

Instruments used within MT

CIP Cloud. Imager. Probe

2010/2011

Bulk TWC and PSD from optical spectrometersIKP, ROBUST, 2mmLWC: TWC

CDP: PSD smallest particles

PSD from particle images

1 mm

2D-S: Intermediate size particles (PSD < 1mm)

6 mm

PIP: Largest particlesPSD > 1mm

Combined PSD covering entire size range of hydrometeors

Combined PSD covering entire size range of hydrometeors

A series of instruments needed to cover the entire range of expected cloud particle sizes: µm to mm range for PSD of hydrometeors!!

100

101

102

103

104

10-6

10-4

10-2

100

102

104

Deq(µm)

#/L/

µm

Merging different instruments to retrieve total PSD

PIP

CIP2DS

PSD composition

« Pristine » range fit(80 µm,250 µm)

« Drizzle » range fit(250 µm,1500 µm)

Precipitation range fit(1500 µm,5000 µm)

MT1

MT2

Measurements: Averaged PSD and radar reflectivity

T [°

C]T

[°C]

Dmax [µm]

Dmax [µm]

Comparing radar reflectivity from ground observations with in-situ microphysics

MT1 (Niger, 2010) , observed reflectivity range : 10 – 35 dBZ

Comparing radar reflectivity from ground observations with in-situ microphysics

by co-localization of aircraft and radar pulse volume

Analyzing the microphysics behind reflectivity from ground observations

3 number distributions of solid hydrometeors ( 1 min averages) ➝ different in number

IWC = 0.6 g m-3

IWC = 1.2 g m-3

IWC = 1.9 g m-3

➝ different in mass

but,in all 3 cases the surface radar gives the same reflectivity of 28-29 dBZ

however,Cloud Radar reflectivity(94GHz) well distinguishes the microphysicaldifferences of the 3 spectra

2D images => density & m(Dmax) ?

Ice particle morphology from 2D images

max.DAreaprojected

Þn(Dmax) (PSD)

Ice particle morphology from 2D images

Area

[cm

²]

Dmax [cm]

#/L/

µm

Dmax [µm]

Calculation of the Mass-Diameter Relationship :

• PSD and reflectivity at 95GHz (RASTA) measured.• β is calculated with s from A(D) relationship:

=> α is calculated while matching simulated and measured 94GHz reflectivity (Tmatrix calculations for oblate particle with a flattening of 0.8).

Here: Results for MT1

5.125.2

α

β

α vs β vs Temperature

Area-diameter and mass-diameter relations

maxm D

Calculation of the IWC (CWC)

Comparison of IWC retrievals:

- Matching measured with simulated reflectivities via T-matrix- Baker & Lawson* method

Retrieved IWC: various approaches

*Baker, Brad, and R. Paul Lawson. “Improvement in Determination of Ice Water Content from Two-Dimensional Particle Imagery. Part I: Image-to-Mass Relationships.” Journal of Applied Meteorology and Climatology 45, no. 9 (September 2006): 1282–1290.Lawson, R. Paul, and Brad A. Baker. “Improvement in Determination of Ice Water Content from Two-Dimensional Particle Imagery. Part II: Applications to Collected Data.” Journal of Applied Meteorology and Climatology 45, no. 9 (September 2006): 1291–1303.

Calculation of the IWC (CWC) from T-matrix compared with IKP reference bulk IWCRetrieved IWC: various approaches