Investigation of Ice Microphysics using Simultaneous ... · Investigation of Ice Microphysics using...

Investigation of Ice Microphysics

using Simultaneous Measurements

at C- and Ka-Band

Martin Hagen1, Florian Ewald1, Silke Groß1, Qiang Li1

Bernhard Mayer2, Gregor Möller2, Eleni Tetoni1, Tobias Zinner2

1 Institut für Physik der Atmosphäre, DLR Oberpfaffenhofen, Germany 2 Meteorologisches Institut, Ludwig-Maximilians-Universität München, Germany

Key Questions:

when does precipitation initiation take place?

when will ice be formed?

how is precipitation initiation related to ice formation?

Understanding Precipitation Initiation in Mixed Phase Clouds

Martin Hagen > ISTP 2019 > Toulouse, France > 20 - 24 May 2019 2

aft

er

Hö

ller,

19

94

development of an single isolated convective cell

cloud, ice

rain, graupel

hail

downdraft

updraft

0°C

-15°C

Radar point of view:

dual-polarization hydrometeor classification

reflectivity gives water / ice content

ZDR, KDP, … tells about particle habit

Limitation:

weather radar (X-, C-, S-) is not sensitive enough for small cloud particles

cloud radar (Ka- or W-band) is affected by Mie resonance effects and

suffers from attenuation

both can derive only partly microphysical quantities or particle habits

Understanding Precipitation Initiation in Mixed Phase Clouds

aft

er

Hö

ller,

19

94

development of an single isolated convective cell

cloud, ice

rain, graupel

hail

downdraft

updraft

0°C

-15°C


Synergetic Measurements Poldirad – miraMACS


POLDIRAD (DLR) miraMACS (LMU)

OpenTopoMap (CC-BY-SA)

Coordinated RHI Measurements Poldirad – miraMACS

STAR: simultaneous transmit and receive

AltHV: alternate transmit and receive horizontal and vertical


C-band weather radar

(5.5 GHz, 250 kW)

operated at DLR Oberpfaffenhofen

4.5 m antenna 1° beam-width

range res. 150 m, max 120 km

full polarimetric (STAR and AltHV)

(ZDR, LDR, KDP, rhoHV)

MIRA35

scanning Ka-band cloud radar

(35.2 GHz, 30 kW)

operated at LMU Munich city

1 m antenna 0.6° beam-width

range res. 30 m, max 22 km

linear depolarization ratio LDR

POLDIRAD (DLR) miraMACS (LMU)

0 10 20 30 40

range [km]

Example Measurement 2019-01-09 12:09


-20 -10 0 10 20

23 km

LMU DLR

Z Ka

Z C

Z C – Z Ka

30

20

10

0

-10

-20

-30

-40

-50

-60

dual wavelength ratio [dB] 30

25

20

15

10

5

0

-5

-10 0 10 20 30 40

range [km]

reflectivity [dBz] 14

12

10

8

6

4

2

0

14

12

10

8

6

4

2

0

he

igh

t [k

m]

heig

ht [k

m]

14

12

10

8

6

4

2

0

heig

ht [k

m]

dual-polarization

observations

MIRA

LDR: linear

depolarization ratio:

irregular shapes

POLDIRAD

ZDR:

differential

reflectivity:

elongated

particles

depolarization signal

to weak to be seen



LDR Ka

ZDR C

0 10 20 30 40

range [km]

14

12

10

8

6

4

2

0 h

eig

ht [k

m]

14

12

10

8

6

4

2

0

heig

ht [k

m]

0 10 20 30 40

range [km]

-10.0

-12.5

-15.0

-17.5

-20.0

-22.5

-25.0

-27.5

-30.0

2.0

1.5

1.0

0.5

0.0

-0.5

-1.0



Z Ka

Z C

Z C – Z Ka

no

Ka

C

Ka

+C

Minimum detectable/discernible

signal (MDS):

C-band POLDIRAD:

(1 µs pulse, 64 samples)

~ -26 dB at 5 km

~ -17 dB at 15 km

Ka-band miraMACS:

(0.2 µs pulse, 256 samples)

~ -40 dB at 5 km

~ -31 dB at 15 km

Sensitivity Issue – MDS


50 scans 2017

Median volume diameter Dm

dual-wavelength ratio

DWR = 58 Dm1.66 (Matrosov, 1998)

Ice water content IWC

e.g. Protat et al., 2007:

log10(IWC) = aZT + bZ + cT + d

(T temperature, Z reflectivity Ka)

Particle shape and Particle size

distribution

look-up tables derived from

T-matrix simulations

Effective radius reff

known particle habits, DWR

Retrieval of Microphysical Properties of Ice Particles


IWC = 0.1 g/m3

reflectivity [

dB

z]

effective ice crystal radius [µm]

dual wavelength reflectivity ratio C/Ka [dB]

reflectivity C

-band [

dB

z]

Mass-size relationship

spheroid approximation

(Hogan et al., 2011)

cylinder approximation

aspect ratios 0.6, 1, 1.4

mass approximation

based on various world-wide field campaigns

(Brown and Francis, 1995)

M(D) = 1.677 e-1 D2.91 D <= 0.01 cm

M(D) = 1.66 e-3 D1.91 0.01 < D <= 0.03 cm

M(D) = 1.9241 e-3 D1.9 D > 0.03 cm

T-Matrix Simulations of Ice Particle


Particle size distribution

modified gamma function

fitted to same in-situ data

used for M(D) normalized

by the volume-weighted

diameter Dm and the

intercept parameter N0

(Delanoë et al., 2014)

Effective radius

𝑟𝑒𝑓𝑓 =𝑚 3

𝑚 2=volumearea

r >> λ

T-Matrix Simulations of Ice Particle


µm

IWC = 0.1 g/m3

Profile at 16 km (2019-01-09 12:09)



dual-wavelength

ratio

Z C

DWR

0 10 20

range [km]

14

12

10

8

6

4

2

0

heig

ht [k

m]

14

12

10

8

6

4

2

0

heig

ht [k

m]

0 10 20

range [km]

6

5

4

3

2

1

0

heig

ht [k

m]

6

5

4

3

2

1

0

6

5

4

3

2

1

0

6

5

4

3

2

1

0 -60 -40 -20 0 20 40 60

reflectivity [dBz]

-5 0 5 10 15 20

dual-wavelength ratio [dB]

Z Ka Z C

0.0 0.1 0.2 0.3 0.4 0.5

ice water content [g m-3]

0 2 4 6 8 10

median volume diameter [mm]

median volume

diameter

ice water

content reflectivity

T-matrix simulations for spheroid and cylinder ice particles

using different particle axis ratios: 0.6, 1, 1.4

using different size parameters of a gamma size distribution: 0 and 1



-5 0 5 10 15 20

dual-wavelength

ratio [dB]

0 2 4 6 8 10

median volume

diameter [mm]

dual-wavelength

ratio

median volume

diameter 6

5

4

3

2

1

0

6

5

4

3

2

1

0

heig

ht [k

m]


for Gamma distributions

of spheroid ice particles


for Gamma distribution

of cylindrical ice particles

0 1 2 3 4 5


16

14

12

10

8

6

4

2

0

du

al-

wave

len

gth

ra

tio

[d

B]

0 1 2 3 4 5


16

14

12

10

8

6

4

2

0

du

al-

wave

len

gth

ra

tio

[d

B]

T-matrix simulations for spheroid and cylinder ice particles

using different particle axis ratios: 0.6, 1, 1.4

using different size parameters of a gamma size distribution: 0 and 1



-5 0 5 10 15 20

dual-wavelength

ratio [dB]

0 2 4 6 8 10

median volume

diameter [mm]

dual-wavelength

ratio

median volume

diameter 6

5

4

3

2

1

0

6

5

4

3

2

1

0

heig

ht [k

m]


for Gamma distributions

of spheroid ice particles


for Gamma distribution

of cylindrical ice particles

0 1 2 3 4 5


16

14

12

10

8

6

4

2

0

du

al-

wave

len

gth

ra

tio

[d

B]

0 1 2 3 4 5


16

14

12

10

8

6

4

2

0

du

al-

wave

len

gth

ra

tio

[d

B]

spheroid

ice

prolate

ice

Dual-polarization C- and Ka-band Retrieval:

reflectivity ice water content IWC

dual-wavelength reflectivity ratio median volume diameter

effective radius of ice particles

particle habit through T-matrix

simulations

dual-polarization hydrometeor classification

particle habit

The IcePolCKa project is sponsored

within DFG SPP 2115 PROM

Multi-Wavelength Microphysics Retrieval


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