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
Martin Hagen > ISTP 2019 > Toulouse, France > 20 - 24 May 2019 3
Synergetic Measurements Poldirad – miraMACS
Martin Hagen > ISTP 2019 > Toulouse, France > 20 - 24 May 2019 4
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
Martin Hagen > ISTP 2019 > Toulouse, France > 20 - 24 May 2019 5
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
Martin Hagen > ISTP 2019 > Toulouse, France > 20 - 24 May 2019 6
-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
Example Measurement 2019-01-09 12:09
Martin Hagen > ISTP 2019 > Toulouse, France > 20 - 24 May 2019 7
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
Example Measurement 2017-02-08 09:08
Martin Hagen > ISTP 2019 > Toulouse, France > 20 - 24 May 2019 8
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
Martin Hagen > ISTP 2019 > Toulouse, France > 20 - 24 May 2019 9
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
Martin Hagen > ISTP 2019 > Toulouse, France > 20 - 24 May 2019 10
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
Martin Hagen > ISTP 2019 > Toulouse, France > 20 - 24 May 2019 11
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
Martin Hagen > ISTP 2019 > Toulouse, France > 20 - 24 May 2019 12
µm
IWC = 0.1 g/m3
Profile at 16 km (2019-01-09 12:09)
Retrieval of Microphysical Properties of Ice Particles
Martin Hagen > ISTP 2019 > Toulouse, France > 20 - 24 May 2019 13
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
Retrieval of Microphysical Properties of Ice Particles
Martin Hagen > ISTP 2019 > Toulouse, France > 20 - 24 May 2019 14
-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]
T-matrix simulations
for Gamma distributions
of spheroid ice particles
T-matrix simulations
for Gamma distribution
of cylindrical ice particles
0 1 2 3 4 5
median volume diameter [mm]
16
14
12
10
8
6
4
2
0
du
al-
wave
len
gth
ra
tio
[d
B]
0 1 2 3 4 5
median volume diameter [mm]
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
Retrieval of Microphysical Properties of Ice Particles
Martin Hagen > ISTP 2019 > Toulouse, France > 20 - 24 May 2019 15
-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]
T-matrix simulations
for Gamma distributions
of spheroid ice particles
T-matrix simulations
for Gamma distribution
of cylindrical ice particles
0 1 2 3 4 5
median volume diameter [mm]
16
14
12
10
8
6
4
2
0
du
al-
wave
len
gth
ra
tio
[d
B]
0 1 2 3 4 5
median volume diameter [mm]
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
Martin Hagen > ISTP 2019 > Toulouse, France > 20 - 24 May 2019 16