The Vertical Structure of Liquid Water Content in Shallow ......The Vertical Structure of Liquid...
Transcript of The Vertical Structure of Liquid Water Content in Shallow ......The Vertical Structure of Liquid...
The Vertical Structure of Liquid Water Content in Shallow Clouds as Retrieved from Dual-wavelength Radar Observations
Zeen Zhu1, Katia Lamer2, Pavlos Kollias1 , Eugene E. Clothiaux3
1Stony Brook University2 CUNY City College of New York3 Pennsylvania State University
June 12, 2019
Motivation
- Radar Z = 0.048 ∗ LWC+ [Atlas, 1954]
-Microwave Radiometer & Radar
LWC, =-./
0.1
∑/345 ./
0.1∆7[Frisch et al., 1998]
- Dual-wavelength technique
Limited to reflectivity accuracy and drizzle occurrence
No priori assumption of LWC distributionNot affected by radar calibrationNot affected by drizzle occurrence
[Hogan et al., 2005]
How to retrieve LWC in warm cloud?
MethodologyZ8 = Z9 − 2∫9
7 α8 + κ8LWC dh
Unattenuated
Observed
GasLiquid
Two wayW Ka
Known
DWR7 dB = ZEF h − ZG h = −2H9
7
[αJK−αLM + kJK − kLM LWC]dh
Cloud Top
Cloud Base
KaW
dBZ [Hogan et al., 2005]
MethodologyWell matched radar observation in beam width, range resolution and sampling time
Constrain random observational uncertainty
Ka/W-SACR2 operating on ENA site provide us a best opportunity to apply DWR technique
∆Z8 =4.343∆tPRF8M
(λPRF8
4πX+σZ,8
+1
SNR8++
2SNR8
)X+
∆LWC =(∆Z8X
+ + ∆Z8++ )
X+
2(k8X − k8+)∆h
[Hogan et al., 2005]
∆Z8 ~ 0.2 dB
∆LWC ~ 4 g mcJ ‼
∆t = 2s∆h = 12.5m
Need to reduce random error
Averaging profiles in time and considering a vertical window to account for more observation to reduce error
Jun 21- Oct 15, 2016
Uncertainty Estimation
Liquid
Wate
r Cont
ent
Uncer
tainty (
g m-3 )
0-5050-100
100-150150-200
200-250250-300
300-350350-400
400-450450-500
500-550550-600
600-650650-700
Cloud thickness (m)
LWP Re
trieve
d-LW
P MW
R
LWP M
WR
(%)
Number of 30-s profiles in each cloud thickness subgroup
���
���
���
���
Liqu
id W
ater C
onten
t Un
certa
inty (
g m-3
)
0-5050-100
100-150
150-200
200-250
250-300
300-350
350-400
400-450
450-500
500-550
550-600
600-650
650-700Cloud thickness (m)
LWP R
etrie
ved
-LW
P MW
R
LWP M
WR
(%)
Number of 30-s profiles in each cloud thickness subgroup
���
���
���
���
Modified Frisch approach work well for thin cloud DWR technique
[N. Küchler.,2018]
Thick cloud, more drizzle
Retrieval EvaluationObserving System Simulation Experiments (OSSEs)
���
Dual wavelength ratio [DWR]
Ka/W band radar reflectivity (dBZ) Liquid water content (g m-3)Dual wavelength ratio [DWR]
Ka/W band radar reflectivity (dBZ) Liquid water content (g m-3)
Dis
tanc
e fr
om c
loud
bas
e (m
)D
ista
nce
from
clo
ud b
ase
(m)
Input LWCRetrieved LWC
Input LWCRetrieved LWC
���
��� ���
��� ���
Liqu
id W
ater
Con
tent
U
ncer
tain
ty (g
m-3
)
0-5050-100
100-150
150-200
200-250
250-300
300-350
350-400
400-450
450-500
500-550
550-600
600-650
650-700Cloud thickness (m)
LWP R
etri
eved
-LW
P MW
R
LWP M
WR
(%)
Number of 30-s profiles in each cloud thickness subgroup
���
���
���
���
Comparison with MWR- retrieved LWP
The proposed technique can capture the shape for both linear and nonlinear LWC distribution
LWP comparison with MWR indicates no systematic bias of the retrieval
Impact of Dynamics on Vertical Distribution of LWC
Cloud top mean Doppler velocity (ms-1)Updraft(0-0.3) Downdraft(0.3-0.6) Median
Nor
mal
ized
hei
ght
300 -400m400 -500m
Cloud thickness
Downdraft velocity at cloud top
Lower LWC in the upper part of the cloud
Entrainment ?
300 -400m400 -500m
Impact of Rain Rate on Vertical Distribution of LWC
Cloud base rain rate (mm hr-1)0.001-0.03 0.1-0.5
Nor
mal
ized
hei
ght
Median
Cloud thickness
Increasing rain rate at cloud base
More liquid water in the lower part of the cloud
LWC Profile LinearityCan LWC profile be represented linearly within cloud ?
Cloud base
Cloud top
𝐋𝐖𝐂=𝚪𝐡+𝐛
Yes
*More details see Zeen Zhu, Katia Lamer, Pavlos Kollias, Eugene E. Clothiaux, 2019: The Vertical Structure of Liquid Water Content in Shallow Clouds as Retrieved from Dual-wavelength Radar Observations.
No!
On average, general LWCprofiles are well capturedby a linear profile
LWC distribution is poorlycaptured by linear for somespecific process
LWC Profile Adiabaticity
Liquid water content (gm-3)
Hei
ght a
bove
clo
ud b
ase
Cloud thickness(m) Degree of adiabaticity200-300 f = 0.66300-400 f = 0.55400-500 f = 0.4500-600 f= 0.22
Adiabatic LWCDegree of adiabaticity fad ?
Decrease
LWC z = fFoΓFoz [Wood., 2006]
The shape of the LWC profile in clouds is affected by cloud dynamics and precipitation rate. Can high-resolution models reproduce this behavior?
The degree of adiabaticity decreases with cloud thickness.Is this a response to stronger dynamics and turbulence?
Conclusion & Future work
We are currently working on joint vertical air motion and LWC retrievals in cumulus clouds
We plan to release the retrievals for ACE-ENA.
Zeen Zhu, Katia Lamer, Pavlos Kollias, Eugene E. Clothiaux, 2019: The Vertical Structure of Liquid Water Content in Shallow Clouds asRetrieved from Dual-wavelength Radar Observations . submitted.
LWC Profile LinearityD
epth
(m)
LWP(
gm-2
)
All
Cloud top velocity (m s -1) Cloud base velocity (m s -1) Rain rate (mm hr-1) at cloud base Updraft Downdraft Updraft Downdraft
0.0 to 0.3
0.3 to 0.6
0.0 to 0.3
0.3 to 0.6
0.0 to 0.3
0.3 to 0.6
0.0 to 0.3
0.3 to 0.6
0.001to 0.03
0.03 to 0.1
0.1 to 0.5
100-
200
m
93±4
5 0.380.270.97510
0.480.290.97121
-0.61 0.97 0.60
8
0.430.24,0.97292
0.290.320.9273
0.500.180.9562
0.050.43 -0.04
28
0.330.320.93156
0.400.270.93116
0.360.270.96296
0.500.220.96149
0.350.330.9372
200-
300
m
137 ±
57 0.33
0.310.97901
0.410.270.97203
0.31 0.34 0.66 520
0.330.310.96520
0.270.320.89131
0.370.290.97128
0.310.280.9267
0.320.320.89328
0.340.300.98198
0.380.280.95493
0.340.300.97253
0.190.370.80 147
300 -
400
m
196±
67 0.39
0.320.89608
0.470.300.90113
0.62 0.18 0.90 14
0.400.320.84321
0.130.370.6491
0.390.330.91120
0.370.260.9438
0.400.310.85216
0.360.340.82125
0.510.260.97187
0.460.290.89199
0.170.420.49212
400-
500
m
265±
102 0.35
0.330.94390
0.480.280.90113
0.56 0.30 0.51
7
0.310.340.92187
0.170.370.6647
0.380.300.9277
0.450.280.9433
0.320.340.89141
0.280.330.9365
0.460.250.8973
0.500.280.98131
0.180.390.76 176
500 -
600
m
347±
183 0.25
0.350.96219
0.320.340.8749
0.60 0.20 0.65
5
0.240.330.84106
0.210.400.5431
0.260.340.7239
0.410.330.6623
0.300.270.8557
0.150.400.6952
0.510.220.8926
0.480.230.9666
0.090.420.73111
Table 1. Parameters of the linear fits LWC = a H + b.Within each cell (i.e., shaded row) the slope parameter a,the intercept b, the R2 value (in bold) of the fit to themedian, the number of 30-s profiles used in the fit (initalics) are presented in order from top to bottom. Resultswith R2 less than 0.8 are crossed-out.