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.