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Physik der Atmosphäre

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High Resolution Airborne DIAL Measurements of Water Vapor and Vertical Humidity Fluxes during IHOP

Christoph Kiemle, G. Ehret, A. Fix, H. Flentje, G. Poberaj, M. Wirth (DLR)R. M. Hardesty, W. A. Brewer, S. P. Sandberg (NOAA)

IHOP Water Vapor Intercomparison Workshop, Boulder, 2.10.2003

Overview

• Differential-Absorption-Lidar (DIAL) in the DLR Falcon aircraft• High resolution water vapour measurements of the boundary layer• Evaluation of systematic and statistical uncertainties• Co-located wind lidar measurements and vertical humidity fluxes

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IHOP Objectives and DIAL Performance

IHOP 2002missions

Objectives Falconflights

H2Odata

(hh:mm)

aerosoldata

(hh:mm)

H2O /aerosol

in %

BLheterogeneity

11 10:21 25:57 39,9

BL evolution

Improve understanding of the relationshipbetween atmospheric water vapor,surface fluxes and boundary layer

processes as they relate to quantitativeforecasts of precipitation

2 2:29 5:09 48,1

ConvectionInitiation

3 3:19 9:32 34,8

Low level jet

understand and predict the processesthat determine where and when

convection forms5 4:34 10:43 42,7

TOTAL 21 20:43 51:21 40,4

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H2O DIAL: Operators’ seat

with quick-look displayH2O DIAL: Telescope, detectorsand passive cooling unit

On board the DLR Falcon

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DIAL System Parameters and Set-up

Wavelength(nm)

927 1064 532

Pulseenergy (mJ)

12 50 40

Repetitionrate (Hz)

50(on/off)

100 100

Pulselength (ns)

7 15 11

Bandwidth(GHz)

0.14 / 90 0.05 0.05

Detector Si:APD Si:APD(s&p pol)

PMT(s&p pol)

FilterFWHM (nm)

1 1 1

Filter trans.(%)

65 40 55

Telescope Cassegrain, Ø35 cmfield-of-view: 1 - 2 mrad

Dataacquisition

14 bit, 10 MHz

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T,P,q

u,v,w,TAS

Dropsondes:u,v, P,T,q

HRDL:Horizontal & vertical wind speed

DIAL:H2O, AerosolsW'u,v

Falcon payload during IHOP_2002

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High Resolution Backscatter and Water Vapour Cross Section

H2O data: 73 m hor. res., 100 m vert. res. in near range, 300 m in far range; overall stat. error 7%

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Water Vapour Spectra and Variance Profile

0.0 0.2 0.4 0.6 0.8 1.0 1.2

km asl.

water vapor variance profile (g/kg)

uncorr. stat. err. variance (dashed)

2

3.0

2.5

2.0

energy spectra of horizontal water vapor series at 2450m asl.

0.0001

0.001

0.01

0.1

(g/kg)2

10000 1000wavelength [m ]

energy spectra of horizontal water vapor series at 1820m asl.

0.0001

0.001

0.01

0.1

(g/kg)2

10000 1000wavelength [m]

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Method for Estimating the Statistical (Random) Error

autocovariance of horizontal water vapor series at 1820m asl.

-0.2

0.0

0.2

0.4

0.6

(g/kg)2

-2000 -1000 0 1000 2000 3000 4000lag [m]

1.0

1.5

2.0

2.5

3.0

3.5

0 10 20 30

Mean of 450 profiles with zeff = 100 m, x = 146 m (Reference = High resolutions)

Mean of 450 profiles with zeff = 150 m, x = 146 m (Low vertical resolution)

Mean of 225 profiles with zeff

= 100 m, x = 292 m (Low horizontal resolution)

IHOP, 7 June 2002, 17:39 - 17:46:30 UTC

Rel. Stat. Uncert. of Water vapor Mixing Ratio (RMS), %H

eig

ht a

.s.l.

, km

2321 zxq

q

σ2q,instr.

σ2q, atmos.

qq

qerrorRMS noise

Assumption: hor. homogeneity DIAL resolution scaling law

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Discussion of Systematic Uncertainties

1.0

1.5

2.0

2.5

3.0

3.5

3 4 5 6 7 8

-3 hPa +3 hPa -2 K +2 K BSR1

Dropsonde

IHOP, 7 June 2002, 17:39 - 17:46:30 UTC

SP = 96 % SP = 95 % SP = 94 %

Water vapor Mixing Ratio, g/kg

Hei

ght

a.s

.l.,

km

Reference profile (SP=95%) with dropsonde and “worst case”

systematic deviations

1.0

1.5

2.0

2.5

3.0

3.5

-5 -4 -3 -2 -1 0 1 2 3 4 5

-3 hPa +3 hPa -2 K +2 K BSR1

IHOP, 7 June 2002, 17:39 - 17:46:30 UTC

SP = 96 % SP = 94 %

Difference to SP95, %

Hei

ght

a.s

.l.,

km

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Summary of DIAL Uncertainties for IHOP 2002

Error source Worst caseuncertainty

Maximum H2Orel. uncertainty

Comments Remedy

H2O absorptioncross-section

TBD TBD Line-dependent,significant

Accurate line parametermeasurement

Rayleigh Dopplereffect

TBD usingsimulation

model

< 1 %(Ismail & Browell,

1989)

Dependent on aerosoland water vapour

gradients

Use correction schemebased on temperature

and aerosol backscatter

Atm. pressure 3 hPa < 0.5 % Small

Atm. temperature 2 K 4 % Significant Use temp. indep. line

Spectral purity 1 % Nearrange

1 %

Farrange

4 %

Range-dependent,significant

Laser SP > 99 %, morestable conditions

Total systematic uncertaintywithout absorption cross-

section uncertainty

4.3 % 5.8 % Geometrically added:errors are assumed to

be “random”

Estimated statistical uncertainty forhorizontal and vertical resolutionsof ~1.5 km (10 s) and 200 m

0.5 % 3.4 % Dependent on range,background light,laser power, etc.

Overall uncertainty (preliminary) 4.8 % 9.2 % Algebraically added

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H2O DIAL Comparisons with Dropsondes

1

2

3

4

5

6 8 10 12 14

100.21W, 36.56N

June 9, 2002, 12:51 UT

H2O DIAL

Dropsonde

H2O Mixing Ratio [g/kg]

Alt

itu

de

[km

]

1

2

3

4

5

2 4 6 8 10 12 14

102.71W, 36.55N

June 9, 2002, 13:17 UT

H2O DIAL

Dropsonde

H2O Mixing Ratio [g/kg]

Alt

itu

de

[km

]

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High Resolution Water Vapor and Vertical Wind

-101.92 -101.90 -101.88 -101.86 -101.84 -101.82lo ng itud e

1.01.5

2.0

2.5

3.0

heig

ht (k

m)

1 .01.5

2.0

2.5

3.0

3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 g /kg

DLR DIAL wa te r va p o ur m ixing ra tio

0 2 4 6 8 10d ista nc e (km )

1.5

2.0

2.5

3.0

3.5

heig

ht (k

m)

1 .5

2.0

2.5

3.0

3.5

-3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 m /s

NO AA HRDL ve rtic a l wind ve lo c ity

DLR-DIAL:

x = 150 m

y = 150 m

NOAA-HRDL:

x = 150 m

y = 150 m

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Co-located Airborne Water Vapour and Wind Lidars

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Estimation of Latent Heat Flux Profile by Eddy Correlation

Flux F = w’q’ q’ = q - q

statistical error (solid):

σ2F, instr. = Δt/T σ2

w atm. σ2q, instr.

Ritter et al., JGR, 1990

sampling error (dashed):

σ2F, sampling =

2 ISF/T (F2 + σ2w atm. σ2

q, atm.)

Lenschow and Stankov, JAS, 1986

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