Peters Gerhard, Fisher Bernd and Andersson Tage.

Boreal Environment Research: 7, 353-362,

(2002)

Rain Observations with a vertically looking Micro

Rain Radar (MRR)

BALTEX- GEWEX & PEP• Baltic Sea Experiment : Hydrological Cycle• Global Energy and Water Cycle Experiment• Precipitation and Evaporation Project

• Radar Rainfall– RR and Z depends on DSD– Height of Measuring Volume

• Extrapolation of radar measuring volume to surface includes significant uncertainties

MRR• FM-CW Doppler radar (24.1 GHz)• Power transmit 50mWatt• 30 heights• Minimum RR is 0.01mm

• DSD and Wwhere is the single particle backscattering cross section,

and is the spectral reflectivity as a function of the drop diameter D.

Z is referred to as the Equivalent Radar Reflectivity factor with units of mm6 mm-3

( )( )

( )

DN D

D

6

0

( )6

Z N D D dD

3

0

( ) ( )6

R N D D v D dD

3

0

( )6w

LWC N D D dD

0

0

2

f fdf

W

f df

( )D

( )D

Set Up

• Rainfall measurements– 1min– 50 m– German Baltic coast Zingst Peninsula

• Comparison with tipping bucket Rain Gauge– 30 minute– 5 months (summer)

MRR vs Weather Radar

• What is the Biggest source of Error with MRR measurements ?

• When Mie theory is Applied?

• When the Rayleigh Approximation is Applied?

• What’s About the Weather radar wavelength (λ = 5 cm to 10 cm)σ = 2700 to 3000 MHz (S-band)

• MRR (σ = 24.1 GHz or 1,24 cm) DSD and RR versus Z

Mie scattering occurs when the particles in the atmosphere are the same size as the wavelengths being scattered

Vertical Updrift Winds

Drops Diameter smaller in comparison to the wavelength of light

Peters et. al (2002)• What is main Assumptions Peters et al.

did raise for this study:

Liquid Precipitation

• What is the Rainfall Rate classification scheme they used

0.25 mm hr-1

Height Resolution was set to: 50m

Which Gate was Selected: 10th

Peters et. al (2002)• Rain Gauge: Rainfall F

and Resolution ΔF

• Rain Rate Resolution ΔR = ΔF / Δt

• Define the contribution of certain R to the total rainfall.

Frequency of High RR has increased Duration of most events < 30 min

Averaging process: underestimation of the actual occurring RR

1 minute resolution is not enough to reveal the true distribution of rain rate

They concluded that:

Which Rain Rates Contributed most? 0 – 0.25 mmhr-1

Peters et al. (2002) ΔR / R = 0.05• Differential water column (mm/mm hr-1)

Maximum Contribution From rain rate around0.2 mm hr-1

Highest rainfall Contribution From rain rate around ≤ 0.3 mm hr-1

The resolution of the gauge is not sufficient to represent rain rate classes

Peters et al. (2002)

Spectral Peak of velocity is about 6 m s-1 at lower gates

Above 1100m peak shift to 2 m s-1

Meting level appears as:1- Enhanced Reflectivity2- Step in Fall Velocity3- Apparent increase of RR

Peters et al. (2002)Comparison with Weather Radar: DWD9 hours of sampling51.48 km900m lowest WR measuring volumeAveraged of two subsequent samples of WR volumes

MRR data averaged between 500 and 1400 mMRR vertical resolution 100 m

Peters et al. (2002)Reflectivities below -5dBZ are missing, in weather radar (WR) data probably because they fall below the detectable threshold

Agreement between MRR Reflectivity and WR suggests that MRR measurements could be used for continuously updating the Z-R relationship

WR measurements could be linked to the rainfall at the surface by the use of MRR profiles

bZ a R

Saurabh Das, Ashish K. Shuklaand and Animesh Maitra.

Advances in Space Research 45 (2010) 1325-1243

Investigation of vertical profile of

rain microstructure at Ahmedabad in

Indian tropical region

Das et al. (2010)

• Rain Attenuation• Rain Classification• Vertical Profiles of rain

microstructure– DSD– Rain Rate– Liquid water content– Average Fall speed of drops

• Compare MRR DSD to Disdrometer

Set Up

1- MRR30 seconds200m (up to 6km)

2- Disdrometer30 seconds

Assumptions and Corrections for MRR: 1- W for lower air velocities2- Errors due to non-spherical drops ~ 6% at 10mm/hr are neglected

Das et al. (2010)

• Disdrometer– Transform vertical momentum of drops to an electrical signal (where:

amplitude is f(DD))– Terminal Velocity Drop diameter (Gunn & Kinzer 1949)

– Drop Size in 20 bins Range 0 – 5.5 mm– DSD Rain Rate

Assumptions1- Momentum is due entirely to fall velocity2- Drops are spherical3 - Acoustic Noise Errors are neglected4- Dead Time correction not applied

Rain Classification Scheme Based on:Vertical Reflectivity profile

1- Stratiform2- Mixed3- Convective

Das et al. (2010)Radar reflectivity profile for: (a) 16:21:30–20:43:30 UTC of 15/08/2006; (b) 02:42:30–11:47:30 UTC of 01/08/2006;(c) 20:39:30-23:55:00 UTC of 03/07/2006.

16:21:30–20:43:30 UTC of 15/08/2006Max R is 10.02 mm/hrBB at 4.6 - 5.2 km

16:42:30 UTC no bright band is visible Convective17:10:30 UTC bright bands with two peaks Mixed17:33:30 UTC a clear bb structure is visible Stratiform

Das et al. (2010)

17:33:30 UTC Stratiform

16:42:30 UTC Convective

17:10:30 UTC Mixed

Das et al. (2010)

15/08/2006 16:40:00 to 16:44:30

Convective

3a Z 3b Rain Rate3c LWC3d W3e Mean Drop Diameter3f DSD

Das et al. (2010)

15/08/2006 17:08:30 to 17:13:30

Mixed

3a Z 3b Rain Rate3c LWC3d W3e Mean Drop Diameter3f DSD

Das et al. (2010)

15/08/2006 17:28:30 to 17:33:30Stratiform3a Z 3b Rain Rate3c LWC3d W3e Mean Drop Diameter3f DSD

Das et al. (2010)MRR vs Disdrometer1- good agreement between MRR and

Disdrometer rainfall (r = 0.8)2- Scattering is higher above 2.5 mm/hr3- Stratiform Rain Bigger Drop Sizes near

ground level (7c)4- Convective Drops 0.5 mm are dominant5- Stratiform Drops are also around 1mm6- Mixed showed a mixture of drops sizes (7b)

MRR show very high concentration of smaller drops (7a)MRR measures drops in range 0.245 – 5.03 mmDisdrometer measures drops in range 0.3-5.5 mm

MRR is more sensitive to smaller Drops