Peters Gerhard, Fisher Bernd and Andersson Tage. Boreal Environment Research: 7, , (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 W where 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

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: 10 th

Peters et. al (2002) Rain Gauge: Rainfall F and Resolution Δ F Rain Rate Resolution Δ R = Δ F / Δ t 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) Δ R / R = 0.05 Differential water column (mm/mm hr -1 ) Maximum Contribution From rain rate around 0.2 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 Reflectivity 2- Step in Fall Velocity 3- Apparent increase of RR

Peters et al. (2002) Comparison with Weather Radar: DWD 9 hours of sampling km 900m lowest WR measuring volume Averaged of two subsequent samples of WR volumes MRR data averaged between 500 and 1400 m MRR 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

Saurabh Das, Ashish K. Shuklaand and Animesh Maitra. Advances in Space Research 45 (2010) 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- MRR 30 seconds 200m (up to 6km) 2- Disdrometer 30 seconds Assumptions and Corrections for MRR: 1- W for lower air velocities 2- 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 Assumptions 1- Momentum is due entirely to fall velocity 2- Drops are spherical 3 - Acoustic Noise Errors are neglected 4- Dead Time correction not applied Rain Classification Scheme Based on: Vertical Reflectivity profile 1- Stratiform 2- Mixed 3- 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/ :21:30–20:43:30 UTC of 15/08/2006 Max R is mm/hr BB at km 16:42:30 UTC no bright band is visible Convective 17:10:30 UTC bright bands with two peaks Mixed 17:33:30 UTC a clear bb structure is visibleStratiform

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/ :40:00 to 16:44:30 Convective 3a Z 3b Rain Rate 3c LWC 3d W 3e Mean Drop Diameter 3f DSD

Das et al. (2010) 15/08/ :08:30 to 17:13:30 Mixed 3a Z 3b Rain Rate 3c LWC 3d W 3e Mean Drop Diameter 3f DSD

Das et al. (2010) 15/08/ :28:30 to 17:33:30 Stratiform 3a Z 3b Rain Rate 3c LWC 3d W 3e Mean Drop Diameter 3f DSD

Das et al. (2010) MRR vs Disdrometer 1- good agreement between MRR and Disdrometer rainfall (r = 0.8) 2- Scattering is higher above 2.5 mm/hr 3- Stratiform Rain Bigger Drop Sizes near ground level (7c) 4- Convective Drops 0.5 mm are dominant 5- Stratiform Drops are also around 1mm 6- Mixed showed a mixture of drops sizes (7b) MRR show very high concentration of smaller drops (7a) MRR measures drops in range – 5.03 mm Disdrometer measures drops in range mm MRR is more sensitive to smaller Drops