Towards simultaneous retrieval of water cloud and drizzle using ground-based radar, lidar, and microwave radiometer

Transcription

1 Towards simultaneous retrieval of water cloud and drizzle using ground-based radar, lidar, and microwave radiometer Stephanie Rusli David P. Donovan Herman Russchenberg

2 Introduction microphysical structure Focus: single-layered, low level liquid water cloud with drizzle physical processes radiative properties Aim: hydrological cycle, earth energy budget, climate Simultaneous retrieval of cloud and drizzle microphysical properties

3 Measurements Sensor synergy: Sensor Radar Lidar Microwave radiometer Product reflectivity factor (Z) attenuated backscatter (β) brightness temperature (TB) Data: ACCEPT campaign: Oct 7 - Nov 18, 2014 in Cabauw Instruments: MIRA doppler radar: 35.5 GHz KNMI UV-lidar: 355 nm HATPRO microwave radiometer: 14 frequency channels between GHz and GHz

4 Model assumptions Droplet size distribution: n(r) = N Rn Γ(ν) r Rn ν -1 e (-r / Rn), r 0 unimodal gamma distribution (bimodal for drizzling cloud) moments are proportional to each other Vertical profile of liquid water content LWC: Boers et al LWC = LWCad x f(z) ; f(z) is controlled by Fr (sub-adiabatic fraction) W (vertical weight of liquid water distribution) W = 0.1 Fr = 0.9 W = 1.0 Fr = 0.6 Fr = 0.3 adiabatic

5 Forward models Sensor Forward model References Radar Rayleigh approximation: Z = 2 6 r 6 n(r) dr - 0 Lidar Microwave radiometer multiple scattering model considers absorption of O2, water vapour and liquid water Hogan 2006, Hogan 2008 Löhnert et al Retrieval technique: optimal estimation Allows a priori information

6 Retrieval - cloud part Retrieved parameters (state vector): [ x1, x2, x3, x4, x5, x6, x7 ] DSD shape parameter (independent of height) Vertical profile of LWC (Boers et al. 2006) Number concentration (constant) Cloud base and top Lidar calibration correction (constant)

7 Retrieval - cloud part Retrieved parameters (state vector): [ x1, x2, x3, x4, x5, x6, x7 ] DSD shape parameter (independent of height) Vertical profile of LWC (Boers et al. 2006) Number concentration (constant) Cloud base and top Lidar calibration correction (constant) Droplet size distribution: n(r) = N Rn Γ(ν) r Rn ν -1 e (-r / Rn), r 0

8 Retrieval - cloud part Retrieved parameters (state vector): [ x1, x2, x3, x4, x5, x6, x7 ] DSD shape parameter (independent of height) Vertical profile of LWC (Boers et al. 2006) Number concentration (constant) Cloud base and top Lidar calibration correction (constant) fixed Fr, varying W fixed W, varying Fr

9 Retrieval - cloud part Retrieved parameters (state vector): [ x1, x2, x3, x4, x5, x6, x7 ] DSD shape parameter (independent of height) Vertical profile of LWC (Boers et al. 2006) Number concentration (constant) Cloud base and top Lidar calibration correction (constant)

10 Retrieval - cloud part Retrieved parameters (state vector): [ x1, x2, x3, x4, x5, x6, x7 ] DSD shape parameter (independent of height) Vertical profile of LWC (Boers et al. 2006) Number concentration (constant) Cloud base and top Lidar calibration correction (constant)

11 Retrieval - cloud part Retrieved parameters (state vector): [ x1, x2, x3, x4, x5, x6, x7 ] DSD shape parameter (independent of height) Vertical profile of LWC (Boers et al. 2006) Number concentration (constant) Cloud base and top Lidar calibration correction (constant)

12 Retrieval - cloud part Retrieved parameters (state vector): [ x1, x2, x3, x4, x5, x6, x7 ] DSD shape parameter (independent of height) Vertical profile of LWC (Boers et al. 2006) Number concentration (constant) Cloud base and top Lidar calibration correction (constant) Microphysical properties: - liquid water content (LWC) - effective radius (Re) - extinction coefficient (α) - number concentration (N)

13 Retrieval - drizzle part Drizzle: Drizzle reflectivity: Zdata - Zcloud (when Zdata > Zcloud) 13 μm Redrizzle < 150 μm (Rosenfeld 2012) Redrizzle within cloud does not increase with height Drizzle in cloud Drizzle below cloud Radar Lidar Radar Lidar

14 Retrieval - drizzle part Drizzle in cloud Drizzle below cloud Radar Lidar Radar Lidar Parametrize LWCdrizzle: Vertical profile of drizzle LWC (Boers et al. 2006) Scaling factor for drizzle LWC Parametrize Redrizzle : power-law below cloud base exponential within cloud (Lu et al. 2012) using extinction coefficient below, at and above cloud base

15 Retrieval - cloud & drizzle Retrieved parameters (state vector): [ x1, x2, x3, x4, x5, x6, x7, x8, x9, x10, x11 ] cloud drizzle DSD shape parameter (independent of height) Vertical profile of LWC (Boers et al. 2006) Number concentration (constant) Cloud base and top Lidar calibration correction (constant) Cloud microphysics: - liquid water content (LWC) - effective radius (Re) - extinction coefficient (α) - number concentration (N) Drizzle DSD shape parameter Drizzle LWC or Re profile + Drizzle reflectivity: Zdata - Zcloud (when Zdata > Zcloud) Drizzle microphysics: - LWCdrizzle - Redrizzle - αdrizzle - Ndrizzle

16 Retrieval - cloud & drizzle Retrieval scheme: state vector cloud microphysics Zcloud ßmodel TB,data Zdata-Zcloud Zexcess Zmodel Zdata cost function + penalty smoothing TB,model ßdata Zdrizzle drizzle microphysics minimization Microphysics Model Data Penalty function: to enforce the restrictions on drizzle droplet size

17 ACCEPT data on Oct 26, 2014 Retrieval - ACCEPT lidar radar Retrieved Zdrizzle Retrieved Zcloud

18 Comparison with other retrievals (1) Cloud properties at 100 m above cloud base This retrieval Donovan et al. (2015)

19 Comparison with other retrievals (2) Using skewness of radar doppler spectra to detect precipitation onset (Kollias et al. 2011) Applying the technique (Luke & Kollias 2013) to ACCEPT data; radar reflectivity (0th moment) skewness (3rd moment) s > 0.1 skewness > 0.1

20 Comparison with other retrievals (2) Using skewness of radar doppler spectra to detect precipitation onset (Kollias et al. 2011) Applying the technique (Luke & Kollias 2013) to ACCEPT data; updraft downdraft cloud drizzle cloud s > 0.1 drizzle

21 Spectral decomposition Comparison with other retrievals (2) drizzle cloud Our retrieval drizzle cloud drizzle cloud

22 Comparison with other retrievals (3) Drizzle below cloud base Drizzle properties are retrieved using doppler radar and lidar (O Connor et al. 2005) Cloudnet product LWPdrizzle below cloud base This retrieval O Connor et al. (2005)

23 Summary - A method to simultaneously retrieve cloud and drizzle LWC vertical profile: Boers et al. (2006) Two drizzle cases: without and with detection below cloud base Drizzle is derived from the reflectivity excess Redrizzle `13 μm - Applied to data obtained during ACCEPT campaign - Results are mostly consistent with other retrieval techniques