1 Implementation of the Ferrier cloud microphysics scheme in the NCEP GFS Masayuki Nakagawa, Hua-Lu Pan, Ruiyu Sun, Shrinivas Moorthi and Brad Ferrier NOAA/NWS/NCEP March 15, 2011

2 FEATURE Zhao & Carr (1997) [Modified version in GFS] Ferrier et al. (2002) [In Eta, WRF option] Prognostic variables Water vapor, cloud condensate (water or ice) Water vapor, total condensate (cloud water, rain, cloud ice, snow/graupel/sleet) Condensation algorithm Sundqvist et al. (1989) Asai (1965) [used in high res models] Precip fluxes and storage Top-down integration of precip, no storage, & instantaneous fallout. Precip partitioned between storage in grid box & fall out through bottom of box Precip type Rain, freezing rain, snow Rain, freezing rain, snow/graupel/sleet (variable rime density for precip ice) Mixed-phase conditions No coexistence of supercooled cloud water & ice, simple melting eqn. Mixed-phase at >-10C, includes riming, more sophisticated melting/freezing Comparing grid-scale microphysics schemes from Ferrier (2005)

3 Flowchart of Ferrier Microphysics RACW Cloud Water GROUND REVP Rain Water Vapor RAUT Sfc Rain CND ICND DEP Sfc Snow/Graupel/Sleet Cloud Ice Precip Ice (Snow/ Graupel/ Sleet) IACWR IEVP IACW IACR IMLT New process T < 0 o C T > 0 o C T>0, T<0 o C from Ferrier (2005) CNDCondensation (>0), evaporation (<0) of cloud water DEPDeposition (>0), sublimation (<0) of ice REVPRain evaporation RAUTAutoconversion of cloud to rain RACWAccretion of cloud water by rain IMLTMelting of ice IACWAccretion of cloud water onto ice IACWRAccretion of cloud water onto ice, liquid water shed to form rain IACRFreezing of rain to form ice, represented by multiple processes in code ICNDCloud water condensation onto melting ice, shed to form rain IEVPEvaporation from wet melting ice

4  Water vapor (q v ), total condensate (q t ) advected in model  Cloud water (q w ), rain (q r ), cloud ice (q i ), precip ice (“snow”, q s ) calculated in microphysics  Local, saved arrays store fraction of condensate in form of ice (F i ), fraction of liquid in form of rain (F r ) and fraction of ice in form of precip ice (F s ). Assumed fixed with time in column between microphysics calls. Note that 0  F i, F r, F s  1.  q t = q w + q r + q i + q s, q ice = q i + q s  F i = q ice /q t, F r = q r /(q w + q r ), F s = q s /q ice Deriving hydrometeors from total condensate

5 Original Ferrier and box Ferrier scheme  Original Ferrier (Moorthi) Cloud formation prior to saturation of a grid is not considered. Adjust grid-averaged relative humidity to a target RH, where the grid is effectively saturated. –98% for Δx = 12km, 90% for Δx = 100km  Box Ferrier Consider fractional cloud coverage in a grid box. Each grid box is divided into three parts. Ferrier microphysics scheme is applied separately to the cloudy and clear with precipitation portion of the grid.

6 It is necessary to introduce consideration of fractional cloud coverage in a grid box for use in GFS, since the Ferrier microphysics scheme is designed for use in high-resolution mesoscale model and do not consider partial cloud explicitly. Each grid box is divided into three parts. Ferrier microphysics scheme is applied separately to the cloudy and clear with precipitation portion of the grid. Cloud cover is obtained by the formulation of Sundqvist et al. (1989). Maximum-random cloud overlap is assumed. Consideration of partial cloud Ferrier microphysics Ferrier microphysics (evaporation, melting) CloudyClear with precipitation Clear w/o precipitation

7 Cloud cover is obtained by the formulation of Sundqvist et al. (1989). Water vapor in the clear portion of grid is assumed to distribute according to uniform PDF. To represent grid-scale condensation, increased water vapor is used to increase water vapor in the grid uniformly. Super-saturated water vapor is converted to cloud water through the Ferrier microphysics calculation. Cloud parameterization (1) x q*q* t-1 Schematic distribution of water vapor in grid. qvqv q*q* t-1 PDF of water vapor in grid. 1/(2  ) cloud cover super-saturated water vapor t t

8 Similarly, the grid is dried uniformly when other processes dry the grid. Cloud water evaporates through the Ferrier microphysics calculation to compensate sub- saturation of cloud part. Cloud parameterization (2) x q*q* t-1 Schematic distribution of water vapor in grid. qvqv q*q* t-1 PDF of water vapor in grid. 1/(2  ) t cloud cover sub-saturated water vapor t

9 Estimation of cloud cover and condensation Division of grid into three parts (cloud, clear with precipitation, clear without precipitation) Calculation of water properties in each parts (q v, q w, q i,…) Ferrier microphysics (cloudy, clear w/ precip. portion) Grid averaging Flowchart of box Ferrier scheme

10 Cloud condensate forecast 48 hour forecast of zonal mean cloud water + cloud ice. Initial time of forecast is 00 UTC 12 June Box Ferrier Zhao Cloud water/ice decreased in the upper troposphere and increased in the lower troposphere and the tropical mid troposphere.

11 Precipitation forecast 36 hour forecast of 24 hour accumulated precipitation. Initial time of forecast is 00 UTC 05 February Box Ferrier Zhao

12 Based on current operational GFS Box Ferrier scheme T382L64 resolution Started from June 2, 2008 Control: current operational GFS, T382L64 Experiment design (1st TEST)

13 dropout CNTL TEST Z500 anomaly correlation

14 Vector wind RMSE (Tropics) Vector wind RMSE Tropics TEST−CNTL Implementation of the box Ferrier scheme improved vector wind forecast over the Tropics.

15 Fit to RAOB (TEST, temperature) Cold bias in the upper troposphere and warm bias in the lower troposphere over the north America are prominent. Anl Ges 24-hr fcst 48-hr fcst

16 Sensitivity test 48 hour forecast of cloud water + cloud ice (left) and temperature (right) averaged over 30S-30N by Box Ferrier GFS. Differences from those using Zhao scheme. Initial time of forecast is 00 UTC 12 July =TEST Insufficiency of cloud ice is the cause of the cold bias in the upper troposphere. Cloud ice amount is sensitive to value of a parameter FLARGE, affecting fraction and number concentration of precipitating snow in Ferrier scheme.

17 T and cloud cover over NA Forecasts of temperature (top) and cloud cover (bottom) averaged over north America by GFS. TEST-CNTL. Initial time of forecast is 00 UTC 12 July Vertical axis is pressure (top) and model level (bottom). Warm bias in lower troposphere shows strong diurnal variation (larger in daytime). TEST predicts less cloud cover in almost all levels.

18 total cloud low cloudmid cloudhigh cloud downward short wave radiationTsfc Tsfc and cloud cover distribution 48 hour forecast (00 UTC), TEST-CNTL. Correlation can be seen between surface temperature, downward short wave radiation at surface and cloud cover.

19 Based on current operational GFS Box Ferrier scheme Modifications to reduce temperature bias Minimum FLARGE=0.07 (0.1 for 1st experiment) Include precipitating snow in cloud cover calculation Moorthi cloud cover for radiation ncw=900 over land, 150 over ocean (CNTL: ~110) Include suspended convective cloud water in cloud cover calculation for radiation scheme T382L64 resolution Started from Dec. 20, 2009 Control: current operational GFS, T382L64 Experiment design (2nd TEST)

20 CNTL TEST Z500 anomaly correlation

21 Vector wind RMSE (Tropics) Vector wind RMSE Tropics TEST−CNTL Vector wind RMSE of TEST is smaller than that of CNTL in the upper troposphere over the Tropics, but larger in the lower troposphere.

22 Temperature RMSE (NH) Temperature RMSE Northern Hemisphere TEST−CNTL Temperature RMSE of TEST is very large compared to that of CNTL in the lower troposphere over the Northern Hemisphere.

23 CNTL TEST Precipitation score

24 Low cloud cover 48 hour forecast of low cloud cover. Initial time of forecast is 00 UTC 12 July It is possible that excessive low cloud is the cause of the large temperature RMSE in the lower troposphere. Cloud cover used in radiation scheme is calculated from relative humidity and cloud water mixing ratio using formulation by Xu and Randall (1996). Box Ferrier (2nd TEST) Zhao

25 Zhao and Carr (1997) assumed uniform distribution of water contents in cloud part and in clear part. Increasing water vapor is partitioned to existing cloud part, clear part and increasing cloud part assuming RH env =RH crit + C(1−RH crit ). New scheme assumes uniform PDF of total water. Increasing water vapor is used to increase total water in the grid uniformly. RH crit is not needed. The distribution half width is. New PDF cloud parameterization total water x q*q* x cloud cover increasing water vapor q*q* t-1 t-1 t t cloud cover Zhao and Carr (1997) New scheme

26  The Ferrier cloud microphysics scheme used in NCEP NAM was tested for NCEP GFS to replace Zhao and Carr scheme.  Fractional cloud coverage in a grid box is considered.  Cloud water/ice decreased in the upper troposphere and increased in lower troposphere and tropical mid troposphere.  Wind forecast in the tropical upper troposphere is improved. Temperature RMSE in the lower troposphere is worsen due to the excessive low cloud cover.  New cloud cover formulation assuming uniform PDF is under development. Summary

27 q w +q i deficiency in Zhao scheme SCM with Zhao microphysics predicted less cloud water in lower troposphere compared to SCM with Ferrier microphysics. q w + q i Ferrier - Zhao 48 hour forecast by SCM at Porto Santo site. Initial time of forecast is 00 UTC 14 June Ferrier scheme Zhao scheme q w + q i =0

28 Effect of Δt 48 hour forecast of cloud water + cloud ice by SCM at Porto Santo site. Initial time of forecast is 00 UTC 14 June Output from Zhao scheme Δt = 600 sec. Deficiency of cloud water and ice is significant when time step is long. It is due to the excessive conversion from cloud water to precipitation which is calculated explicitly. The excessive conversion results in small cloud water bias in troposphere. Input to Zhao scheme Δt = 60 sec.

29 Explicit scheme (A: conversion rate, A≥0) Simple implicit scheme A(t) is used for simplicity. Implicit scheme

30 Result of implicit scheme 48 hour forecast of cloud water + cloud ice by SCM at Porto Santo site. Initial time of forecast is 00 UTC 14 June The excessive conversion from cloud water to precipitation is reduced by introducing implicit scheme to conversion calculation. Δt = 600 sec., explicit Δt = 60 sec., implicit Δt = 600 sec., implicit Δt = 60 sec., explicit

31 Thank you! Hare-run: JMA ’ s mascot Hare: Japanese word for “fine weather.”

32 Backup Slides

33 Grid is divided to three part (cloudy, clear with precipitation from upper level, clear without precipitation from upper level). Areas and precipitation rates are calculated from those at upper level. Cloud cover is given by Sundqvist et al. (1989) formulation. Maximum overlap is assumed for adjacent level cloud and random overlap is assumed for detached level cloud in the precipitation rate calculation. Ferrier microphysics is executed for cloudy portion and clear w/ precipitation portion. Grid division L+1 L Ferrier scheme CVR(L) < CVR(L+1) CVR(L) > CVR(L+1) L+1 L Ferrier scheme (evap) averaging

34 Based on current operational GFS Box Ferrier scheme T382L64 resolution Started from June 2, 2008 Control: current operational GFS, T382L64 Experiment design (1st TEST)

hPa height anomaly corr. Northern hemisphere Scores TEST CNTL TEST 24-hr fcst 48-hr fcst Vector wind RMSE Tropics TEST−CNTL Temperature fit against radiosonde observation Northern hemisphere Jun. 2, 2008 – Aug. 2, 2008

36 CNTL TEST Precipitation score

37 Based on current operational GFS Box Ferrier scheme Modifications to reduce temperature bias Minimum FLARGE=0.07 (0.1 for 1st experiment) Include precipitating snow in cloud cover calculation Moorthi cloud cover for radiation ncw=900 over land, 150 over ocean (CNTL: ~110) Include suspended convective cloud water in cloud cover calculation for radiation scheme T382L64 resolution Started from Dec. 20, 2009 Control: current operational GFS, T382L64 Experiment design (2nd TEST)

hPa height anomaly corr. Northern hemisphere Scores CNTL Vector wind RMSE Tropics TEST−CNTL Temperature RMSE Northern hemisphere TEST−CNTL TEST Dec. 20, 2009 – Feb

39 Fit to RAOB (2nd TEST) Cold bias in the upper troposphere and warm bias in the lower troposphere over the north America are reduced. CNTL TEST Analysis Guess

40 CNTL TEST (previous TEST +FLARGE+snow+cnvw+Moorti+ncw) Previous TEST Previous TEST +FLARGE+snow Previous TEST +FLARGE+snow+Moorthi Previous TEST +FLARGE+snow+cnvw+ncw Previous TEST+cnvw Low cloud cover

41 Low cloud cover 48 hour forecast of low cloud cover. Initial time of forecast is 00 UTC 12 July It is possible that excessive low cloud is the cause of the large temperature RMSE in the lower troposphere. CNTL 2nd TEST 1st TEST