1 Implementation of the Ferrier cloud microphysics scheme in the NCEP GFS Masayuki Nakagawa, Hua-Lu...

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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

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FEATUREZhao & Carr (1997)

[Modified version in GFS]

Ferrier et al. (2002)

[In Eta, WRF option]

Prognosticvariables

Water vapor, cloud condensate (water or ice)

Water vapor, total condensate (cloud water, rain, cloud ice,

snow/graupel/sleet)

Condensationalgorithm

Sundqvist et al. (1989)Asai (1965)

[used in high res models]

Precip fluxesand 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, snowRain, freezing rain,

snow/graupel/sleet (variable rime density for precip ice)

Mixed-phaseconditions

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)

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Flowchart of Ferrier Microphysics

RACW

CloudWater

GROUND

RE

VP

Rain

WaterVapor

RAUT

Sfc Rain

CND

ICN

D

DEP

Sfc Snow/Graupel/Sleet

Cloud Ice

PrecipIce

(Snow/Graupel/

Sleet)

IACWR

IEVP

IACW

IACR

IMLT

New process

T < 0oC T > 0oC

T>0, T<0oC

from Ferrier (2005)

CND Condensation (>0), evaporation (<0) of cloud water

DEP Deposition (>0), sublimation (<0) of ice

REVP Rain evaporationRAUT Autoconversion of

cloud to rainRACW Accretion of cloud

water by rainIMLT Melting of iceIACW Accretion of cloud

water onto iceIACWR Accretion of cloud

water onto ice, liquid water shed to form rain

IACR Freezing of rain to form ice, represented by multiple processes in code

ICND Cloud water condensation onto melting ice, shed to form rain

IEVP Evaporation from wet melting ice

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Water vapor (qv), total condensate (qt) advected in model

Cloud water (qw), rain (qr), cloud ice (qi), precip ice (“snow”, qs) calculated in microphysics

Local, saved arrays store fraction of condensate in form of ice (Fi), fraction of liquid in form of rain (Fr) and fraction of ice in form of precip ice (Fs). Assumed fixed with time in column between microphysics calls. Note that 0 Fi , Fr , Fs 1 .

qt = qw + qr + qi + qs , qice = qi + qs

Fi = qice/qt , Fr = qr/(qw + qr) , Fs = qs/qice

Deriving hydrometeors from total condensate

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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 FerrierConsider fractional cloud coverage in a grid box.Each grid box is divided into three parts.Ferrier microphysics scheme is applied separatel

y to the cloudy and clear with precipitation portion of the grid.

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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 microphysicsFerrier microphysics Ferrier microphysics Ferrier microphysics (evaporation, melting(evaporation, melting

))

Cloudy Clear with precipitation

Clear w/o precipitation

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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*

t-1t-1

Schematic distribution of water vapor in grid.

qvq*

t-1t-1

PDF of water vapor in grid.

critRH

RHC

1

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1/(2 )

*1 qRH critcloud coversuper-saturated

water vapor

tt

tt

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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*

t-1t-1

Schematic distribution of water vapor in grid.

qvq*

t-1t-1

PDF of water vapor in grid.

1/(2 )

tt

cloud coversub-saturated water vapor

tt

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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 (qv

, qw, qi,…)

Ferrier microphysics (cloudy, clear w/ precip. portion)

Grid averaging

Flowchart of box Ferrier scheme

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Cloud condensate forecast

48 hour forecast of zonal mean cloud water + cloud ice. Initial time of forecast is 00 UTC 12 June 2009.

Box FerrierBox FerrierZhaoZhao

Cloud water/ice decreased in the upper troposphere and increased in the lower troposphere and the tropical mid troposphere.

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Precipitation forecast

36 hour forecast of 24 hour accumulated precipitation. Initial time of forecast is 00 UTC 05 February 2010.

Box FerrierBox FerrierZhaoZhao

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• Based on current operational GFS

• Box Ferrier scheme

• T382L64 resolution

• Started from June 2, 2008

• Control: current operational GFS, T382L64

Experiment design (1st TEST)

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dropout CNTL

TEST

Z500 anomaly correlation

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Vector wind RMSE (Tropics)

Vector wind RMSETropics

TEST−CNTL

Implementation of the box Ferrier scheme improved vector wind forecast over the Tropics.

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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

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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 2009.

0.10=TEST

0.08

0.07

0.06

0.05

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.

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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 2009. 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.

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total cloud

low cloud mid cloud high 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.

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• 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


• Started from Dec. 20, 2009


Experiment design (2nd TEST)

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CNTL

TEST

Z500 anomaly correlation

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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.

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Temperature RMSE (NH)

Temperature RMSENorthern Hemisphere

TEST−CNTL

Temperature RMSE of TEST is very large compared to that of CNTL in the lower troposphere over the Northern Hemisphere.

23CNTL

TEST

Precipitation score

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Low cloud cover

48 hour forecast of low cloud cover. Initial time of forecast is 00 UTC 12 July 2009.

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)Box Ferrier (2nd TEST)ZhaoZhao

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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 RHenv=RHcrit + C(1−RHcrit).

New scheme assumes uniform PDF of total water. Increasing water vapor is used to increase total water in the grid uniformly. RHcrit is not needed. The distribution half width is .

New PDF cloud parameterization

total water

x

q*

x

cloud cover

increasing water vapor

q*

t-1t-1 t-1t-1

tt tt

increasing water vapor

cloud cover

Zhao and Carr (1997) New scheme

2*vl qqq

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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

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qw +qi deficiency in Zhao scheme

SCM with Zhao microphysics predicted less cloud water in lower troposphere compared to SCM with Ferrier microphysics.

qqww + q + qiiFerrier - ZhaoFerrier - Zhao

48 hour forecast by SCM at Porto Santo site. Initial time of forecast is 00 UTC 14 June 2009.

Ferrier Ferrier schemescheme

Zhao Zhao schemescheme

qqww + q + qii =0 =0

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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 2009.

Output from Zhao schemeOutput from Zhao scheme

ΔΔt t = 600 sec.= 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 schemeInput to Zhao scheme

ΔΔt t = 60 sec.= 60 sec.

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• Explicit scheme (A: conversion rate, A≥0)

• Simple implicit scheme

A(t) is used for simplicity.

Implicit scheme

ttqAq ww

ttA

tqAq

tqtqAq

ww

www

1

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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 2009.

The excessive conversion from cloud water to precipitation is reduced by introducing implicit scheme to conversion calculation.

ΔΔt = 600 sec., explicitt = 600 sec., explicit

ΔΔt = 60 sec., implicitt = 60 sec., implicitΔΔt = 600 sec., implicitt = 600 sec., implicit

ΔΔt = 60 sec., explicitt = 60 sec., explicit

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Thank you!

Hare-run: JMA’s mascot

Hare: Japanese word for “fine weather.”

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Backup Slides

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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 divisionL+1

LFerrier

scheme

Ferrier scheme

CVR(L) < CVR(L+1)

CVR(L) > CVR(L+1)

L+1

LFerrier

scheme

Ferrier scheme

(evap)

(evap)

averaging

averaging

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• Started from June 2, 2008


Experiment design (1st TEST)

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500 hPa height anomaly corr. Northern hemisphere

Scores

TESTCNTL

CNTL

TEST

24-hr fcst

48-hr fcst


TEST−CNTL

Temperature fit against radiosonde observationNorthern hemisphere

Jun. 2, 2008 – Aug. 2, 2008

36CNTL

TEST

Precipitation score

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• 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


• Started from Dec. 20, 2009


Experiment design (2nd TEST)

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500 hPa height anomaly corr. Northern hemisphere

Scores

CNTL


TEST−CNTL

TemperatureRMSENorthern hemisphere

TEST−CNTL

TEST

Dec. 20, 2009 – Feb. 28 2010

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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

40CNTL

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

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Low cloud cover

48 hour forecast of low cloud cover. Initial time of forecast is 00 UTC 12 July 2009.

It is possible that excessive low cloud is the cause of the large temperature RMSE in the lower troposphere.

CNTL

2nd TEST 1st TEST

1 Implementation of the Ferrier cloud microphysics scheme in the NCEP GFS Masayuki Nakagawa, Hua-Lu...

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