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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
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)
3
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
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 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.
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 microphysicsFerrier microphysics Ferrier microphysics Ferrier microphysics (evaporation, melting(evaporation, melting
))
Cloudy Clear 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*
t-1t-1
Schematic distribution of water vapor in grid.
qvq*
t-1t-1
PDF of water vapor in grid.
critRH
RHC
1
11
1/(2 )
*1 qRH critcloud coversuper-saturated
water vapor
tt
tt
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*
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
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 (qv
, qw, qi,…)
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 2009.
Box FerrierBox FerrierZhaoZhao
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 2010.
Box FerrierBox FerrierZhaoZhao
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 RMSETropics
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 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.
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 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.
18
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.
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 RMSETropics
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 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
24
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
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 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
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
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
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 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.
29
• 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
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 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
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 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
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)
35
500 hPa height anomaly corr. Northern hemisphere
Scores
TESTCNTL
CNTL
TEST
24-hr fcst
48-hr fcst
Vector wind RMSETropics
TEST−CNTL
Temperature fit against radiosonde observationNorthern hemisphere
Jun. 2, 2008 – Aug. 2, 2008
36CNTL
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)
38
500 hPa height anomaly corr. Northern hemisphere
Scores
CNTL
Vector wind RMSETropics
TEST−CNTL
TemperatureRMSENorthern hemisphere
TEST−CNTL
TEST
Dec. 20, 2009 – Feb. 28 2010
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
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
41
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
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