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PC-06 Abstract

LBA Land-Surface Atmosphere Studies Directed to Forecast Model Improvement

Alan K Betts — Atmospheric Research (US-PI)
Pedro Leite Silva Dias — USP - Universidade de Sao Paulo (SA-PI)
Maria Assunção Faus da Silva Dias — IAG/USP (SA-PI)

ABSTRACT



This project addresses a key objective of LBA, namely to improve the models

of the surface exchange between the tropical forest of Amazonia and the

atmosphere using the LBA meteorological, surface flux and biophysical data

by analyzing LBA data, and by developing improved parameterizations of

the surface energy balance and boundary layer over Amazonia in global weather

forecast models and in the USP forecast model.




The key scientific objective is "Improved parameterization of the surface

energy balance and boundary layer over Amazonia in weather forecast models."

The scientific approach involves data analysis, tailored to identifying

and understanding the physical processes, and also to the development of

process models suitable for incorporation in forecast models. The land

surface processes in operational forecast models can readily be evaluated

against field data, because of their immediate impact on the model forecast

errors for temperature and humidity near the surface, as well as by comparing

the surface energy and water fluxes including precipitation on diurnal

to seasonal time-scales. At the same time their global impact on the model

systematic errors near the surface, in the boundary layer and in the troposphere

can quickly be seen in monthly forecasts, which show the climate drift

of a model against observations.




This project will continue the improvement of weather forecast models

at ECMWF, which has been progressing for about eight years using

data from FIFE, BOREAS and GCIP.  (A complete list of references dealing

with this work is available from the PI on request.)  The PI is also

interacting with Prof. P.L. Silva Dias on the development of the forecast model

system at USP, which uses the RAMS model.  Conceptual results and parametric

models can then be transferred from forecast models to climate models and

more complex earth system models.




Several specific steps are involved. One is the analysis of LBA surface

hydrometeorological data and sounding data from the dry and rainy season

observing periods, as well as the continuous surface data sets.  We are

currently analyzing the data from the Rondonia LBA-WETAMC/TRMM field

phase.  Betts et al. (2001a) uses the wind regimes identified by other LBA

researchers to explore the surface diurnal cycle and the coupling to the

atmosphere using the data collected at the Rondonia pasture site.  Betts et

al. (2001b) deals with the transport of ozone by convective downdrafts at night

at this site.  Silva Dias et al. (2001) is a case study of a convective

band that developed over Rondonia during the WETAMC.  The second step is

the development of improved land-surface models for Amazonia using data from LBA. 

A new tiled land-surface model has been implemented at ECMWF in the operational

model and in the reanalysis [ERA40], and we are exploring its characteristics

over Amazonia.  Betts and Jakob [2001] compares the diurnal cycle of

precipitation and surface thermodynamics in the ECMWF model with that observed

over Rondonia.  We found that precipitation starts about two hours after

sunrise in the model, several hours earlier than observed, because the model

does not simulate well the morning growth of the non-precipitating convective

boundary layer.  For LBA, a third

tool we shall use is studies of the basin-scale hydrology of the ECMWF

model, which has been very successful in interpreting the performance of

the model hydrology for the Mississippi sub-basins of GCIP.  The ability to

do basin integrals on a Gaussian grid derived from the full model at hourly time

resolution is a unique capability of the ECMWF analysis system.  We plan to

do this using the ECMWF reanalysis. 




Figure 1 from Betts et al. (1998b) shows the nine annual cycles

of the energy balance for the Arkansas-Red River basin, plotted from 5-day

average data. The upper curve (solid) is net radiation (RNet) with

fluctuations on the 5-day time scale associated with clouds and precipitation

in the model. RNet is small in mid-winter. The lower curves are

the model latent (LH: light solid) and sensible (SH: dotted)

heat fluxes. Here we see the most interannual variability, which is related

to rainfall and soil water in summer. In 1988, the driest summer, LH

is low and SH is large relative to wetter summers, such as 1986,

1989 or 1992. The LH flux is larger than the SH flux at all

times and it is upward even in winter. It is probable that the winter evaporation

is too high, because of the lack of a seasonal vegetation cycle in the

model.






 







Figure 1.   Average energy balance for the Arkansas-Red

River basin from the ECMWF reanalysis




For LBA, we will add to the ECMWF T-319 operational model diagnostics,

averages for five of the Amazonia sub-basins, as shown in Figure 2,

so we will have basin energy and water balances on an hourly time-scale

for LBA, with the then-current operational model in 1999-2001. Many smaller

basins are shown in this figure (basins courtesy of Tom Dunne and Brad

Newton), but we will onlyanalyze the major sub-basins represented by the

quadrilaterals shown. Precipitation and basin streamflow data will be used

for evaluation of the model on this scale. The eastern basin, labeled 1,

is largely ungauged. Basin 2 is the Madeira, basin 3 (which includes a

smaller sub-basin 5, representing primarily the Purus, Jurua and Jutai)

includes also the Amazonas, Ica and Japura basins. Basin 4 is primarily

the Negro. 














Figure 2. Amazonia sub-basins to be archived at ECMWF for LBA.



References.



Beljaars, A.C.M., P. Viterbo, M.J. Miller and A.K. Betts, 1996: The

anomalous rainfall over the US during July 1993: sensitivity to land surface

parameterization. Mon. Wea. Rev., 124, 362-383.




Betts, A.K., J.H. Ball, and A.C.M. Beljaars, 1993: Comparison between

the land surface response of the European Centre model and the FIFE-1987

data. Quart. J. Roy. Meteor. Soc. , 119, 975-1001.




Betts, A.K., S-Y. Hong and H-L. Pan, 1996a: Comparison of NCEP/NCAR

Reanalysis with 1987 FIFE data. Mon. Wea. Rev., 124, 1480-1498.




Betts, A. K., J.H. Ball, Beljaars, A.C.M., M.J. Miller and P. Viterbo,

1996b: The land-surface-atmosphere interaction: a review based on observational

and global modeling perspectives. J. Geophys. Res. 101, 7209-7225.




Betts, A.K., F. Chen,, K. Mitchell and Z. Janji, 1997: Assessment of

land-surface and boundary layer models in 2 operational versions of the

Eta Model using FIFE data. Mon. Wea. Rev., 125, 2896-2915.




Betts A. K., P. Viterbo and A.C.M. Beljaars, 1998a: Comparison of the

ECMWF reanalysis with the 1987 FIFE data. Mon. Wea. Rev., 126,

186-198.




Betts, A. K., P. Viterbo and E. Wood, 1998b: Surface Energy and water

balance for the Arkansas-Red river basin from the ECMWF reanalysis.

J. Clim
., (in press)




Betts A. K., P. Viterbo, A.C.M. Beljaars, H-L. Pan, S-Y. Hong, M. L.

Goulden and S.C. Wofsy, 1998c: Evaluation of the land-surface interaction

in the ECMWF and NCEP/NCAR reanalyses over grassland (FIFE) and boreal

forest (BOREAS). J. Geophys. Res. (in press).




Betts, A.K., J. Fuentes, M. Garstang, and J.H. Ball M.,

2001a.  Surface diurnal cycle and Boundary Layer structure over Rondonia

during the rainy season.  JGR-Atmospheres (in press).

Betts,

A.K., L.V. Gatti, A.M. Cordova, M.A.F. Silva Dias, and J. Fuentes, 2001b. 

Transport of ozone to the surface by convective downdrafts at night.  JGR-Atmospheres

(in press).

Betts, A.K., and C. Jakob, 2001. 

Evaluation of the diurnal cycle of precipitation, surface thermodynamics and

surface fluxes in the ECMWF model using LBA data.  JGR-Atmospheres

(in press).

Silva Dias, M.A.F., W. Petersen, P.L. Silva

Dias, R. Cifelli, A.K. Betts, M. Longo, A.M. Gomes, G.F. Fisch, M.A. Antonio,

and R.I. Albrecht, 2001.  A case study of convective organization into

precipitating lines in the Southwest Amazon during the WETAMC and TRMM-LBA. 

JGR-Atmospheres (in press).




Dr. Alan K. Betts,


Atmospheric Research


58 Hendee Lane,


Pittsford, VT 05763


ph: (802) 483-2087


fax: (802) 483-6167


akbetts@aol.com



 







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