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Title: Improving Subtropical Boundary Layer Cloudiness in the 2011 NCEP GFS

Abstract

The current operational version of National Centers for Environmental Prediction (NCEP) Global Forecasting System (GFS) shows significant low cloud bias. These biases also appear in the Coupled Forecast System (CFS), which is developed from the GFS. These low cloud biases degrade seasonal and longer climate forecasts, particularly of short-wave cloud radiative forcing, and affect predicted sea surface temperature. Reducing this bias in the GFS will aid the development of future CFS versions and contributes to NCEP's goal of unified weather and climate modelling. Changes are made to the shallow convection and planetary boundary layer parameterisations to make them more consistent with current knowledge of these processes and to reduce the low cloud bias. These changes are tested in a single-column version of GFS and in global simulations with GFS coupled to a dynamical ocean model. In the single-column model, we focus on changing parameters that set the following: the strength of shallow cumulus lateral entrainment, the conversion of updraught liquid water to precipitation and grid-scale condensate, shallow cumulus cloud top, and the effect of shallow convection in stratocumulus environments. Results show that these changes improve the single-column simulations when compared to large eddy simulations, in particular through decreasing the precipitationmore » efficiency of boundary layer clouds. These changes, combined with a few other model improvements, also reduce boundary layer cloud and albedo biases in global coupled simulations.« less

Authors:
; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1167615
Report Number(s):
PNNL-SA-105699
KP1501021
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Geoscientific Model Development, 7(5):2107–2120
Additional Journal Information:
Journal Name: Geoscientific Model Development, 7(5):2107–2120
Country of Publication:
United States
Language:
English

Citation Formats

Fletcher, J. K., Bretherton, Christopher S., Xiao, Heng, Sun, Ruiyu N., and Han, J. Improving Subtropical Boundary Layer Cloudiness in the 2011 NCEP GFS. United States: N. p., 2014. Web. doi:10.5194/gmd-7-2107-2014.
Fletcher, J. K., Bretherton, Christopher S., Xiao, Heng, Sun, Ruiyu N., & Han, J. Improving Subtropical Boundary Layer Cloudiness in the 2011 NCEP GFS. United States. https://doi.org/10.5194/gmd-7-2107-2014
Fletcher, J. K., Bretherton, Christopher S., Xiao, Heng, Sun, Ruiyu N., and Han, J. 2014. "Improving Subtropical Boundary Layer Cloudiness in the 2011 NCEP GFS". United States. https://doi.org/10.5194/gmd-7-2107-2014.
@article{osti_1167615,
title = {Improving Subtropical Boundary Layer Cloudiness in the 2011 NCEP GFS},
author = {Fletcher, J. K. and Bretherton, Christopher S. and Xiao, Heng and Sun, Ruiyu N. and Han, J.},
abstractNote = {The current operational version of National Centers for Environmental Prediction (NCEP) Global Forecasting System (GFS) shows significant low cloud bias. These biases also appear in the Coupled Forecast System (CFS), which is developed from the GFS. These low cloud biases degrade seasonal and longer climate forecasts, particularly of short-wave cloud radiative forcing, and affect predicted sea surface temperature. Reducing this bias in the GFS will aid the development of future CFS versions and contributes to NCEP's goal of unified weather and climate modelling. Changes are made to the shallow convection and planetary boundary layer parameterisations to make them more consistent with current knowledge of these processes and to reduce the low cloud bias. These changes are tested in a single-column version of GFS and in global simulations with GFS coupled to a dynamical ocean model. In the single-column model, we focus on changing parameters that set the following: the strength of shallow cumulus lateral entrainment, the conversion of updraught liquid water to precipitation and grid-scale condensate, shallow cumulus cloud top, and the effect of shallow convection in stratocumulus environments. Results show that these changes improve the single-column simulations when compared to large eddy simulations, in particular through decreasing the precipitation efficiency of boundary layer clouds. These changes, combined with a few other model improvements, also reduce boundary layer cloud and albedo biases in global coupled simulations.},
doi = {10.5194/gmd-7-2107-2014},
url = {https://www.osti.gov/biblio/1167615}, journal = {Geoscientific Model Development, 7(5):2107–2120},
number = ,
volume = ,
place = {United States},
year = {Tue Sep 23 00:00:00 EDT 2014},
month = {Tue Sep 23 00:00:00 EDT 2014}
}