5 research outputs found
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Understanding global model systematic shortwave radiation errors in subtropical marine boundary layer cloud regimes
Global numerical weather prediction and climate models are subject to longâstanding systematic shortwave radiation errors due to deficiencies in the representation of boundary layer clouds over the ocean. In the subtropics, clouds are typically too reflective in the cumulus regime and not reflective enough in the stratocumulus regime. Potential sources of error include cloud cover, liquid water path, effective radius, and subgrid heterogeneity, but diagnosing the absolute contributions of each to the radiation bias is hampered by uncertainties and sometimes contradictory information from different observational products. This paper draws on a set of shipâbased observations of boundary layer clouds obtained during the ARM MAGIC campaign along a northeast Pacific Ocean transect, crossing both stratocumulus and shallow cumulus cloud regimes. The surfaceâbased observations of cloud properties are compared with various satellite products, taking account of the diurnal cycle, to provide an improved quantitative assessment of the deficiencies in the European Centre for MediumâRange Weather Forecasts global numerical weather prediction model. A series of offâline radiation calculations are then performed to assess the impact on the shortwave radiation bias of correcting each of the model's deficiencies in cloud characteristics along the transect. A reduction in the bias is achieved by improving the agreement between modeled and observed inâcloud liquid water path frequency distributions. In the cumulus regime, this is accomplished primarily by reducing the allâsky water path, while for the stratocumulus regime, an underestimate of cloud cover and liquid water and an overestimate in effective radius and subgrid heterogeneity all contribute to a lack of reflected shortwave radiation
Large-Scale Vertical Velocity, Diabatic Heating and Drying Profiles Associated with Seasonal and Diurnal Variations of Convective Systems Observed in the GoAmazon2014/5 Experiment
This study describes the characteristics of large-scale vertical velocity,
apparent heating source (Q1) and apparent moisture sink
(Q2) profiles associated with seasonal and diurnal variations
of convective systems observed during the two intensive operational periods
(IOPs) that were conducted from 15 February to 26 March 2014 (wet season) and
from 1 September to 10 October 2014 (dry season) near Manaus, Brazil, during
the Green Ocean Amazon (GoAmazon2014/5) experiment. The derived large-scale
fields have large diurnal variations according to convective activity in the
GoAmazon region and the morning profiles show distinct differences between
the dry and wet seasons. In the wet season, propagating convective systems
originating far from the GoAmazon region are often seen in the early morning,
while in the dry season they are rarely observed. Afternoon convective
systems due to solar heating are frequently seen in both seasons.
Accordingly, in the morning, there is strong upward motion and associated
heating and drying throughout the entire troposphere in the wet season, which
is limited to lower levels in the dry season. In the afternoon, both seasons\ud
exhibit weak heating and strong moistening in the boundary layer related to
the vertical convergence of eddy fluxes. A set of case studies of three
typical types of convective systems occurring in Amazonia â i.e.,
locally occurring systems, coastal-occurring systems and basin-occurring
systems â is also conducted to investigate the variability of the
large-scale environment with different types of convective systems