CIRRUS COUPLED
CLOUD-RADIATION EXPERIMENT
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AIMS:
Our aim is to understand the link between evolving ice
cloud microphysical properties and the resulting radiative
signatures of the cirrus, at the macrophysical scale,
as seen from a remote sensing platform.
Our objective is through ground breaking cirrus coupled cloud-radiation airborne campaigns
in arctic and mid-latitudes, to obtain for the first time radiation
measurements across the electromagnetic spectrum (visible to sub-mm wavelengths)
together with state-of-the-art cloud microphysics measurements. This exploits
the recent leap in advances in microphysical and radiance data quality. We will
use these unique datasets to test and facilitate improvement to cirrus
scattering models and parameterizations for climate and NWP models. Our goal is
an accurate parameterisation of cirrus optical properties in global climate
modelling and NWP.
Through a radiative closure
experiment, and testing of cirrus scattering models throughout the LW and SW
for the first time, we seek to provide the evidence for a more direct coupling
between cloud physics and radiation, and to show that such schemes can simulate
the measured radiation fields correctly, through a direct link between GCM
prognostic variables and the cirrus optical properties. Such schemes will
represent a paradigm shift in GCM parameterization, as current operational GCMs
rely on linking radiation to cloud physics through diagnosed quantities only.
OBJECTIVES:
1. A radiative closure cirrus
cloud-radiation experiment in northern and mid latitudes.
2. Obtain a well calibrated set of high resolution
radiance measurements throughout the infra-red and visible spectrum, 0.3-125
microns, from above and below and within an extensive layer of well developed cirrus.
3. Characterise the atmospheric column above and below
the cloud layer in terms of humidity distribution, temperature structure and
other key radiatively-active species.
4. Map the ice crystal particle size distribution, habit
types and crystal complexity (including roughness, concavity etc) within the cloud layer, to provide an accurate,
well-constrained, consistent description of the microphysical state.
5. Use derivatives of the macrophysical
and microphysical state, including ice water content and temperature, as input
into state-of-the-art scattering model codes and cirrus parameterisations,
whose output (via a radiative transfer model) will be critically validated against the radiance
measurements throughout the sub-mm, infrared and visible spectrum. Sensitivity
of the predicted radiance to PSD, habit types, aggregate and ensemble models,
crystal complexity will be investigated by reference to the microphysical
datasets.
6. Exploit campaign datasets and constraint of cloud
microphysical and radiative uncertainties in case
studies to facilitate improvement of cirrus scattering models allowing a
self-consistent and physically-based parameterisation of the ice crystal
scattering properties.
7. Through case studies using northern and mid-latitude
campaign datasets, test the ice crystal scattering models and the coupled
cloud-radiation parameterization by running the high-resolution version of the
MO Unified Model (UM) at 1.0km resolution, with a view to incorporating the new
parameterisations into the widely used UM.
Our
results will have impact in cirrus modelling in GCMs, both for numerical
weather prediction (NWP) and climate change, and in remote sensing.
In addition further objectives are to:
8. Conduct a study of the moderating effect of cirrus on
far-IR heating rates by comparing derived heating rates directly from the
far-IR data, and comparing these to models using the
newly-derived scattering properties.
9. Study the spatial variability of the far-IR cirrus radiative signal as a function of the cloud structure, and
determine the impact on precision of the derived cirrus models.
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