HIGHLIGHTED RESULTS FOR FIRE II

FIRE has made significant progress in all of the areas critical to understanding the roles of clouds in the climate system.

For example:

• For global observations, FIRE has defined the accuracy of ISCCP cloud amount, height, and optical depth for many of the earth's cloud systems, especially critical cirrus and boundary layer cloud. FIRE has also shown how to improve the accuracy of cirrus optical depths and heights, along with stratus heights for the next version of ISCCP. Overall, the conclusion is that ISCCP is more accurate by far than any current global climate model, and that the ISCCP data can be used by modelers for critical cloud radiation verification. FIRE has also demonstrated new capabilities for satellites to remotely sense cloud particle size and phase. FIRE research has greatly impacted the spatial resolution and spectral channel selection for the MODIS instruments: the next generation satellite cloud radiometer and arguably the first instrument including accurate and stable calibration designed to quantitatively measure key cloud properties.

• For cloud microphysics and radiation, FIRE has finally opened Pandora's box: what do we do for ice crystal clouds? FIRE uncovered the importance of small ice crystals for cirrus radiative effects, defined a new set of questions to be answered, showed the great superiority of hexagonal crystal scattering phase functions over spheres for a wide variety of cirrus cloud cases and independent instrument measurement tests, and defined the need for new ice particle instruments and funded their further development. Although FIRE has not answered all cirrus ice questions, or removed all uncertainties in how to model cirrus, it has greatly reduced the previous uncertainties. For water droplet clouds, FIRE has raised new questions about the reproducibility of FSSP (Forward Scattering Spectrometer Probe) data. At the same time, new optical probes show promise for determining radiative "effective radius" as well as LWC (Liquid Water Content) and extinction coefficient. The next phase of FIRE will incorporate both the old (FSSP, 2D) probes and the new particle probes. FIRE has observed and modeled the effects of CCN concentrations on cloud droplet populations/distributions and the subsequent effects upon the cloud radiative properties.

• Improved flux radiometers were flown on the ER-2 and Sabreliner aircraft and were well-matched to radiometers on the ground, providing a high-quality, full-column description of the radiative fluxes for FIRE Cirrus-II. At the same time, ground-based active sensors (both lidar and radar) as well as the airborne cloud lidar on the ER-2 provided a detailed description of the cloud location, structure, and ice water profile. Coordination between the aircraft and ground-based sensors was much improved in comparison to FIRE Cirrus-I, i.e., greater coincidence. Significant improvements were also made in capabilities for spectral coverage and resolution in comparison to FIRE Cirrus-I. New measurements of the spectral albedo of cirrus clouds were obtained and expanded knowledge of the spectral-dependence cloud radiative properties is anticipated. There is strong potential for significant impacts on future satellite-based cloud observing capabilities

• For cloud dynamics, FIRE has focused on improving cloud scale (such as LES) and mesoscale cloud models to help scientists better simulate and understand the dynamics of these systems. FIRE produced the first detailed simulations of stratocumulus break-up. Through this work, the importance of solar radiation for cloud break-up has been established. The relevance of cloud-top entrainment instability has also been clarified, and new criteria for its onset have been developed. In addition, FIRE has produced the first highly detailed simulations of the interactions of stratocumulus cloud dynamics, aerosol physics, cloud microphysics, and radiative transfer. Again, the breadth of these activities is striking, and their obvious relevance to understanding the role of clouds in climate is great.

• Real time data from ASTEX were furnished to ECMWF for incorporation into the operational forecast model. Operational and research forecast models were employed in the field phases for both marine boundary layer and cirrus layer field campaigns.

• Cloud modeling studies have shown that many of the important physical processes governing the microphysical development and the vertical transport of ice depend strongly on the small-scale dynamical development within cirrus clouds. In turn, radiative processes, that are highly sensitive to the cloud ice mass distribution including macroscopic organization and internal structure, have been shown to significantly regulate cloud dynamical development. These conclusions are supported by the analysis of high-resolution in situ and active remote sensing observations that show the prevalence of mesoscale and small-scale organization within cirrus clouds systems.

• For cloud radiation, FIRE has made progress in several critical areas. Examination of the three dimensional (3-D) nature of boundary layer clouds has shown that at least over ocean, plane parallel radiative transfer theory appears to be adequate as long as the frequency distribution of optical depth is defined. Two unexpected FIRE results are: that Gaussian distributions of cloud optical depth occur only for overcast conditions (on a 60 km scale); and that many, if not most, boundary layer clouds over ocean are not "black" in the thermal infrared.

  Ship tracks have dramatically demonstrated the critical role played by CCN in clouds and their impact on cloud radiative properties (particle size and optical depth). FIRE measurements show the lack of any large "anomalous absorption" in cloud particles and suggest that the remaining discrepancies are likely to be found in water vapor absorption and/or 3-D effects. The recent LOWTRAN 7 version predicts just such an increase in water vapor absorption from far wing line absorption. In addition, a new cloud nephelometer has been developed at the request of FIRE. This should provide better determinations of the asymmetry parameter. New theoretical results and laboratory results are becoming available for non-spherical particle scattering.

• FIRE GCM result highlights include the following: FIRE data enabled the development of empirical relationships between cirrus cloud optical properties and temperature; these relationships are suitable either for direct incorporation into GCMs, or for evaluation of the results from more advanced models that directly predict both cirrus optical properties and temperature. Our improved understanding of the physics of stratocumulus cloud break-up, in terms of solar warming, drizzle, and cloud-top entrainment instability, has led to the development of new parameterizations of the stratocumulus transition. FIRE data are also being used to develop new semi-empirical parameterizations of cloud amount, that will be directly incorporated into at least one GCM in the very near future.

  In addition, FIRE data has helped to convince climate modelers of the importance of cloud-aerosol interactions for determining the macroscopic optical and hydrological properties of the clouds. FIRE GCM results have shown a dramatic sensitivity of the tropical water vapor distribution to upper tropospheric clouds; these results will help guide future FIRE studies of middle and upper tropospheric cloud systems.

• FIRE has nurtured the development, deployment and application of multiple remote sensing systems for observing cloud layer dynamics, microphysics, thermodynamics and radiative properties. The list is extensive and will continue to grow, but currently includes, wind profilers, Doppler- millimeter, infrared and visible - radars/lidars, radio acoustic sounding systems, interferometers and radiometers. FIRE can boast many firsts in the initiation and application of these techniques. Information gleaned from these systems in the future will be critical in improving our understanding of climatically important cloud systems.

• Another significant highlight of the FIRE project, which includes both FIRE-I and FIRE-II, has been the first serious and sustained communication across the microphysical, dynamical, and radiative science communities for both theoretical modeling and observations of clouds. The entire research community has been greatly enriched and educated. Problems are being approached from directions not imagined just a few years ago. FIRE scientists feel as if they are on a race course with many exciting things to look at and not enough time to do them all. Synergism is happening now, not five years after publication, when the data are often too "cold" to go back to for molding into the shape needed by the modeler, or when the expertise critical to proper interpretation of the data has gone off to work on some other problem.