Synoptic and Local Influences on a Summertime, Long-Lived, Mixed-Phase Cloud Event Over Summit, Greenland

Long-lived, Arctic mixed-phase clouds play a crucial role in modulating the surface energy balance over the Greenland Ice Sheet. However, due to temporally and spatially inconsistent observations, little is known about the mechanisms that cause their longevity. A persistent, single-layer, mixed-phase cloud was observed from 20-24 July 2012 at the “Integrated Characterization of Energy, Clouds, Atmospheric state, and Precipitation at Summit” (ICECAPS) cloud-atmosphere observatory in Summit Station, Greenland. The hypothesis in this study is motivated by \citet{morrison2012resilience}; this study investigates the hypothesis that local processes promote a cloud’s persistent state, while synoptic-scale processes influence the thermodynamic structure of the lower troposphere. This hypothesis is examined on the 20-24 July 2012 ICECAPS cloud event using the Weather Research and Forecasting model with polar modifications (Polar WRF) in a series of controlled experiments. First, the role of the synoptic-scale processes is examined by fixing the boundary conditions to isolate the influence of the large-scale flow. Westerly winds over western Greenland and easterly winds over eastern Greenland, driven by a surface cyclone off southeastern Greenland, causes flow to converge atop the ice sheet, converse of the usual state due to the katabatic winds. This deeper vertical motion leads to the formation of ice rather that liquid water, leading to cloud dissipation. In the wake of the surface cyclone and moisture boundary, colder, drier air advects over Summit resulting in a very different thermodynamic profile in the boundary layer inhibiting the cloud from reforming. Second, the role of local-scale processes is examined. An experimental simulation investigating the sensitivity of the cloud to its microphysics shows the cloud liquid water mixing ratio (cloud liquid water content) is sensitive to the ice mixing ratio. For lower ice mixing ratios, the cloud liquid water content is higher as a result of a less effective Wegner-Bergeron-Findeisen process. Another experiment looking at the sensitivity of the simulated cloud to the choice of planetary boundary layer scheme reveals that deeper mixing by larger eddies in the boundary layer is important for cloud maintenance. Finally, the role of local processes is examined by modifying the cloud radiative forcings. In all simulations, the cloud forms at the surface as a result of strong surface radiative cooling under a surface-based inversion. Once the cloud forms, the radiative regime changes as there is now emission from the liquid water resulting in cloud-top longwave radiative cooling. This drives buoyancy-driven updrafts that elevate the cloud and result in two feedbacks: one, condensation of moist air near the surface maintaining the cloud liquid water and cloud-top longwave radiative cooling and two, a well-mixed layer that couples the cloud with the surface which maintains the cloud through moisture and energy contributions from the surface fluxes. The surface fluxes are also greater in the presence of the cloud as a result of the increased downwelling longwave flux at the surface from the cloud. As the strength of the cloud-top longwave radiative cooling is determined strongly by the cloud liquid water content, there exists a minimum amount of liquid water to drive strong enough cloud-top cooling and induced buoyancy-driven updrafts needed to one, maintain the cloud and two, elevate it from the surface. There is also a point where increasing the liquid water does not strengthen the above described processes. In addition, shortwave radiation does not significantly impact the cloud maintenance. However, there is some impact on the liquid content of the cloud; this can affect the amount of cloud-top longwave radiative cooling and its induced processes

Earth resources: A continuing bibliography with indexes (issue 61)

This bibliography lists 606 reports, articles, and other documents introduced into the NASA scientific and technical information system between January 1 and March 31, 1989. Emphasis is placed on the use of remote sensing and geophysical instrumentation in spacecraft and aircraft to survey and inventory natural resources and urban areas. Subject matter is grouped according to agriculture and forestry, environmental changes and cultural resources, geodesy and cartography, geology and mineral resources, oceanography and marine resources, hydrology and water management, data processing and distribution systems, and instrumentation and sensors, and economic analysis

NASA earth science and applications division: The program and plans for FY 1988-1989-1990

Described here are the Division's research goals, priorities and emphases for the next several years and an outline of longer term plans. Included are highlights of recent accomplishments, current activities in FY 1988, research emphases in FY 1989, and longer term future plans. Data and information systems, the Geodynamics Program, the Land Processes Program, the Oceanic Processes Program, the Atmospheric Dynamics and Radiation Program, the Atmospheric Chemistry Program, and space flight programs are among the topic covered

Observing and modelling the impact of arctic and tropical cirrus clouds on far-infrared radiance spectra

The work described in this thesis concerns the effect of cirrus clouds on far-infrared (FIR) radiance spectra. Though the importance of both FIR radiation and cirrus clouds to the Earth’s energy budget is well recognised, few high spectral resolution measurements have been made at FIR wavelengths to date. Observations taken during two diverse field campaigns, along with spectra simulated using a radiative transfer model, are used here to investi- gate the FIR signature of cirrus. The FIR observations presented are made using the TAFTS spectrometer, which measures spectral radiances from ei- ther an aircraft or the ground. The deployment of TAFTS during the RHUBC campaign based in Barrow, Alaska is described. TAFTS was used to make ground-based FIR observations of the arctic atmosphere, both with and without cirrus. Comparing these with modelled spectra, which assume a parameterised particle size distribution (PSD) when describing the cirrus microphysics, suggested that the PSD parameterisation underestimates the fraction of ice water content contributed by small ice crystals. This conclusion is corroborated by AERI-ER observations made simultaneously at the Barrow site during RHUBC. TAFTS observations of convective tropical cirrus made during EMERALD- II near Darwin, Australia are also presented here. During EMERALD-II TAFTS was deployed on an aircraft, enabling spectral measurements of cirrus at wavenumbers between 100 and 200cm−1 to be made for the first time. Comparisons with LBLDIS spectra calculated using PSDs measured using cloud probes indicate that the number of small crystals measured may be too high by a factor of three. This result is in agreement with previous studies suggesting that small crystal populations are over-counted by in-situ cloud probes, due to shattering of larger crystals on the probe inlets. The results from both campaigns illustrate the sensitivity of FIR radiances to cirrus properties, with particular emphasis on the effect of small ice crystals

Pre-Aerosol, Clouds, and Ocean Ecosystem (PACE) Mission Science Definition Team Report

We live in an era in which increasing climate variability is having measurable impact on marine ecosystems within our own lifespans. At the same time, an ever-growing human population requires increased access to and use of marine resources. To understand and be better prepared to respond to these challenges, we must expand our capabilities to investigate and monitor ecological and bio geo chemical processes in the oceans. In response to this imperative, the National Aeronautics and Space Administration (NASA) conceived the Pre-Aerosol, Clouds, and ocean Ecosystem (PACE) mission to provide new information for understanding the living ocean and for improving forecasts of Earth System variability. The PACE mission will achieve these objectives by making global ocean color measurements that are essential for understanding the carbon cycle and its inter-relationship with climate change, and by expanding our understanding about ocean ecology and biogeochemistry. PACE measurements will also extend ocean climate data records collected since the 1990s to document changes in the function of aquatic ecosystems as they respond to human activities and natural processes over short and long periods of time. These measurements are pivotal for differentiating natural variability from anthropogenic climate change effects and for understanding the interactions between these processes and various human uses of the ocean. PACE ocean science goals and measurement capabilities greatly exceed those of our heritage ocean color sensors, and are needed to address the many outstanding science questions developed by the oceanographic community over the past 40 years

Laboratory for Atmospheres 2010 Technical Highlights

The 2010 Technical Highlights describes the efforts of all members of the Laboratory for Atmospheres. Their dedication to advancing Earth Science through conducting research, developing and running models, designing instruments, managing projects, running field campaigns, and numerous other activities, is highlighted in this report