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Mark A. Bourassa, Sarah T. Gille, Cecilia Bitz, David Carlson, Ivana Cerovecki, Carol Anne Clayson, Meghan F. Cronin, Will M. Drennan, Chris W. Fairall, Ross N. Hoffman, Gudrun Magnusdottir, Rachel T. Pinker, Ian A. Renfrew, Mark Serreze, Kevin Speer, Lynne D. Talley, and Gary A. Wick

High latitudes present extreme conditions for the measurement and estimation of air–sea and ice fluxes, limiting understanding of related physical processes and feedbacks that are important elements of the Earth's climate. High-latitude climate change can manifest itself in astonishing ways. Arctic sea ice extent at the end of the melt season in September is declining at a mean rate of 12% per decade, with record seasonal minima in 2007 and 2012 ( Comiso et al. 2008 ; Shawstack 2012 ). In 2001

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Xuhui Lee, Shoudong Liu, Wei Xiao, Wei Wang, Zhiqiu Gao, Chang Cao, Cheng Hu, Zhenghua Hu, Shuanghe Shen, Yongwei Wang, Xuefa Wen, Qitao Xiao, Jiaping Xu, Jinbiao Yang, and Mi Zhang

atmospheric carbon ( Cole et al. 1994 ). Lakes are also sources of atmospheric CH 4 ( Bastviken et al. 2011 ) and N 2 O ( Huttunen et al. 2003 ). Eddy covariance (EC) is an in situ technique for measuring momentum, heat, water, and greenhouse gas fluxes. It determines the flux continuously and nonintrusively from simultaneous measurements, in the atmospheric surface layer, of turbulent fluctuations in the air velocity and the scalar quantity of interest. The method is a key measurement tool deployed by

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J. C. Doran, F. J. Barnes, R. L. Coulter, T. L. Crawford, D. D. Baldocchi, L. Balick, D. R. Cook, D. Cooper, R. J. Dobosy, W. A. Dugas, L. Fritschen, R. L. Hart, L. Hipps, J. M. Hubbe, W. Gao, R. Hicks, R. R. Kirkham, K. E. Kunkel, T. J. Martin, T. P. Meyers, W. Porch, J. D. Shannon, W. J. Shaw, E. Swiatek, and C. D. Whiteman

A field campaign was carried out near Boardman, Oregon, to study the effects of subgrid-scale variability of sensible- and latent-heat fluxes on surface boundary-layer properties. The experiment involved three U.S. Department of Energy laboratories, one National Oceanic and Atmospheric Administration laboratory, and several universities. The experiment was conducted in a region of severe contrasts in adjacent surface types that accentuated the response of the atmosphere to variable surface forcing. Large values of sensible-heat flux and low values of latent-heat flux characterized a sagebrush steppe area; significantly smaller sensible-heat fluxes and much larger latent-heat fluxes were associated with extensive tracts of irrigated farmland to the north, east, and west of the steppe. Data were obtained from an array of surface flux stations, remote-sensing devices, an instrumented aircraft, and soil and vegetation measurements. The data will be used to address the problem of extrapolating from a limited number of local measurements to area-averaged values of fluxes suitable for use in global climate models.

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M. G. McPhee, S. F. Ackley, P. Guest, B. A. Huber, D. G. Martinson, J. H. Morison, R. D. Muench, L. Padman, and T. P. Stanton

In winter the eastern Weddell Sea in the Atlantic sector of the Southern Ocean hosts some of the most dynamic air–ice–sea interactions found on earth. Sea ice in the region is kept relatively thin by heat flux from below, maintained by upper-ocean stirring associated with the passage of intense, fast-moving cyclones. Ocean stratification is so weak that the possibility of deep convection exists, and indeed, satellite imagery from the Weddell Sea in the 1970s shows a large expanse of open water (the Weddell Polynya) that persisted through several seasons and may have significantly altered global deep-water production. Understanding what environmental conditions could again trigger widespread oceanic overturn may thus be an important key in determining the role of high latitudes in deep-ocean ventilation and global atmospheric warming. During the Antarctic Zone Flux Experiment in July and August 1994, response of the upper ocean and its ice cover to a series of storms was measured at two drifting stations supported by the National Science Foundation research icebreaker Nathaniel B. Palmer. This article describes the experiment, in which fluxes of heat, mass, and momentum were measured in the upper ocean, sea ice, and lower-atmospheric boundary layer. Initial results illustrate the importance of oceanic heat flux at the ice undersurface for determining the character of the sea ice cover. They also show how the heat flux depends both on high levels of turbulent mixing during intermittent storm events and on large variability in the stratified upper ocean below the mixed layer.

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Jean-Claude André, Jean-Paul Goutorbe, and Alain Perrier

HAPEX~MOBILHY: A HydrologicAtmospheric Experiment for the Studyof Water Budget and Evaporation Fluxat the Climatic Scale Jean-Claude Andr6~,Jean-Paul Goutorbe~, and Alain Perrier2AbstractThe HAPEX-MOBILHY program is aimed at studying the hydrological budget and evaporation flux at the scale ofa GCM (generalcirculation model) grid square, i.e., 10~ km~. Different surface andsubsurface networks will be operated during the year 1986, tomeasure and monitor soil moisture, surface-energy budget

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M. Segal and R.W. Arritt

Significant spatial heterogeneities of daytime surface sensible heat flux are common over land within mesoscale domains. Thermally induced circulations, similar to the sea/lake breeze [termed nonclassical mesoscale circulations (NCMCs)], are anticipated in these situations. Growing research interest in NCMCs has developed in the recent decade. In this article, general quantifications of NCMC characteristics are sun/eyed based on modeling and observational studies, along with further elaborations on specific NCMCs.

The numerical modeling studies have indicated NCMCs with intensity comparable to the sea breeze in the ideal situations of sharp contrast between extended wet soil or crop and adjacent dry land areas. Similar results were obtained when contrasts of cloud with clear sky and snow with snow-free areas were considered. For less ideal contrasts, as well as for thermal contrasts generated by some other types of forcing, weaker NCMCs were simulated.

The limited observational studies have suggested that, for some potential NCMC situations, noticeable horizontal thermal gradients are produced within the lower atmosphere. In general, however, pronounced NCMC flows have not been indicated with great certainty. In many of the potential NCMC situations, the small sizes of the areas in which sensible heat flux is modified compared with the surrounding areas suggest reduced intensity of circulations in the real world, particularly in the presence of an opposing background flow. Additionally, nonuniformity of the surface sensible heat fluxes in one or both of the contrasting surfaces is likely to be an important factor in reducing the real-world intensity of NCMCs. It is concluded that emphasis on observations is essential for further progress in quantification of real-world NCMCs.

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Lisan Yu and Robert A. Weller

A 25-yr (1981–2005) time series of daily latent and sensible heat fluxes over the global ice-free oceans has been produced by synthesizing surface meteorology obtained from satellite remote sensing and atmospheric model reanalyses outputs. The project, named Objectively Analyzed Air–Sea Fluxes (OAFlux), was developed from an initial study of the Atlantic Ocean that demonstrated that such data synthesis improves daily flux estimates over the basin scale. This paper introduces the 25-yr heat flux analysis and documents variability of the global ocean heat flux fields on seasonal, interannual, decadal, and longer time scales suggested by the new dataset.

The study showed that, among all the climate signals investigated, the most striking is a long-term increase in latent heat flux that dominates the data record. The globally averaged latent heat flux increased by roughly 9 W m−2 between the low in 1981 and the peak in 2002, which amounted to about a 10% increase in the mean value over the 25-yr period. Positive linear trends appeared on a global scale, and were most significant over the tropical Indian and western Pacific warm pool and the boundary current regions. The increase in latent heat flux was in concert with the rise of sea surface temperature, suggesting a response of the atmosphere to oceanic forcing.

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Thomas P. Charlock and Timothy L. Alberta

Results from a temporally intensive, limited area, radiative transfer model experiment are on-line for investigating the vertical profile of shortwave and longwave radiative fluxes from the surface to the top of the atmosphere (TOA). The CERES/ARM/GEWEX Experiment (CAGEX) Version 1 provides a record of fluxes that have been computed with a radiative transfer code; the atmospheric sounding, aerosol, and satellite-retrieved cloud data on which the computations have been based; and surface-based measurements of radiative fluxes and cloud properties from ARM for comparison.

The computed broadband fluxes at TOA show considerable scatter when compared with fluxes that are inferred empirically from narrowband operational satellite data. At the surface, LW fluxes computed with an alternate sounding dataset compare well with pyrgeometer measurements. In agreement with earlier work, the authors find that the calculated SW surface insolation is larger than the measurements for clear-sky and total-sky conditions.

This experiment has been developed to test retrievals of radiative fluxes and the associated forcings by clouds, aerosols, surface properties, and water vapor. Collaboration is sought; the goal is to extend the domain of meteorological conditions for which such retrievals can be done accurately. CAGEX Version 1 covers April 1994. Subsequent versions will (a) at first span the same limited geographical area with data from October 1995, (b) then expand to cover a significant fraction of the GEWEX Continental-Scale International Project region for April 1996 through September 1996, and (c) eventually be used in a more advanced form to validate CERES.

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J. A. Curry, C. A. Clayson, W. B. Rossow, R. Reeder, Y.-C. Zhang, P. J. Webster, G. Liu, and R.-S. Sheu

An integrated approach is presented for determining from several different satellite datasets all of the components of the tropical sea surface fluxes of heat, freshwater, and momentum. The methodology for obtaining the surface turbulent and radiative fluxes uses physical properties of the atmosphere and surface retrieved from satellite observations as inputs into models of the surface turbulent and radiative flux processes. The precipitation retrieval combines analysis of satellite microwave brightness temperatures with a statistical model employing satellite observations of visible/infrared radiances. A high-resolution dataset has been prepared for the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE) intensive observation period (IOP), with a spatial resolution of 50 km and temporal resolution of 3 h. The high spatial resolution is needed to resolve the diurnal and mesoscale storm-related variations of the fluxes. The fidelity of the satellite-derived surface fluxes is examined by comparing them with in situ measurements obtained from ships and aircraft during the TOGA COARE IOP and from vertically integrated budgets of heat and freshwater for the atmosphere and ocean. The root-mean-square differences between the satellite-derived and in situ fluxes are dominated by limitations in the satellite sampling; these are reduced when some averaging is done, particularly for the precipitation (which is from a statistical algorithm) and the surface solar radiation (which uses spatially sampled satellite pixels). Nevertheless, the fluxes are determined with a useful accuracy, even at the highest temporal and spatial resolution. By compiling the fluxes at such high resolution, users of the dataset can decide whether and how to average for particular purposes. For example, over time, space, or similar weather events.

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Thomas Foken and Steven Oncley

This report summarizes presentations and discussions that occurred at a workshop held in conjunction with the XIXth General Assembly of the European Geophysical Society (EGS) from 22 to 24 April 1994. The purpose of this workshop was to define the state of the art of micrometeorological flux measurements, to identify problem areas, and to define any additional data that must be taken to solve these problems. This workshop was organized in response to a proposal made at the 1993 EGS conference by T. Foken, T. Delany (National Center for Atmospheric Research), S. Oncley, and L. Tsvang (Institute of Atmospheric Physics, Russia) for a new experiment to investigate the problem of the “unclosed” energy balance. Sixty-one scientists from 14 countries participated in the workshop.

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