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G. A. Payne, C. A. Friehe, and D. K. Edwards

Abstract

The heat transfer characteristics of an aircraft-mounted resistance-wire atmospheric temperature sensor are modeled to determine the time and frequency responses. The sensor element (Rosemount 102E4AL) consists of a 25-μm-diameter platinum wire wound around a cruciform mica support with approximately 143 diameters of wire between contacts with the mica. A longitudinally distributed, radially lumped capacitance model provided for the convective heat transfer to the wire and the transient heat conduction along it. Similarly, the temperature gradient across the thin dimension of the mica support was neglected, and a radially distributed model provided for the convective heat transfer to the mica and the transient conduction within it. The two solutions are coupled by the boundary conditions at the wire-mica contact. The equations were solved to produce the temperature distribution along the wire and in the mica support as a function of the frequency of a free-stream sinusoidal temperature fluctuation. The frequency response transfer function was determined and fit to a two-time-constant transfer function by regression analysis. The two-time-constant model fits the general solution very well. The small (fast response) time constant is essentially determined by the wire itself. The larger (slow response) time constant is due to conduction into and out of the mica supports. The model predicts that the effects of the mica supports are important for frequencies greater than about 0.1 Hz. The responses to five different temperature waveform inputs (sinusoid, step, pulse, ramp, and ramp level) are derived using the two-time-constant model with Laplace transform techniques for both infinite-length wire (no mica support effects) and the finite-length wire of the 102 probe. The actual temperature signals are distorted by the larger time constant of the mica supports, especially for the pulse and ramp inputs that are typical of aircraft measurements of thermals and inversions.

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C. E. Dorman, T. Holt, D. P. Rogers, and K. Edwards

Abstract

Data from surface stations, profilers, long-range aircraft surveys, and satellites were used to characterize the large-scale structure of the marine boundary layer off of California and Oregon during June and July 1996. To supplement these observations, June–July 1996 averages of meteorological fields from the U.S. Navy’s operational Coupled Ocean–Atmospheric Mesoscale Prediction System (COAMPS) model were generated for the region. Model calculations show a broad band of fast northerly surface winds exceeding 7 m s−1 extending along the California–Oregon coast. Buoy-measured peaks of 7.1 m s−1 off Bodega Bay, 7.2 m s−1 off Point Piedras Blancas, and 8.8 m s−1 near Point Conception were reported. Mean winds at the buoys located 15–25 km offshore are generally faster than those at coastal stations, and all station winds are faster in the afternoon.

The aircraft and station observations confirm that an air temperature inversion typically marks the top of the marine boundary layer, which deepens offshore. Along the coast, the marine boundary layer thins between Cape Blanco and Santa Barbara. The inversion base height is at its lowest (195 m) at Bodega Bay in northern California and at its highest at Los Angeles and San Diego (416 m). The inversion strength is strongest between Bodega Bay and Point Piedras Blancas, exceeding 10.8°C. The June–July 1996 marine boundary layer depth from COAMPS shows a gradual deepening with distance offshore.

The model-averaged flow within the marine boundary layer is supercritical (Froude number > 1) in a region between San Francisco and Cape Mendocino that extends offshore to 126.4°W. Smaller isolated supercritical areas occur in the lee of every major cape, with the peak Froude number of 1.3 in the lee of Cape Mendocino. This is consistent with aircraft flights of Coastal Waves ’96, when extensive regions of supercritical flow off central California and downwind of major capes were recorded with highest Froude numbers around 1.5–2.0. A broad, wedge-shaped area of nearly critical flow (Froude number > 0.8) extends from Cape Blanco to Point Piedras Blancas and offshore to about 128.5°W in the model output.

The model wind stress has a broad maximum exceeding 0.3 N m−2 between Cape Mendocino and San Francisco with the highest values found within 100 km of the coast. Stress calculated directly from low aircraft legs is highest in the lee of large capes with peak values exceeding 0.7 N m−2. Overall aircraft magnitudes are similar to the model’s, but a direct comparison with the 2-month average from the model is not possible due to the lesser space and time coverage of the flights. The stress maxima along the California coast shown in the model results are spatially consistent with the region of coldest sea surface temperature observed by satellite.

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P. L. Fuehrer, C. A. Friehe, and D. K. Edwards

Abstract

No abstract available

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P. L. Fuehrer, C. A. Friehe, and D. K. Edwards

Abstract

An analytical study was conducted of the thermal frequency response of an atmospheric temperature probe consisting of a thermistor bead with two lead wires soldered to thin support posts. Such probes are used in aircraft temperature sensors and for surface-layer turbulence studies. The results show the effects of the lead wires on the frequency response (amplitude and phase) of the probe for two end conditions of the lead wires: 1) fixed temperature at the mean free-stream value, and 2) adiabatic. For the smallest commercially available thermistor bead of approximately 200-µm diameter and for 20-µm-diameter platinum lead-wire lengths of about 0.8 mm, the conduction to the supports was found to be minimal for both end conditions. It was determined, however, that the lead wires themselves act as heat transfer fins and actually improve the frequency response over that of an ideal isolated bead. Model calculations show that the inclusion of multiple lead wires (four and six) connected mechanically, but not electrically or thermally, to supports would further improve the response. The thermal analysis is also applied to small type-E thermocouple junctions made of 12.5-, 25-, and 50-µm- diameter wires, and the results show that the lead wires also improve the frequency response.

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J. M. Haywood, D. L. Roberts, A. Slingo, J. M. Edwards, and K. P. Shine

Abstract

A new radiation code within a general circulation model is used to assess the direct solar and thermal radiative forcing by sulfate aerosol of anthropogenic origin and soot aerosol from fossil-fuel burning. The radiative effects of different aerosol profiles, relative humidity parameterizations, chemical compositions, and internal and external mixtures of the two aerosol types are investigated. The contribution to the radiative forcing from cloudy sky regions is found to be negligible for sulfate aerosol; this is in contrast to recent studies where the cloudy sky contribution was estimated using a method in which the spatial correlation between cloud amount and sulfate burden was ignored. However, the radiative forcing due to fossil-fuel soot aerosol is enhanced in cloudy regions if soot aerosol exists within or above the cloud. The global solar radiative forcing due to sulfate aerosol is estimated to be −0.38 W m−2 and the global thermal radiative forcing is estimated to be +0.01 W m−2. The hemispheric mean radiative forcings vary by only about 10% for reasonable assumptions about the chemical form of the sulfate aerosol and the relative humidity dependence; the uncertainties in the aerosol loading are far more significant. If a soot/sulfate mass ratio of 0.075 is assumed, then the global solar radiative forcing weakens to −0.18 W m−2 for an external mixture and weakens further for an internal mixture. Additionally, the spatial distribution of the radiative forcing shows strong negative/positive forcing contrasts that may influence the dynamical response of the atmosphere. Although these results are extremely sensitive to the adopted soot/sulfate ratio and the assumed vertical profile, they indicate that fossil-fuel soot aerosol may exert a nonnegligible radiative forcing and emphasize the need to consider each anthropogenic aerosol species.

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W. A. Lahoz, V.-H. Peuch, J. Orphal, J.-L. Attié, K. Chance, X. Liu, D. Edwards, H. Elbern, J.-M. Flaud, M. Claeyman, and L. El Amraoui

Air quality (AQ) is defined by the atmospheric composition of gases and particulates near the Earth's surface. This composition depends on local emissions of pollutants, chemistry, and transport processes; it is highly variable in space and time. Key lower-tropospheric pollutants include ozone, aerosols, and the ozone precursors NOx and volatile organic compounds. Information on the transport of pollutants is provided by carbon monoxide measurements. Air quality impacts human society, because high concentrations of pollutants can have adverse effects on human health; health costs attributable to AQ are high. The ability to monitor, forecast, and manage AQ is thus crucial for human society. In this paper we identify the observational requirements needed to undertake this task, discuss the advantages of the geostationary platform for monitoring AQ from space, and indicate important challenges to overcome. We present planned geostationary missions to monitor AQ in Europe, the United States, and Asia, and advocate for the usefulness of such a constellation in addition to the current global observing system of tropospheric composition.

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G.-K. Plattner, R. Knutti, F. Joos, T. F. Stocker, W. von Bloh, V. Brovkin, D. Cameron, E. Driesschaert, S. Dutkiewicz, M. Eby, N. R. Edwards, T. Fichefet, J. C. Hargreaves, C. D. Jones, M. F. Loutre, H. D. Matthews, A. Mouchet, S. A. Müller, S. Nawrath, A. Price, A. Sokolov, K. M. Strassmann, and A. J. Weaver

Abstract

Eight earth system models of intermediate complexity (EMICs) are used to project climate change commitments for the recent Intergovernmental Panel on Climate Change’s (IPCC’s) Fourth Assessment Report (AR4). Simulations are run until the year 3000 a.d. and extend substantially farther into the future than conceptually similar simulations with atmosphere–ocean general circulation models (AOGCMs) coupled to carbon cycle models. In this paper the following are investigated: 1) the climate change commitment in response to stabilized greenhouse gases and stabilized total radiative forcing, 2) the climate change commitment in response to earlier CO2 emissions, and 3) emission trajectories for profiles leading to the stabilization of atmospheric CO2 and their uncertainties due to carbon cycle processes. Results over the twenty-first century compare reasonably well with results from AOGCMs, and the suite of EMICs proves well suited to complement more complex models. Substantial climate change commitments for sea level rise and global mean surface temperature increase after a stabilization of atmospheric greenhouse gases and radiative forcing in the year 2100 are identified. The additional warming by the year 3000 is 0.6–1.6 K for the low-CO2 IPCC Special Report on Emissions Scenarios (SRES) B1 scenario and 1.3–2.2 K for the high-CO2 SRES A2 scenario. Correspondingly, the post-2100 thermal expansion commitment is 0.3–1.1 m for SRES B1 and 0.5–2.2 m for SRES A2. Sea level continues to rise due to thermal expansion for several centuries after CO2 stabilization. In contrast, surface temperature changes slow down after a century. The meridional overturning circulation is weakened in all EMICs, but recovers to nearly initial values in all but one of the models after centuries for the scenarios considered. Emissions during the twenty-first century continue to impact atmospheric CO2 and climate even at year 3000. All models find that most of the anthropogenic carbon emissions are eventually taken up by the ocean (49%–62%) in year 3000, and that a substantial fraction (15%–28%) is still airborne even 900 yr after carbon emissions have ceased. Future stabilization of atmospheric CO2 and climate change requires a substantial reduction of CO2 emissions below present levels in all EMICs. This reduction needs to be substantially larger if carbon cycle–climate feedbacks are accounted for or if terrestrial CO2 fertilization is not operating. Large differences among EMICs are identified in both the response to increasing atmospheric CO2 and the response to climate change. This highlights the need for improved representations of carbon cycle processes in these models apart from the sensitivity to climate change. Sensitivity simulations with one single EMIC indicate that both carbon cycle and climate sensitivity related uncertainties on projected allowable emissions are substantial.

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J. E. Kay, C. Deser, A. Phillips, A. Mai, C. Hannay, G. Strand, J. M. Arblaster, S. C. Bates, G. Danabasoglu, J. Edwards, M. Holland, P. Kushner, J.-F. Lamarque, D. Lawrence, K. Lindsay, A. Middleton, E. Munoz, R. Neale, K. Oleson, L. Polvani, and M. Vertenstein

Abstract

While internal climate variability is known to affect climate projections, its influence is often underappreciated and confused with model error. Why? In general, modeling centers contribute a small number of realizations to international climate model assessments [e.g., phase 5 of the Coupled Model Intercomparison Project (CMIP5)]. As a result, model error and internal climate variability are difficult, and at times impossible, to disentangle. In response, the Community Earth System Model (CESM) community designed the CESM Large Ensemble (CESM-LE) with the explicit goal of enabling assessment of climate change in the presence of internal climate variability. All CESM-LE simulations use a single CMIP5 model (CESM with the Community Atmosphere Model, version 5). The core simulations replay the twenty to twenty-first century (1920–2100) 30 times under historical and representative concentration pathway 8.5 external forcing with small initial condition differences. Two companion 1000+-yr-long preindustrial control simulations (fully coupled, prognostic atmosphere and land only) allow assessment of internal climate variability in the absence of climate change. Comprehensive outputs, including many daily fields, are available as single-variable time series on the Earth System Grid for anyone to use. Early results demonstrate the substantial influence of internal climate variability on twentieth- to twenty-first-century climate trajectories. Global warming hiatus decades occur, similar to those recently observed. Internal climate variability alone can produce projection spread comparable to that in CMIP5. Scientists and stakeholders can use CESM-LE outputs to help interpret the observational record, to understand projection spread and to plan for a range of possible futures influenced by both internal climate variability and forced climate change.

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J. Fishman, L. T. Iraci, J. Al-Saadi, K. Chance, F. Chavez, M. Chin, P. Coble, C. Davis, P. M. DiGiacomo, D. Edwards, A. Eldering, J. Goes, J. Herman, C. Hu, D. J. Jacob, C. Jordan, S. R. Kawa, R. Key, X. Liu, S. Lohrenz, A. Mannino, V. Natraj, D. Neil, J. Neu, M. Newchurch, K. Pickering, J. Salisbury, H. Sosik, A. Subramaniam, M. Tzortziou, J. Wang, and M. Wang

The Geostationary Coastal and Air Pollution Events (GEO-CAPE) mission was recommended by the National Research Council's (NRC's) Earth Science Decadal Survey to measure tropospheric trace gases and aerosols and coastal ocean phytoplankton, water quality, and biogeochemistry from geostationary orbit, providing continuous observations within the field of view. To fulfill the mandate and address the challenge put forth by the NRC, two GEO-CAPE Science Working Groups (SWGs), representing the atmospheric composition and ocean color disciplines, have developed realistic science objectives using input drawn from several community workshops. The GEO-CAPE mission will take advantage of this revolutionary advance in temporal frequency for both of these disciplines. Multiple observations per day are required to explore the physical, chemical, and dynamical processes that determine tropospheric composition and air quality over spatial scales ranging from urban to continental, and over temporal scales ranging from diurnal to seasonal. Likewise, high-frequency satellite observations are critical to studying and quantifying biological, chemical, and physical processes within the coastal ocean. These observations are to be achieved from a vantage point near 95°–100°W, providing a complete view of North America as well as the adjacent oceans. The SWGs have also endorsed the concept of phased implementation using commercial satellites to reduce mission risk and cost. GEO-CAPE will join the global constellation of geostationary atmospheric chemistry and coastal ocean color sensors planned to be in orbit in the 2020 time frame.

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Nirnimesh Kumar, James A. Lerczak, Tongtong Xu, Amy F. Waterhouse, Jim Thomson, Eric J. Terrill, Christy Swann, Sutara H. Suanda, Matthew S. Spydell, Pieter B. Smit, Alexandra Simpson, Roland Romeiser, Stephen D. Pierce, Tony de Paolo, André Palóczy, Annika O’Dea, Lisa Nyman, James N. Moum, Melissa Moulton, Andrew M. Moore, Arthur J. Miller, Ryan S. Mieras, Sophia T. Merrifield, Kendall Melville, Jacqueline M. McSweeney, Jamie MacMahan, Jennifer A. MacKinnon, Björn Lund, Emanuele Di Lorenzo, Luc Lenain, Michael Kovatch, Tim T. Janssen, Sean R. Haney, Merrick C. Haller, Kevin Haas, Derek J. Grimes, Hans C. Graber, Matt K. Gough, David A. Fertitta, Falk Feddersen, Christopher A. Edwards, William Crawford, John Colosi, C. Chris Chickadel, Sean Celona, Joseph Calantoni, Edward F. Braithwaite III, Johannes Becherer, John A. Barth, and Seongho Ahn

Abstract

The inner shelf, the transition zone between the surfzone and the midshelf, is a dynamically complex region with the evolution of circulation and stratification driven by multiple physical processes. Cross-shelf exchange through the inner shelf has important implications for coastal water quality, ecological connectivity, and lateral movement of sediment and heat. The Inner-Shelf Dynamics Experiment (ISDE) was an intensive, coordinated, multi-institution field experiment from September–October 2017, conducted from the midshelf, through the inner shelf, and into the surfzone near Point Sal, California. Satellite, airborne, shore- and ship-based remote sensing, in-water moorings and ship-based sampling, and numerical ocean circulation models forced by winds, waves, and tides were used to investigate the dynamics governing the circulation and transport in the inner shelf and the role of coastline variability on regional circulation dynamics. Here, the following physical processes are highlighted: internal wave dynamics from the midshelf to the inner shelf; flow separation and eddy shedding off Point Sal; offshore ejection of surfzone waters from rip currents; and wind-driven subtidal circulation dynamics. The extensive dataset from ISDE allows for unprecedented investigations into the role of physical processes in creating spatial heterogeneity, and nonlinear interactions between various inner-shelf physical processes. Overall, the highly spatially and temporally resolved oceanographic measurements and numerical simulations of ISDE provide a central framework for studies exploring this complex and fascinating region of the ocean.

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