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Paynter D.J.,Princeton University | Ramaswamy V.,Geophysical Fluid Dynamics Laboratory
Journal of Geophysical Research: Atmospheres | Year: 2011

Recent measurements of the water vapor continuum have been combined to form an empirical continuum termed the BPS continuum model. This covers the 800 to 7500 cm-1 spectral region for the self continuum and most of the major absorbing spectral regions between 240 and 7300 cm-1 for the foreign continuum. Longwave (i.e., absorption/emission of terrestrial radiation between 1 and 3000 cm-1) and shortwave (i.e., using solar radiation as a source and considering atmospheric absorption between 1000 and 17000 cm-1) line by line (LBL) radiative transfer calculations have been performed for clear-sky conditions in three standard test atmospheres using line data from the HITRAN database. This has allowed BPS to be compared to the commonly used CKD and MT CKD continuum models, in addition to conducting a more detailed investigation of the separate roles of the self and foreign continua than previously provided in the literature. Using uncertainties obtained from multiple experimental studies it has been possible to estimate the upper and lower limits of the effects due to the continuum in many spectral regions. The outgoing longwave radiation in a midlatitude-summer (MLS) atmosphere calculated by all three continuum models agree to within 0.6 Wm-2 with a 1.1 Wm-2 estimated uncertainty. The corresponding values for surface downwelling radiation are 1.3 Wm-2 2.5 Wm-2. For shortwave absorption, the different models agree within 1.0%, with an estimated uncertainty of 1.7%. However, the three models differ in the amount by which the self and foreign continua contribute to shortwave absorption. Copyright 2011 by the American Geophysical Union.

Brody S.R.,Duke University | Lozier M.S.,Duke University | Dunne J.P.,Geophysical Fluid Dynamics Laboratory
Journal of Geophysical Research: Oceans | Year: 2013

Phytoplankton bloom phenology has important consequences for marine ecosystems and fisheries. Recent studies have used remotely sensed ocean color data to calculate metrics associated with the phenological cycle, such as the phytoplankton bloom initiation date, on regional and global scales. These metrics are often linked to physical or biological forcings. Most studies choose one of several common methods for calculating bloom initiation, leading to questions about whether bloom initiation dates calculated with different methods yield comparable results. Here we compare three methods for finding the date of phytoplankton bloom initiation in the North Atlantic: a biomass-based threshold method, a rate of change method, and a cumulative biomass-based threshold method. We use these methods to examine whether the onset of positive ocean-atmosphere heat fluxes coincides with subpolar bloom initiation. In several coherent locations, we find differences in the patterns of bloom initiation created by each method and differences in the synchrony between bloom initiation and positive heat fluxes, which likely indicate various physical processes at play in the study region. We also assess the effect of missing data on the chosen methods. Key PointsDifferent methods of calculating bloom start dates produced different results.Each method identified the bloom as a different part of the chlorophyll cycle.The onset of positive heat fluxes coincides with the phytoplankton bloom. ©2013. American Geophysical Union. All Rights Reserved.

Delsole T.,George Mason University | Delsole T.,Center for Ocean Land Atmosphere Studies | Yang X.,Geophysical Fluid Dynamics Laboratory | Tippett M.K.,International Research Institute for Climate and Society | Tippett M.K.,King Abdulaziz University
Quarterly Journal of the Royal Meteorological Society | Year: 2013

This article proposes a statistical test for whether a multi-model combination with unequal weights has significantly smaller errors than a combination with equal weights. A combination with equal weights includes the case of a no-skill model, in which all weights equal zero, and the multi-model mean, in which all weights equal 1/M, where M is the number of models. The test is applied to seasonal hindcasts of 2 m temperature and precipitation generated by five state-of-the-art coupled atmosphere-ocean models. The hypothesis of equal weights could not be rejected over 75% the globe for temperature and 90% of the land for precipitation, implying that strategies for unequal weighting of forecasts may be of value only over a relatively small fraction of the globe. The fact that the test does not require pre-specifying a specific strategy for weighting forecasts suggests that it should be useful for exploring a wide range of multi-model strategies. © 2012 Royal Meteorological Society.

Heng K.,ETH Zurich | Frierson D.M.W.,University of Washington | Phillipps P.J.,Geophysical Fluid Dynamics Laboratory
Monthly Notices of the Royal Astronomical Society | Year: 2011

Improving upon our purely dynamical work, we present three-dimensional simulations of the atmospheric circulation on Earth-like (exo)planets and hot Jupiters using the Geophysical Fluid Dynamics Laboratory (GFDL)-Princeton Flexible Modelling System (fms). As the first steps away from the dynamical benchmarks of Heng, Menou & Phillipps, we add dual-band radiative transfer and dry convective adjustment schemes to our computational set-up. Our treatment of radiative transfer assumes stellar irradiation to peak at a wavelength shorter than and distinct from that at which the exoplanet re-emits radiation ('shortwave' versus 'longwave'), and also uses a two-stream approximation. Convection is mimicked by adjusting unstable lapse rates to the dry adiabat. The bottom of the atmosphere is bounded by a uniform slab with a finite thermal inertia. For our models of hot Jupiter, we include an analytical formalism for calculating temperature-pressure profiles, in radiative equilibrium, which accounts for the effect of collision-induced absorption via a single parameter. We discuss our results within the context of the following: the predicted temperature-pressure profiles and the absence/presence of a temperature inversion; the possible maintenance, via atmospheric circulation, of the putative high-altitude, shortwave absorber expected to produce these inversions; the angular/temporal offset of the hotspot from the substellar point, its robustness to our ignorance of hyperviscosity and hence its utility in distinguishing between different hot Jovian atmospheres; and various zonal-mean flow quantities. Our work bridges the gap between three-dimensional simulations which are purely dynamical and those which incorporate multiband radiative transfer, thus contributing to the construction of a required hierarchy of three-dimensional theoretical models. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Heng K.,ETH Zurich | Heng K.,Institute for Advanced Study | Menou K.,Columbia University | Menou K.,Perimeter Institute for Theoretical Physics | Phillipps P.J.,Geophysical Fluid Dynamics Laboratory
Monthly Notices of the Royal Astronomical Society | Year: 2011

The rapid pace of extrasolar planet discovery and characterization is legitimizing the study of their atmospheres via three-dimensional numerical simulations. The complexity of atmospheric modelling and its inherent non-linearity, together with the limited amount of data available, motivate model intercomparisons and benchmark tests. In the geophysical community, the Held-Suarez test is a standard benchmark for comparing dynamical core simulations of the Earth's atmosphere with different solvers, based on statistically averaged flow quantities. In the present study, we perform analogues of the Held-Suarez test for tidally locked exoplanets with the Geophysical Fluid Dynamics Laboratory (GFDL) Princeton Flexible Modelling System (fms) by subjecting both the spectral and finite difference dynamical cores to a suite of tests, including the standard benchmark for the Earth, a hypothetical tidally locked Earth, a 'shallow' hot Jupiter model and a 'deep' model of HD 209458b. We find qualitative and quantitative agreement between the solvers for the Earth, tidally locked Earth and shallow hot Jupiter benchmarks, but the agreement is less than satisfactory for the deep model of HD 209458b. Further investigation reveals that closer agreement may be attained by arbitrarily adjusting the values of the horizontal dissipation parameters in the two solvers, but it remains the case that the magnitude of the horizontal dissipation is not easily specified from first principles. Irrespective of radiative transfer or chemical composition considerations, our study points to limitations in our ability to accurately model hot Jupiter atmospheres with meteorological solvers at the level of 10 per cent for the temperature field and several tens of per cent for the velocity field. Direct wind measurements should thus be particularly constraining for the models. Our suite of benchmark tests also provides a reference point for researchers wishing to adapt their codes to study the atmospheric circulation regimes of tidally locked Earths/Neptunes/Jupiters. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

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