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States of maximum entropy production in a one-dimensional vertical model with convective adjustment 总被引:2,自引:0,他引:2
We investigate the hypothesis that the atmosphere is constrained to maximize its entropy production by using a one-dimensional (1-D) vertical model. We prescribe the lapse rate in the convective layer as that of the standard troposphere. The assumption that convection sustains a critical lapse rate was absent in previous studies, which focused on the vertical distribution of climatic variables, since such a convective adjustment reduces the degrees of freedom of the system and may prevent the application of the maximum entropy production (MEP) principle. This is not the case in the radiative-convective model (RCM) developed here, since we accept a discontinuity of temperatures at the surface similar to that adopted in many RCMs.
For current conditions, the MEP state gives a difference between the ground temperature and the air temperature at the surface ≈10 K. In comparison, conventional RCMs obtain a discontinuity ≈2K only. However, the surface boundary layer velocity in the MEP state appears reasonable (≈m s−1 ). Moreover, although the convective flux at the surface in MEP states is almost uniform in optically thick atmospheres, it reaches a maximum value for an optical thickness similar to current conditions. This additional result may support the maximum convection hypothesis suggested by Paltridge (1978 ). 相似文献
For current conditions, the MEP state gives a difference between the ground temperature and the air temperature at the surface ≈10 K. In comparison, conventional RCMs obtain a discontinuity ≈2K only. However, the surface boundary layer velocity in the MEP state appears reasonable (≈m s
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KEVIN ROBERT GURNEY RACHEL M. LAW A. SCOTT DENNING PETER J. RAYNER DAVID BAKER PHILIPPE BOUSQUET LORI BRUHWILER YU-HAN CHEN PHILIPPE CIAIS SONGMIAO FAN INEZ Y. FUNG MANUEL GLOOR MARTIN HEIMANN KAZ HIGUCHI JASMIN JOHN EVA KOWALCZYK TAKASHI MAKI SHAMIL MAKSYUTOV PHILIPPE PEYLIN MICHAEL PRATHER BERNARD C. PAK JORGE SARMIENTO SHOICHI TAGUCHI TARO TAKAHASHI CHIU-WAI YUEN 《Tellus. Series B, Chemical and physical meteorology》2003,55(2):555-579
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KEVIN TIMONEY GEORGE PETERSON PAT FARGEY MURRAY PETERSON STEVE McCANNY ROSS WEIN 《Climatic change》1997,35(4):463-483
A historic record of spring ice-jam floods of the Peace-Athabasca Delta was analyzed for the years 1826–1995. The temporal pattern of flooding is non-random. The likelihood of a flood following a flood, or a non-flood following a non-flood, is greater than expected by chance. Probability analysis of flood occurrence reveals that the period 1860–1880 was a time of unusually few floods, and the period 1915–1950 was a time of unusually frequent floods. The long-term flood frequency is 1 flood in 6.25 years. Changes in flood frequency over the record reveal a pattern of oscillation described by a sine-based model that is correlated with the long-term (Gleissberg) cycle of solar activity. Monte Carlo simulation was used to test a Bennett Dam Model and a Cyclic Model. The Bennett Dam Model is unlikely to have generated the observed flood history (p=0.04). The observed flood history shows a better fit to the Cyclic Model (p=0.65). No correlations between floods and ENSO cold or warm events was detected. The most recent wet period began about 1900 and ended in the early 1960's prior to completion of the W. A. C. Bennett Dam in British Columbia. As independent corroboration of climatically-driven changes in flood frequency we present three additional lines of evidence. The pattern of annual muskrat returns (95 year record) reveals both 10 year cycles and long-term patterns that agree well with the observed flood cycle. The annual area burned in Wood Buffalo National Park is inversely related to flood occurrence. Incised channels and dendritic drainage patterns in the bed of Lake Mamawi provide probable evidence of a previous dry period in the delta. Climatic change or oscillation likely underlies the drying trend observed in recent decades in the Peace-Athabasca Delta. 相似文献
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By C. AULAGNIER P. RAYNER P. CIAIS R. VAUTARD L. RIVIER M. RAMONET 《Tellus. Series B, Chemical and physical meteorology》2010,62(1):14-25
In this issue, Ramonet et al. revealed a positive trend in European, atmospheric CO2 concentrations relative to a marine, North Atlantic reference baseline, for the years 2001–2006. The observed build up mainly occurred during the cold season where it reaches a 0.8 ppm yr−1 at low-altitude stations to a 0.3 ppm yr−1 at mid-altitude stations. We explore the cause of this build-up using the mesoscale model CHIMERE. We first model the observed trends, using interannually varying fluxes and transport, then suppress the interannual variability in fluxes or aspects of transport to elucidate the cause. The run with no interannual variability in fluxes still matches observed trends suggesting that transport is the major cause. Separate runs varying either boundary layer height or winds show that changes in boundary layer height explain the trends at low-altitude stations within the continents while changes in wind regimes drive changes elsewhere. 相似文献
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By NATCHAYA PINGINTHA MONIQUE Y. LECLERC JOHN P. BEASLEY Jr. GENGSHENG ZHANG CHUCKREE SENTHONG 《Tellus. Series B, Chemical and physical meteorology》2010,62(1):47-58
This paper uses a refined soil gradient method to estimate soil CO2 efflux. Six different models are used to determine the relative gas diffusion coefficient (ξ). A weighted harmonic averaging is used to estimate the soil CO2 diffusion coefficient, yielding a better estimate of soil CO2 efflux. The resulting soil CO2 efflux results are then compared to the soil CO2 efflux measured with a soil chamber. Depending on the choice of ξ model used, the estimated soil CO2 efflux using the gradient method reasonably approximates the efflux obtained using the soil chamber method. In addition, the estimated soil CO2 efflux obtained by this improved method is well described by an exponential function of soil temperature at a depth of 0.05 m with the temperature sensitivity ( Q 10 ) of 1.81 and a linear function of soil moisture at a depth of 0.12 m, in general agreement with previous findings. These results suggest that the gradient method is a practical cost-effective means to measure soil CO2 emissions. Results from the present study suggest that the gradient method can be used successfully to measure soil CO2 efflux provided that proper attention is paid to the judicious use of the proper diffusion coefficient. 相似文献
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Sea surface temperature (SST) anomalies associated with El Niño/Southern Oscillation (ENSO) constitute a major source of predictability in the tropics. We evaluate the ability of a regional climate model (the Rossby Centre Atmospheric Model; RCA) to downscale SST and large-scale atmospheric anomalies associated with ENSO. RCA is configured over the tropical east Pacific and tropical Americas and runs for the period 1979–2005, using European Centre for Medium-Range Weather Forecasts (ECMWF) lateral and surface boundary conditions. We study the ability of RCA to represent regional patterns of precipitation, with respect to both the climatology and interannual variability associated with ENSO. The latter is achieved by grouping the simulations into El Niño and La Niña composites and studying the delayed response of precipitation to SST forcing in four regions of Central and South America.
In this paper, we concentrate on seasonal mean timescales. We find that RCA accurately simulates the main features of the precipitation climatology over the four regions and also reproduces the majority of the documented regional responses to ENSO forcing. Furthermore, the model captures the variability in precipitation anomalies between different ENSO events. The model exhibits a wet bias over the northern Amazon and slightly overestimates the magnitude of ENSO anomalies over Central America. 相似文献
In this paper, we concentrate on seasonal mean timescales. We find that RCA accurately simulates the main features of the precipitation climatology over the four regions and also reproduces the majority of the documented regional responses to ENSO forcing. Furthermore, the model captures the variability in precipitation anomalies between different ENSO events. The model exhibits a wet bias over the northern Amazon and slightly overestimates the magnitude of ENSO anomalies over Central America. 相似文献
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Contrasting diagenesis of two Carboniferous Oolites from South Wales: a tale of climatic influence 总被引:2,自引:0,他引:2
Two oolites in the Dinantian (Mississippian/Lower Carboniferous) of Glamorgan, SW Britain, were deposited in similar depositional environments but have contrasting diagenetic histories. The Brofiscin and Gully Oolites occur in the upper parts of shallowing-upward sequences, formed through strandplain progradation and sand shoal and barrier growth upon a southward-dipping carbonate ramp. The Brofiscin Oolite is characterized by a first-generation cement of equant calcite spar, preferentially located at grain-contacts and forming non-isopachous fringes around grains, interpreted as meteoric vadose and phreatic in origin. Isopachous fibrous calcite fringes of marine origin are rather rare and occur only at a few horizons. Burial compaction was not important and porosity was occluded by poikilotopic calcite spar. Fitted grain-grain contacts locally occur and could be the result of near-surface vadose dissolution-compaction. Syntaxial overgrowths on echinoderm debris are common. Pre-compaction overgrowths are cloudy (inclusion-rich) and probably of meteoric origin, and post-compaction overgrowths are inclusion-free. By contrast, the Gully Oolite has little first-generation cement. However, marine fibrous calcite is common in oolitic intraclasts, as isopachous fringes of acicular calcite crystals closely associated with peloidal internal sediment; and early equant, drusy calcite spar occurs in the uppermost part of the Gully, beneath a prominent palaeokarst where pedogenic cements also occur. The major feature of Gully diagenesis is burial compaction, resulting in extensive grain-grain dissolution and microstylolitic grain contacts, and post-compaction poikilotopic spar occluded remaining porosity. The Brofiscin Oolite is pervasively dolomitized up-dip but the Gully Oolite for the most part only contains scattered pre-compaction dolomite rhombs and late veins of baroque dolomite, with less pervasive dolomitization. The difference in diagenetic style of the two Dinantian oolites is attributed to prevailing climate. The paucity of early meteoric cements in the Gully is a result of an arid climate, and this is supported by the nature of the capping palaeokarst. The abundant meteoric cements in the Brofiscin reflect a more humid climate, and effective meteoric recharge also resulted in up-dip pervasive mixing-zone dolomitization. The style of early diagenesis in these two oolites exerted a major control on the later burial diagenesis: in the Brofiscin, the early cements inhibited grain-grain dissolution and pressure solution, while these processes operated extensively in the Gully Oolite. Thus, prevailing climate can influence a limestone's diagenetic history from near-surface through into deep burial. 相似文献