CO2 climate sensitivity and snow-sea-ice albedo parameterization in an atmospheric GCM coupled to a mixed-layer ocean model   总被引：1，自引：0，他引：1  

Gerald A. Meehl  Warren M. Washington 《Climatic change》1990,16(3):283-306

The snow-sea-ice albedo parameterization in an atmospheric general circulation model (GCM), coupled to a simple mixed-layer ocean and run with an annual cycle of solar forcing, is altered from a version of the same model described by Washington and Meehl (1984). The model with the revised formulation is run to equilibrium for 1 × CO₂ and 2 × CO₂ experiments. The 1 ×CO₂ (control) simulation produces a global mean climate about 1° warmer than the original version, and sea-ice extent is reduced. The model with the altered parameterization displays heightened sensitivity in the global means, but the geographical patterns of climate change due to increased carbon dioxide (CO₂) are qualitatively similar. The magnitude of the climate change is affected, not only in areas directly influenced by snow and ice changes but also in other regions of the globe, including the tropics where sea-surface temperature, evaporation, and precipitation over the oceans are greater. With the less-sensitive formulation, the global mean surface air temperature increase is 3.5 °C, and the increase of global mean precipitation is 7.12%. The revised formulation produces a globally averaged surface air temperature increase of 4.04 °C and a precipitation increase of 7.25%, as well as greater warming of the upper tropical troposphere. Sensitivity of surface hydrology is qualitatively similar between the two cases with the larger-magnitude changes in the revised snow and ice-albedo scheme experiment. Variability of surface air temperature in the model is comparable to observations in most areas except at high latitudes during winter. In those regions, temporal variation of the sea-ice margin and fluctuations of snow cover dependent on the snow-ice-albedo formulation contribute to larger-than-observed temperature variability. This study highlights an uncertainty associated with results from current climate GCMs that use highly parameterized snow-sea-ice albedo schemes with simple mixed-layer ocean models.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

Low-frequency variability and CO2 transient climate change. Part 3. Intermonthly and interannual variability     

Gerald A Meehl  Matthew Wheeler  Warren M Washington 《Climate Dynamics》1994,10(6-7):277-303

Components of interannual, intermonthly, and total monthly variability of lower troposphere temperature are calculated from a global coupled ocean-atmosphere general circulation model (GCM) (referred to as the coupled model), from the same atmospheric model coupled to a nondynamic mixedlayer ocean (referred to as the mixed-layer model), and from microwave sounding unit (MSU) satellite data. The coupled model produces most features of intermonthly and interannual variability compared to the MSU data, but with somewhat reduced amplitude in the extratropics and increased variability in the tropical western Pacific and tropical Atlantic. The relatively short 14-year period of record of the MSU data precludes definitive conclusions about variability in the observed system at longer time scales (e.g., decadal or longer). Different 14-year periods from the coupled model show variability on those longer time scales that were noted in Part 1 of this series. The relative contributions of intermonthly and interannual variability that make up the total monthly variability are similar between the coupled model and the MSU data, suggesting that similar mechanisms are at work in both the model and observed system. These include El Niño-Southern Oscillation (ENSO)-type interannual variability in the tropics, Madden-Julian Oscillation (MJO) type intermonthly variability in the tropics, and blocking-type intermonthly variability in the extratropics. Manifestations of all of these features have been noted in various versions of the model. Significant changes of variability noted in the coupled model with doubled carbon dioxide differ from those in our mixed-layer model and earlier studies with mixed-layer models. In particular, in our mixed-layer model intermonthly and interannual variability changes are similar with a mixture of regional increases and decreases, but with mainly decreases in the zonal mean from about 20°S to 60°N and near 60°S. In the coupled model, intermonthly and interannual changes of variability with doubled CO₂ show mostly increases of tropical interannual variability and decreases of intermonthly variability near 60°N. These changes in the tropics are related to changes in ENSO, the south Asian monsoon, and other regional hydrological regimes, while the alterations near 60°N are likely associated with changes in blocking activity. These results point to the important contribution from ENSO seen in the coupled model and the MSU data that are not present in the mixed-layer model.  相似文献   

Ice-albedo feedback in a CO2-doubling simulation     

Robert E. Dickinson  Gerald A. Meehl  Warren M. Washington 《Climatic change》1987,10(3):241-248

We estimate the feedback of sea-ice change to the warming from CO₂-doubling according to the simulation of Washington and Meehl (1984). Without ice-snow albedo feedback, their global warming of 3.5 °C would have been 2.2. °C according to our estimate of the ice-snow feedback. About 80% of the albedo change from ice and snow occurred in the Southern Hemisphere. Whether this change was an overestimate will require further study.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

Climate sensitivity due to increased CO2: experiments with a coupled atmosphere and ocean general circulation model     

Warren M Washington  Gerald A Meehl 《Climate Dynamics》1989,4(1):1-38

A version of the National Center for Atmospheric Research community climate model — a global, spectral (R15) general circulation model — is coupled to a coarse-grid (5° latitude-] longitude, four-layer) ocean general circulation model to study the response of the climate system to increases of atmospheric carbon dioxide (CO₂). Three simulations are run: one with an instantaneous doubling of atmospheric CO₂ (from 330 to 660 ppm), another with the CO₂ concentration starting at 330 ppm and increasing linearly at a rate of 1% per year, and a third with CO₂ held constant at 330 pm. Results at the end of 30 years of simulation indicate a globally averaged surface air temperature increase of 1.6° C for the instantaneous doubling case and 0.7°C for the transient forcing case. Inherent characteristics of the coarse-grid ocean model flow sea-surface temperatures (SSTs) in the tropics and higher-than-observed SSTs and reduced sea-ice extent at higher latitudes] produce lower sensitivity in this model after 30 years than in earlier simulations with the same atmosphere coupled to a 50-m, slab-ocean mixed layer. Within the limitations of the simulated meridional overturning, the thermohaline circulation weakens in the coupled model with doubled CO₂ as the high-latitude ocean-surface layer warms and freshens and westerly wind stress is decreased. In the transient forcing case with slowly increasing CO₂ (30% increase after 30 years), the zonal mean warming of the ocean is most evident in the surface layer near 30°–50° S. Geographical plots of surface air temperature change in the transient case show patterns of regional climate anomalies that differ from those in the instantaneous CO₂ doubling case, particularly in the North Atlantic and northern European regions. This suggests that differences in CO₂ forcing in the climate system are important in CO₂ response in regard to time-dependent climate anomaly regimes. This confirms earlier studies with simple climate models that instantaneous CO₂ doubling simulations may not be analogous in all respects to simulations with slowly increasing CO₂.A portion of this study is supported by the US Department of Energy as part of its Carbon Dioxide Research Program  相似文献   

A measurement domain receiver autonomous integrity monitoring algorithm   总被引：2，自引：2，他引：2  

Shaojun Feng  Washington Y. Ochieng  David Walsh  Rigas Ioannides 《GPS Solutions》2006,10(2):85-96

One of the key approaches to monitor the integrity of Global Satellite Navigation Systems (GNSS) is receiver autonomous integrity monitoring (RAIM). Existing RAIM algorithms utilise two tests in the position domain (for RAIM availability) and measurement domain (for failure detection). This paper proposes an alternative RAIM algorithm, which is based entirely in the measurement domain. This algorithm can be used for sensitivity analyses to support performance specification and system design. It can also be used during actual flight operations where the trigger is the phase of flight and its required navigation performance (RNP) parameters. This is made possible by computationally efficient calculation of the chi-squared parameters. The algorithm reverts to the current approach if the phase of flight is unknown. Simulation results for non-precision approach (NPA) have been used to demonstrate the effectiveness of the proposed algorithm.  相似文献   

Carrier phase-based integrity monitoring for high-accuracy positioning   总被引：4，自引：3，他引：1  

Shaojun Feng  Washington Ochieng  Terry Moore  Chris Hill  Chris Hide 《GPS Solutions》2009,13(1):13-22

Pseudorange-based integrity monitoring, for example receiver autonomous integrity monitoring (RAIM), has been investigated for many years and is used in various applications such as non-precision approach phase of flight. However, for high-accuracy applications, carrier phase-based RAIM (CRAIM), an extension of pseudorange-based RAIM (PRAIM) must be used. Existing CRAIM algorithms are a direct extension of PRAIM in which the carrier phase ambiguities are estimated together with the estimation of the position solution. The main issues with the existing algorithms are reliability and robustness, which are dominated by the correctness of the ambiguity resolution, ambiguity validation and error sources such as multipath, cycle slips and noise correlation. This paper proposes a new carrier phase-based integrity monitoring algorithm for high-accuracy positioning, using a Kalman filter. The ambiguities are estimated together with other states in the Kalman filter. The double differenced pseudorange, widelane and carrier phase observations are used as measurements in the Kalman filter. This configuration makes the positioning solution both robust and reliable. The integrity monitoring is based on a number of test statistics and error propagation for the determination of the protection levels. The measurement noise and covariance matrices in the Kalman filter are used to account for the correlation due to differencing of measurements and in the construction of the test statistics. The coefficient used to project the test statistic to the position domain is derived and the synthesis of correlated noise errors is used to determine the protection level. Results from four cases based on limited real data injected with simulated cycle slips show that residual cycle slips have a negative impact on positioning accuracy and that the integrity monitoring algorithm proposed can be effective in detecting and isolating such occurrences if their effects violate the integrity requirements. The CRAIM algorithm proposed is suitable for use within Kalman filter-based integrated navigation systems.

Shaojun FengEmail:

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Erratum to: Economic risk assessment of Cotopaxi volcano,Ecuador, in case of a future lahar emplacement     

Rodriguez  Fabian  Toulkeridis  Theofilos  Sandoval  Washington  Padilla  Oswaldo  Mato  Fernando 《Natural Hazards》2017,85(1):619-620

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The Rondonian-San Ignacio Province in the SW Amazonian Craton: An overview     

Jorge Silva Bettencourt  Washington Barbosa Leite  Amarildo Salina Ruiz  Ramiro Matos  Bruno Leonelo Payolla  Richard M. Tosdal 《Journal of South American Earth Sciences》2010,29(1):28-46

The Rondonian-San Ignacio Province (1.56–1.30 Ga) is a composite orogen created through successive accretion of arcs, ocean basin closure and final oblique microcontinent–continent collision. The effects of the collision are well preserved mostly in the Paraguá Terrane (Bolivia and Mato Grosso regions) and in the Alto Guaporé Belt and the Rio Negro-Juruena Province (Rondônia region), considering that the province was affected by later collision-related deformation and metamorphism during the Sunsás Orogeny (1.25–1.00 Ga). The Rondonian-San Ignacio Province comprises: (1) the Jauru Terrane (1.78–1.42 Ga) that hosts Paleoproterozoic basement (1.78–1.72 Ga), and the Cachoeirinha (1.56–1.52 Ga) and the Santa Helena (1.48–1.42 Ga) accretionary orogens, both developed in an Andean-type magmatic arc; (2) the Paraguá Terrane (1.74–1.32 Ga) that hosts pre-San Ignacio units (>1640 Ma: Chiquitania Gneiss Complex, San Ignacio Schist Group and Lomas Manechis Granulitic Complex) and the Pensamiento Granitoid Complex (1.37–1.34 Ga) developed in an Andean-type magmatic arc; (3) the Rio Alegre Terrane (1.51–1.38 Ga) that includes units generated in a mid-ocean ridge and an intra-oceanic magmatic arc environments; and (4) the Alto Guaporé Belt (<1.42–1.34 Ga) that hosts units developed in passive marginal basin and intra-oceanic arc settings. The collisional stage (1.34–1.32 Ga) is characterized by deformation, high-grade metamorphism, and partial melting during the metamorphic peak, which affected primarily the Chiquitania Gneiss Complex and Lomas Manechis Granulitic Complex in the Paraguá Terrane, and the Colorado Complex and the Nova Mamoré Metamorphic Suite in the Alto Guaporé Belt. The Paraguá Block is here considered as a crustal fragment probably displaced from its Rio Negro-Juruena crustal counterpart between 1.50 and 1.40 Ga. This period is characterized by extensive A-type and intra-plate granite magmatism represented by the Rio Crespo Intrusive Suite (ca. 1.50 Ga), Santo Antonio Intrusive Suite (1.40–1.36 Ga), and the Teotônio Intrusive Suite (1.38 Ga). Magmatism of these types also occur at the end of the Rondonian-San Ignacio Orogeny, and are represented by the Alto Candeias Intrusive Suite (1.34–1.36 Ga), and the São Lourenço-Caripunas Intrusive Suite (1.31–1.30 Ga). The cratonization of the province occurred between 1.30 and 1.25 Ga.  相似文献   

Groundwater N speciation and redox control of organic N mineralization by O₂ reduction to H₂O₂     

John W. Washington  Robert C. Thomas  Katherine L. Schroer 《Geochimica et cosmochimica acta》2006,70(14):3533-3548

Excess N from agriculture induces eutrophication in major river systems and hypoxia in coastal waters throughout the world. Much of this N is from headwaters far up the watersheds. In turn, much of the N in these headwaters is from ground-water discharge. Consequently, the concentrations and forms of N in groundwater are important factors affecting major aquatic ecosystems; despite this, few data exist for several species of N in groundwater and controls on speciation are ill-defined. Herein, we report N speciation for a spring and well that were selected to reflect agricultural impacts, and a spring and well that show little to no agricultural-N impact. Samples were characterized for NO₃⁻, NO₂⁻, N₂O, NH₄⁺, urea, particulate organic N(), and dissolved organic N(). These analytes were monitored in the agricultural spring for up to two years along with other analytes that we reported upon previously. For all samples, when oxidized N was present, the dominant species was NO₃⁻ (88-98% of total fixed N pool) followed by (<4-12%) and only trace fractions of the other N analytes. In the non-agriculturally impacted well sample, which had no quantifiable NO₃⁻ or dissolved O₂, comprised the dominant fraction (68%) followed by NH₄⁺ (32%), with only a trace balance comprised of other N analytes. Water drawn from the well, spring and a wetland situated in the agricultural watershed also were analyzed for dissolved N₂ and found to have a fugacity in excess of that of the atmosphere. H₂O₂ was analyzed in the agricultural spring to evaluate the O₂/H₂O₂ redox potential and compare it to other calculated potentials. The potential of the O₂/H₂O₂ couple was close in value to the NO₃⁻/NO₂⁻ couple suggesting the important role of H₂O₂ as an O₂-reduction intermediate product and that O₂ and NO₃⁻ are reduced concomitantly. The O₂/H₂O₂ and NO₃⁻/NO₂⁻ couples also were close in value to a cluster of other inorganic N and Fe couples indicating near partial equilibrium among these species. Urea mineralization to NO₂⁻ was found to approach equilibrium with the reduction of O₂ to H₂O₂. By modeling as amide functional groups, as justified by recent analytical work, similar thermodynamic calculations support that mineralization to NO₂⁻ proceeds nearly to equilibrium with the reduction of O₂ to H₂O₂ as well. This near equilibration of redox couples for urea- and -oxidation with O₂-reduction places these two couples within the oxidized redox cluster that is shared among several other couples we have reported previously. In the monitored agricultural spring, [NO₃⁻] was lower in the summer than at other times, whereas [N₂O] was higher in the summer than at other times, perhaps reflecting a seasonal variation in the degree of denitrification reaction progress. No other N analytes were observed to vary seasonally in our study. In the well having no agricultural-N impact, C_org/N_org = 5.5, close to the typical value for natural aqueous systems of about 6.6. In the agricultural watershed C_org/N_org varied widely, from ∼1.2 to ?9.  相似文献   

Monte Carlo simulations of radio pulses in atmospheric showers using ZHAireS     

Jaime Alvarez-Muñiz  Washington R. Carvalho Jr.Enrique Zas 《Astroparticle Physics》2012,35(6):325-341

We present predictions for the radio pulses emitted by extensive air showers using ZHAireS, an AIRES-based Monte Carlo code that takes into account the full complexity of ultra-high energy cosmic-ray induced shower development in the atmosphere, and allows the calculation of the electric field in both the time and frequency domains. We do not presuppose any emission mechanism and our results are compatible with a superposition of geomagnetic and charge excess radio emission effects. We investigate the polarization of the electric field as well as the effects of the refractive index n and shower geometry on the radio pulses. We show that geometry, coupled to the relativistic effects that appear when using a realistic refractive index n > 1, play a prominent role on the radio emission of air showers.  相似文献