scholarly journals Insights into the early Eocene hydrological cycle from an ensemble of atmosphere–ocean GCM simulations

2015 ◽  
Vol 11 (4) ◽  
pp. 3277-3339 ◽  
Author(s):  
M. J. Carmichael ◽  
D. J. Lunt ◽  
M. Huber ◽  
M. Heinemann ◽  
J. Kiehl ◽  
...  
Keyword(s):  
General Circulation ◽  
Hydrological Cycle ◽  
Middle Eocene ◽  
Circulation Model ◽  
Large Error ◽  
Early Eocene ◽  
Air Temperatures ◽  
Simulated Precipitation ◽  
Precipitation Estimates ◽  
Simulated Surface

Abstract. Recent studies, utilising a range of proxies, indicate that a significant perturbation to global hydrology occurred at the Paleocene–Eocene Thermal Maximum (PETM; ~56 Ma). An enhanced hydrological cycle for the warm early Eocene is also suggested to have played a key role in maintaining high-latitude warmth during this interval. However, comparisons of proxy data to General Circulation Model (GCM) simulated hydrology are limited and inter-model variability remains poorly characterised, despite significant differences in simulated surface temperatures. In this work, we undertake an intercomparison of GCM-derived precipitation and P-E distributions within the EoMIP ensemble (Lunt et al., 2012), which includes previously-published early Eocene simulations performed using five GCMs differing in boundary conditions, model structure and precipitation relevant parameterisation schemes. We show that an intensified hydrological cycle, manifested in enhanced global precipitation and evaporation rates, is simulated for all Eocene simulations relative to preindustrial. This is primarily due to elevated atmospheric paleo-CO2, although the effects of differences in paleogeography/ice sheets are also of importance in some models. For a given CO2 level, globally-averaged precipitation rates vary widely between models, largely arising from different simulated surface air temperatures. Models with a similar global sensitivity of precipitation rate to temperature (dP/dT) display different regional precipitation responses for a given temperature change. Regions that are particularly sensitive to model choice include the South Pacific, tropical Africa and the Peri-Tethys, which may represent targets for future proxy acquisition. A comparison of early and middle Eocene leaf-fossil-derived precipitation estimates with the GCM output illustrates that a number of GCMs underestimate precipitation rates at high latitudes. Models which warm these regions, either via elevated CO2 or by varying poorly constrained model parameter values, are most successful in simulating a match with geologic data. Further data from low-latitude regions and better constraints on early Eocene CO2 are now required to discriminate between these model simulations given the large error bars on paleoprecipitation estimates. Given the clear differences apparent between simulated precipitation distributions within the ensemble, our results suggest that paleohydrological data offer an independent means by which to evaluate model skill for warm climates.

scholarly journals A model–model and data–model comparison for the early Eocene hydrological cycle

2016 ◽  
Vol 12 (2) ◽  
pp. 455-481 ◽  
Author(s):  
Matthew J. Carmichael ◽  
Daniel J. Lunt ◽  
Matthew Huber ◽  
Malte Heinemann ◽  
Jeffrey Kiehl ◽  
...  
Keyword(s):  
General Circulation ◽  
Model Comparison ◽  
Elevated Temperatures ◽  
Hydrological Cycle ◽  
Middle Eocene ◽  
Circulation Model ◽  
Large Error ◽  
Early Eocene ◽  
Air Temperatures ◽  
Simulated Precipitation

Abstract. A range of proxy observations have recently provided constraints on how Earth's hydrological cycle responded to early Eocene climatic changes. However, comparisons of proxy data to general circulation model (GCM) simulated hydrology are limited and inter-model variability remains poorly characterised. In this work, we undertake an intercomparison of GCM-derived precipitation and P − E distributions within the extended EoMIP ensemble (Eocene Modelling Intercomparison Project; Lunt et al., 2012), which includes previously published early Eocene simulations performed using five GCMs differing in boundary conditions, model structure, and precipitation-relevant parameterisation schemes. We show that an intensified hydrological cycle, manifested in enhanced global precipitation and evaporation rates, is simulated for all Eocene simulations relative to the preindustrial conditions. This is primarily due to elevated atmospheric paleo-CO2, resulting in elevated temperatures, although the effects of differences in paleogeography and ice sheets are also important in some models. For a given CO2 level, globally averaged precipitation rates vary widely between models, largely arising from different simulated surface air temperatures. Models with a similar global sensitivity of precipitation rate to temperature (dP∕dT) display different regional precipitation responses for a given temperature change. Regions that are particularly sensitive to model choice include the South Pacific, tropical Africa, and the Peri-Tethys, which may represent targets for future proxy acquisition. A comparison of early and middle Eocene leaf-fossil-derived precipitation estimates with the GCM output illustrates that GCMs generally underestimate precipitation rates at high latitudes, although a possible seasonal bias of the proxies cannot be excluded. Models which warm these regions, either via elevated CO2 or by varying poorly constrained model parameter values, are most successful in simulating a match with geologic data. Further data from low-latitude regions and better constraints on early Eocene CO2 are now required to discriminate between these model simulations given the large error bars on paleoprecipitation estimates. Given the clear differences between simulated precipitation distributions within the ensemble, our results suggest that paleohydrological data offer an independent means by which to evaluate model skill for warm climates.

scholarly journals Impact of model resolution on Holocene climate simulations of the Northern Hemisphere

2018 ◽  
Author(s):  
Axel Wagner ◽  
Gerrit Lohmann ◽  
Matthias Prange
Keyword(s):  
High Resolution ◽  
Radiative Forcing ◽  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Boreal Winter ◽  
Temperature Anomalies ◽  
Air Temperatures ◽  
Geographical Regions ◽  
Simulated Surface

Abstract. This study demonstrates the dependence of simulated surface air temperatures on variations in grid resolution and resolution-dependent orography in simulations of the Mid-Holocene. A set of Mid-Holocene sensitivity experiments is carried out with the atmospheric general circulation model ECHAM5 forced with sea surface temperature and sea ice fields from coupled simulations. Each experiment was performed in two resolution modes: low (~ 3.75°, 19 vertical levels) and high (~ 1.1°, 31 vertical levels). Results are compared to respective preindustrial runs. It is found that the large-scale temperature anomalies for the Mid-Holocene (compared to the preindustrial) are significantly different in the low- and high-resolution versions. For boreal winter, differences are related to circulation changes caused by the response to thermal forcing in conjunction with orographic resolution. For summer, shortwave cloud radiative forcing emerges as the predominant factor. In summary, the simulated Mid-Holocene temperature differences (low versus high resolution) reveal a response that regionally exceeds the Mid-Holocene to preindustrial modelled temperature anomalies, and show partly reversed signs across the same geographical regions. Our results imply that climate change simulations sensitively depend on the chosen grid resolutions.

scholarly journals Simulation of the isotopic composition of stratospheric water vapour – Part 1: Description and evaluation of the EMAC model

2015 ◽  
Vol 15 (10) ◽  
pp. 5537-5555 ◽  
Author(s):  
R. Eichinger ◽  
P. Jöckel ◽  
S. Brinkop ◽  
M. Werner ◽  
S. Lossow
Keyword(s):  
Isotopic Composition ◽  
Water Vapour ◽  
General Circulation ◽  
Climate Model ◽  
Hydrological Cycle ◽  
Circulation Model ◽  
Isotope Ratios ◽  
Physical Fractionation ◽  
Water Isotopologues ◽  
Stratospheric Water Vapour

Abstract. This modelling study aims at an improved understanding of the processes that determine the water vapour budget in the stratosphere by means of the investigation of water isotope ratios. An additional (and separate from the actual) hydrological cycle has been introduced into the chemistry–climate model EMAC, including the water isotopologues HDO and H218O and their physical fractionation processes. Additionally an explicit computation of the contribution of methane oxidation to H2O and HDO has been incorporated. The model expansions allow detailed analyses of water vapour and its isotope ratio with respect to deuterium throughout the stratosphere and in the transition region to the troposphere. In order to assure the correct representation of the water isotopologues in the model's hydrological cycle, the expanded system has been evaluated in several steps. The physical fractionation effects have been evaluated by comparison of the simulated isotopic composition of precipitation with measurements from a ground-based network (GNIP) and with the results from the isotopologue-enabled general circulation model ECHAM5-wiso. The model's representation of the chemical HDO precursor CH3D in the stratosphere has been confirmed by a comparison with chemical transport models (1-D, CHEM2D) and measurements from radiosonde flights. Finally, the simulated stratospheric HDO and the isotopic composition of water vapour have been evaluated, with respect to retrievals from three different satellite instruments (MIPAS, ACE-FTS, SMR). Discrepancies in stratospheric water vapour isotope ratios between two of the three satellite retrievals can now partly be explained.

scholarly journals Vegetation–climate feedbacks modulate rainfall patterns in Africa under future climate change

2016 ◽  
Vol 7 (3) ◽  
pp. 627-647 ◽  
Author(s):  
Minchao Wu ◽  
Guy Schurgers ◽  
Markku Rummukainen ◽  
Benjamin Smith ◽  
Patrick Samuelsson ◽  
...  
Keyword(s):  
Surface Energy ◽  
General Circulation ◽  
Hydrological Cycle ◽  
Regional Climate ◽  
Circulation Model ◽  
Future Climate ◽  
Tree Cover ◽  
Future Climate Change ◽  
Climate Projections ◽  
Area Index

Abstract. Africa has been undergoing significant changes in climate and vegetation in recent decades, and continued changes may be expected over this century. Vegetation cover and composition impose important influences on the regional climate in Africa. Climate-driven changes in vegetation structure and the distribution of forests versus savannah and grassland may feed back to climate via shifts in the surface energy balance, hydrological cycle and resultant effects on surface pressure and larger-scale atmospheric circulation. We used a regional Earth system model incorporating interactive vegetation–atmosphere coupling to investigate the potential role of vegetation-mediated biophysical feedbacks on climate dynamics in Africa in an RCP8.5-based future climate scenario. The model was applied at high resolution (0.44 × 0.44°) for the CORDEX-Africa domain with boundary conditions from the CanESM2 general circulation model. We found that increased tree cover and leaf-area index (LAI) associated with a CO2 and climate-driven increase in net primary productivity, particularly over subtropical savannah areas, not only imposed important local effect on the regional climate by altering surface energy fluxes but also resulted in remote effects over central Africa by modulating the land–ocean temperature contrast, Atlantic Walker circulation and moisture inflow feeding the central African tropical rainforest region with precipitation. The vegetation-mediated feedbacks were in general negative with respect to temperature, dampening the warming trend simulated in the absence of feedbacks, and positive with respect to precipitation, enhancing rainfall reduction over the rainforest areas. Our results highlight the importance of accounting for vegetation–atmosphere interactions in climate projections for tropical and subtropical Africa.

scholarly journals Climatic stability of the geographic origin of Antarctic precipitation simulated by an atmospheric general circulation model

1999 ◽  
Vol 29 ◽  
pp. 45-48 ◽  
Author(s):  
Gilles Delaygue ◽  
Valérie Masson ◽  
Jean Jouzel
Keyword(s):  
General Circulation Model ◽  
General Circulation ◽  
Latitudinal Gradient ◽  
Atmospheric General Circulation Model ◽  
Hydrological Cycle ◽  
Geographic Origin ◽  
Circulation Model ◽  
Sea Surface ◽  
Atmospheric General Circulation ◽  
Antarctic Precipitation

AbstractThe geographic origin of Antarctic precipitation is important for ice-core isotopic interpretation as well as ice-sheet mass-balance calculations. Here we estimate these moisture origins with the NASA/Goddard Institute of Space Studies atmospheric general circulation model, under different climatic conditions. This model reasonably simulates the broad features of the present-day observed hydrological cycle, and indicates a subtropical to subglacial (30-60° S) latitudinal origin for the Antarctic precipitation. We use different climatic reconstructions, all based on CLIMAP, for the Last Glacial Maximum (about 21000 years ago), which differ by the latitudinal sea-surface temperature gradient and seasonality. CLIMAP conditions increase the latitudinal gradient and the sea-ice extent, with the consequence of slightly enhancing the low-latitude origins. Shifting the seasonal cycle of oceanic prescribed conditions has an important effect on the hydrological cycle but less on the precipitation origin. Prescribing cooler tropical sea-surface temperatures, which decreases the latitudinal gradient, makes the latitudinal contributions closer to modern ones and increases the dominant oceanic sources. Globally the origins of Antarctic precipitation do not change significantly, either annually or seasonally.

scholarly journals Background albedo dynamics improve simulated precipitation variability in the Sahel region

2013 ◽  
Vol 4 (2) ◽  
pp. 595-626
Author(s):  
F. S. E. Vamborg ◽  
V. Brovkin ◽  
M. Claussen
Keyword(s):  
Land Surface ◽  
General Circulation ◽  
Surface Albedo ◽  
Rainfall Variability ◽  
Circulation Model ◽  
Dynamic Background ◽  
Simulated Precipitation ◽  
Sst Forcing ◽  
Rainfall Anomalies ◽  
Sahel Region

Abstract. Using the general circulation model ECHAM5-JSBACH forced by observed sea surface temperatures (SSTs) for the 20th century, we investigate the role of vegetation and land surface albedo dynamics in shaping rainfall variability in the Sahel. We use two different land surface albedo schemes, one in which the albedo of the canopy is varying and one in which additionally the albedo changes of the surface below the canopy are taken into account. The SST-forcing provides the background for simulating the observed decadal signal in Sahelian rainfall, though the respone to SST-forcing only is not strong enough to fully capture the observed signal. The introduction of dynamic vegetation leads to an increase in inter-annual variability of the rainfall, and gives rise to an increased number of high amplitude rainfall anomaly events. The dynamic background albedo leads to an increased persistence of the rainfall anomalies. The increase in persistence means that the difference between the dry and the wet decades is increased compared to the other simulations, and thus more closely matching the observed absolute change between these two periods. These results highlight the need for a consistent representation of land surface albedo dynamics for capturing the full extent of rainfall anomalies in the Sahel.

scholarly journals Impacto da duplicação de CO2 no clima global simulado por um modelo de circulação geral da atmosfera

2004 ◽  
Vol 27 ◽  
pp. 27-52
Author(s):  
Felipe Das Neves Roque da Silva ◽  
José Ricardo Almeida França
Keyword(s):  
General Circulation ◽  
Climate Changes ◽  
Hydrological Cycle ◽  
Circulation Model ◽  
Co2 Concentration ◽  
Polar Regions ◽  
Control Case ◽  
Model Resolution ◽  
Low Latitudes ◽  
Atmosphere General Circulation Model

The objective of this work is to evaluate climate changes caused by atmospheric CO2 concentration duplication. The LMD-Z atmosphere general circulation model (AGCM) was used (Laboratoire de Météorologie Dynamique - France). The model was integrated for a fifty years period and only the last forty years were used for analyses. This experiment have made two simulations: the first using the current CO2 concentration (control case) and the second using this concentration doubled (duplication case). Both were made with a variable spatial resolution with maximum of it centered in Rio de Janeiro. This way, there is a significant increase of model resolution in this region. To verify climate changes, anomaly fields generated by the model (duplication case minus control) were studied. It was possible to observe some characteristic effects of this type of experiment, such as great temperature increasing at surface in polar regions and in upper levels at low latitudes, cooling in stratosphere and intensification of hydrological cycle.

scholarly journals Simulation of the isotopic composition of stratospheric water vapour – Part 1: Description and evaluation of the EMAC model

2014 ◽  
Vol 14 (17) ◽  
pp. 23807-23846 ◽  
Author(s):  
R. Eichinger ◽  
P. Jöckel ◽  
S. Brinkop ◽  
M. Werner ◽  
S. Lossow
Keyword(s):  
Isotopic Composition ◽  
Water Vapour ◽  
General Circulation ◽  
Climate Model ◽  
Hydrological Cycle ◽  
Circulation Model ◽  
Isotope Ratios ◽  
Physical Fractionation ◽  
Water Isotopologues ◽  
Stratospheric Water Vapour

Abstract. This modelling study aims on an improved understanding of the processes, that determine the water vapour budget in the stratosphere by means of the investigation of water isotope ratios. At first, a separate hydrological cycle has been introduced into the chemistry-climate model EMAC, including the water isotopologues HDO and H218O and their physical fractionation processes. Additionally an explicit computation of the contribution of methane oxidation to HDO has been incorporated. The model expansions allow detailed analyses of water vapour and its isotope ratio with respect to deuterium throughout the stratosphere and in the transition region to the troposphere. In order to assure the correct representation of the water isotopologues in the model's hydrological cycle, the expanded system has been evaluated in several steps. The physical fractionation effects have been evaluated by comparison of the simulated isotopic composition of precipitation with measurements from a ground-based network (GNIP) and with the results from the isotopologue-enabled general circulation model ECHAM5-wiso. The model's representation of the chemical HDO precursor CH3D in the stratosphere has been confirmed by a comparison with chemical transport models (CHEM1D, CHEM2D) and measurements from radiosonde flights. Finally, the simulated stratospheric HDO and the isotopic composition of water vapour have been evaluated, with respect to retrievals from three different satellite instruments (MIPAS, ACE-FTS, SMR). Discrepancies in stratospheric water vapour isotope ratios between two of the three satellite retrievals can now partly be explained.

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