The Experts below are selected from a list of 102 Experts worldwide ranked by ideXlab platform
U Cubasch - One of the best experts on this subject based on the ideXlab platform.
-
the north atlantic oscillation as an indicator for greenhouse gas induced regional climate change
Climate Dynamics, 1999Co-Authors: Heiko Paeth, Andreas Hense, Rita Glowienkahense, S Voss, U CubaschAbstract:The time-dependent variability of the North Atlantic Oscillation is examined in an observational data set and several model data sets with greenhouse-gas-induced external forcings. The index of the North Atlantic Oscillation state is derived from the time series of mean latitudinal position and central pressure of the Icelandic Low and the Azores High considering the synchronous meridional shifting of the two pressure systems. While the North Atlantic Oscillation is characterized by intensive interannual variability, the low-pass filtered index time series shows a decadal component with a time scale of about 50 y within almost 120 y of observation. Since the late 1960s we observe a positive trend and a transition to a strong positive phase of the phenomenon indicative of a pre-dominantly zonal circulation over the North Atlantic. This trend occurs equally in the observations and all examined model data sets with increasing greenhouse-gas-concentration and Atmosphere-Ocean Coupling. We find statistical evidence that the radiative forcing by increasing CO2 concentration has a significant influence on the simulated variability of the North Atlantic Oscillation on time scales of 60 y and longer, independent of the initial conditions and the model version. The seasonal response is strongest in late summer and winter. The interannual variability of the North Atlantic Oscillation states on time scales less than 10 y decreases synchronously with the positive trend of its decadal-mean state implying a stabilization of its present and future zonal state.
Heiko Paeth - One of the best experts on this subject based on the ideXlab platform.
-
the north atlantic oscillation as an indicator for greenhouse gas induced regional climate change
Climate Dynamics, 1999Co-Authors: Heiko Paeth, Andreas Hense, Rita Glowienkahense, S Voss, U CubaschAbstract:The time-dependent variability of the North Atlantic Oscillation is examined in an observational data set and several model data sets with greenhouse-gas-induced external forcings. The index of the North Atlantic Oscillation state is derived from the time series of mean latitudinal position and central pressure of the Icelandic Low and the Azores High considering the synchronous meridional shifting of the two pressure systems. While the North Atlantic Oscillation is characterized by intensive interannual variability, the low-pass filtered index time series shows a decadal component with a time scale of about 50 y within almost 120 y of observation. Since the late 1960s we observe a positive trend and a transition to a strong positive phase of the phenomenon indicative of a pre-dominantly zonal circulation over the North Atlantic. This trend occurs equally in the observations and all examined model data sets with increasing greenhouse-gas-concentration and Atmosphere-Ocean Coupling. We find statistical evidence that the radiative forcing by increasing CO2 concentration has a significant influence on the simulated variability of the North Atlantic Oscillation on time scales of 60 y and longer, independent of the initial conditions and the model version. The seasonal response is strongest in late summer and winter. The interannual variability of the North Atlantic Oscillation states on time scales less than 10 y decreases synchronously with the positive trend of its decadal-mean state implying a stabilization of its present and future zonal state.
Wojciech W Grabowski - One of the best experts on this subject based on the ideXlab platform.
-
impact of explicit atmosphere ocean Coupling on mjo like coherent structures in idealized aquaplanet simulations
Journal of the Atmospheric Sciences, 2006Co-Authors: Wojciech W GrabowskiAbstract:This paper discusses the impact of the atmosphere–ocean Coupling on the large-scale organization of tropical convection simulated by an idealized global model applying the Cloud-Resolving Convection Parameterization (CRCP; superparameterization). Because the organization resembles the Madden–Julian Oscillation (MJO), the results contribute to the debate concerning the role of atmosphere–ocean Coupling in tropical intraseasonal oscillations. The modeling setup is an aquaplanet with globally uniform mean sea surface temperature (SST) of 30°C (tropics everywhere) in radiative–convective quasi equilibrium. The simulations apply an interactive radiation transfer model and a slab ocean model with a fixed oceanic mixed layer depth. Results from several 80and 100-day-long simulations are discussed, where the only difference between the simulations is the prescribed oceanic mixed layer depth, which varied from 5 to 45 m. A simulation with a very deep oceanic mixed layer is also performed to represent constant-SST conditions. The simulations demonstrate that the interactive SST impedes the development of large-scale organization and has insignificant impact on the dynamics of mature MJO-like systems. The impediment is the result of a negative feedback between the large-scale organization of convection and SST, the convection–SST feedback. In this feedback, SST increases in regions of already suppressed convection and decreases in regions with enhanced convection, thus hindering the large-scale organization. Once developed, however, the MJO-like systems are equally strong in interactive and constant-SST simulations, and compare favorably with the observed MJO. The above impacts of the atmosphere–ocean Coupling contradict the majority of previous studies using traditional general circulation models, where, typically, an enhancement of the intraseasonal signal occurs compared to prescribed-SST simulations. An explanation of this discrepancy is suggested.
Remi Thieblemont - One of the best experts on this subject based on the ideXlab platform.
-
solar signals in cmip 5 simulations effects of atmosphere ocean Coupling
Quarterly Journal of the Royal Meteorological Society, 2016Co-Authors: Stergios Misios, Daniel M Mitchell, L J Gray, K Tourpali, Katja Matthes, L L Hood, Hauke Schmidt, Gabriel Chiodo, Remi ThieblemontAbstract:The surface response to the 11-yr solar cycle is assessed in ensemble simulations of the 20th century climate performed in the framework of the 5th phase of the Coupled Model Inter-Comparison Project (CMIP5). A lead/lag multiple linear regression analysis identifies a multi-model mean (MMM) global mean surface warming of about 0.07 K lagging the solar cycle by one to two years on average. The anomalous warming penetrates to approximately the first 80–100 m depth in the ocean. Solar signals in the troposphere show a similar time lag of one to two years and the strongest MMM warming is simulated in the tropics above 300 hPa. At the surface, the MMM response in a subset of models that show statistically significant global mean warming (CMIP5-SIG95) is characterized by an anomalous warming in the west equatorial Pacific Ocean and the Arctic, at one to two years after solar maximum. The Arctic warming is twice as strong as the global mean response and appears in winter months only. The surface warming in the equatorial Pacific Ocean is related to dynamical/thermodynamical processes. Different increase rates of global mean precipitation and atmospheric water vapor in response to a warmer surface lead to a weaker Walker circulation and anomalous westerly winds over the equatorial Pacific in years following solar maximum. Owing to atmosphere–ocean Coupling, the anomalous westerly winds cool the subsurface and warm the surface in the western equatorial Pacific by ∼ 0.14 K. The CMIP5-SIG95 MMM surface warming in the equatorial Pacific and Arctic is weak but qualitatively similar compared to solar signals in the HadCRUT4 dataset.
Gabriel Chiodo - One of the best experts on this subject based on the ideXlab platform.
-
solar signals in cmip 5 simulations effects of atmosphere ocean Coupling
Quarterly Journal of the Royal Meteorological Society, 2016Co-Authors: Stergios Misios, Daniel M Mitchell, L J Gray, K Tourpali, Katja Matthes, L L Hood, Hauke Schmidt, Gabriel Chiodo, Remi ThieblemontAbstract:The surface response to the 11-yr solar cycle is assessed in ensemble simulations of the 20th century climate performed in the framework of the 5th phase of the Coupled Model Inter-Comparison Project (CMIP5). A lead/lag multiple linear regression analysis identifies a multi-model mean (MMM) global mean surface warming of about 0.07 K lagging the solar cycle by one to two years on average. The anomalous warming penetrates to approximately the first 80–100 m depth in the ocean. Solar signals in the troposphere show a similar time lag of one to two years and the strongest MMM warming is simulated in the tropics above 300 hPa. At the surface, the MMM response in a subset of models that show statistically significant global mean warming (CMIP5-SIG95) is characterized by an anomalous warming in the west equatorial Pacific Ocean and the Arctic, at one to two years after solar maximum. The Arctic warming is twice as strong as the global mean response and appears in winter months only. The surface warming in the equatorial Pacific Ocean is related to dynamical/thermodynamical processes. Different increase rates of global mean precipitation and atmospheric water vapor in response to a warmer surface lead to a weaker Walker circulation and anomalous westerly winds over the equatorial Pacific in years following solar maximum. Owing to atmosphere–ocean Coupling, the anomalous westerly winds cool the subsurface and warm the surface in the western equatorial Pacific by ∼ 0.14 K. The CMIP5-SIG95 MMM surface warming in the equatorial Pacific and Arctic is weak but qualitatively similar compared to solar signals in the HadCRUT4 dataset.