Modeling a 200-Yr Interruption of the Holocene Sapropel S1

2000 ◽  
Vol 53 (1) ◽  
pp. 98-104 ◽  
Author(s):  
Paul G. Myers ◽  
Eelco J. Rohling
Keyword(s):  
General Circulation Model ◽  
General Circulation ◽  
Deep Convection ◽  
Circulation Model ◽  
Intermediate Water ◽  
Gulf Of Lions ◽  
The Holocene ◽  
Circulation Mode ◽  
Oceanic General Circulation Model ◽  
Water Formation

AbstractAn oceanic general circulation model, previously used to simulate the conditions associated with the Holocene Sapropel S1, is used to simulate the effects of a climate deterioration (represented as a cooling event) on the sapropelic circulation mode. The enhanced cooling (2°–3°C) induces deep convection in the Adriatic and the Gulf of Lions and intermediate water formation in the Aegean, where in all cases there had previously been only stagnant unventilated waters. The depths of ventilation (to ∼1250 m) are in agreement with core data from this period. The short decadal timescales involved in modifying the sapropelic circulation suggest that such a climatic deterioration may be associated with the interruption of S1 between 7100 and 6900 14C yr B.P., which divided the sapropel into two subunits.

scholarly journals Convection–Climate Feedbacks in the ECHAM5 General Circulation Model: Evaluation of Cirrus Cloud Life Cycles with ISCCP Satellite Data from a Lagrangian Trajectory Perspective

2012 ◽  
Vol 25 (15) ◽  
pp. 5241-5259 ◽  
Author(s):  
Swati Gehlot ◽  
Johannes Quaas
Keyword(s):  
General Circulation Model ◽  
Model Evaluation ◽  
General Circulation ◽  
Trajectory Analysis ◽  
Deep Convection ◽  
Circulation Model ◽  
Life Cycles ◽  
Cirrus Clouds ◽  
Climate Feedbacks ◽  
Lagrangian Trajectory

Abstract A process-oriented climate model evaluation is presented, applying the International Satellite Cloud Climatology Project (ISCCP) simulator to pinpoint deficiencies related to the cloud processes in the ECHAM5 general circulation model. A Lagrangian trajectory analysis is performed to track the transitions of anvil cirrus originating from deep convective detrainment to cirrostratus and thin cirrus, comparing ISCCP observations and the ECHAM5 model. Trajectories of cloudy air parcels originating from deep convection are computed for both, the ISCCP observations and the model, over which the ISCCP joint histograms are used for analyzing the cirrus life cycle over 5 days. The cirrostratus and cirrus clouds originate from detrainment from deep convection decay and gradually thin out after the convective event over 3–4 days. The effect of the convection–cirrus transitions in a warmer climate is analyzed in order to understand the climate feedbacks due to deep convective cloud transitions. An idealized climate change simulation is performed using a +2-K sea surface temperature (SST) perturbation. The Lagrangian trajectory analysis over perturbed climate suggests that more and thicker cirrostratus and cirrus clouds occur in the warmer climate compared to the present-day climate. Stronger convection is noticed in the perturbed climate, which leads to an increased precipitation, especially on day−2 and −3 after the individual convective events. The shortwave and the longwave cloud forcings both increase in the warmer climate, with an increase of net cloud radiative forcing (NCRF), leading to an overall positive feedback of the increased cirrostratus and cirrus clouds from a Lagrangian transition perspective.

scholarly journals Importance of the Vertical Resolution in Simulating SST Diurnal and Intraseasonal Variability in an Oceanic General Circulation Model

2017 ◽  
Vol 30 (11) ◽  
pp. 3963-3978 ◽  
Author(s):  
Xuyang Ge ◽  
Wanqiu Wang ◽  
Arun Kumar ◽  
Ying Zhang
Keyword(s):  
Temperature Gradient ◽  
General Circulation Model ◽  
General Circulation ◽  
Circulation Model ◽  
Vertical Resolution ◽  
Vertical Temperature Gradient ◽  
Vertical Temperature ◽  
Sst Variability ◽  
Oceanic General Circulation Model ◽  
High Vertical Resolution

Abstract In this paper, the influence of high vertical resolution near the surface in an oceanic general circulation model in simulating the observed sea surface temperature (SST) variability is investigated. In situ observations of vertical temperature profiles are first used to quantify temperature variability with depth near the ocean surface. The analysis shows that there is a sharp vertical temperature gradient within the top 10 m of the ocean. Both diurnal and intraseasonal variabilities of the ocean temperatures are largest near the surface and decrease with the ocean depth. Numerical experiments with an oceanic general circulation model are next carried out with 1- and 10-m vertical resolutions for the upper ocean to study the dependence of the simulated SST and vertical temperature structure on the vertical resolution. It is found that the simulated diurnal and intraseasonal variabilities, as well as the associated vertical temperature gradient near the surface, are strongly influenced by the oceanic vertical resolution, with the 1-m vertical resolution producing a stronger vertical temperature gradient and temporal variability than the 10-m vertical resolution. These results suggest that a realistic representation of SST variability with a high vertical resolution in the upper ocean is required for a coupled atmosphere–ocean model to correctly simulate the observed tropical intraseasonal oscillations, including the Madden–Julian oscillation and the boreal summer monsoon intraseasonal oscillation, which are strongly linked with the underlying SST.

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