Climate of the control runs





The model comprises the coupled atmosphere-ocean components and the dynamic global vegetaion model LPJ. The time-series below are showing three different control runs. The black and the red curve refer to different coupling techniques. The periodically synchronous coupling technique (black curve) means that the atmosphere is temporarily switched off in order to save computer resources. These two experiments were performed with a fixed vegetation. Additionally, another run was performed including the dynamic global vegetaion model LPJ (blue curves). Regarding the sea surface temperatures, and the atlantic meridional overturning function as well (an important climate factor which controls the oceanic heat transport), a strong variability is found in all the models. There is, however, no long-term drift in the parameters recognizable.


The following figures are showing results from the model climate, averaged over the period of the first 2000 simulated years.

Figure 1: Summer- und winter- temperature [° K.]
The model reproduces the known global pattern of near surface air temperatures. The global oceanic circulation is responsible for the strong positive temperature anomalies in the North Atlantic and northern Europe (global Conveyor belt, Broecker, 1985; Gordon, 1986). This anomaly particularly well dveloped during the winter season, when deep convection in the North Atlantic is at its maximum.

Summer - temperature

enlarge

Winter - temperature

enlarge


Yearly mean precipitation

enlarge

In accordance with observed data strongest precipitation is found over oceanic areas. Maximum values indicate the intertropical convergence zone along the equator. Continents are marked by generally lower precipitation with minimum values around the subtropics (e.g. sahara desert).


enlarge

Likewise, the sea-surface temperatures are reproduced very well. A strong positive anomaly is developed in the northern North Atlantic (compared to the North Pacific) as a direct consequence of the model Gulf Stream. Highest temperatures are seen in the western Pacific indicating the western pacific warm pool. Along the nothern coast of South America moderately lower temperatures indicate the upwelling of colder deep waters.


The observed large-scale patterns are further confirmed by the oceanic heat fluxes. Because of the high overturning rates in the Atlantic Ocean, strongest negative anomalies are exhibited around the northern deep water production sites, where the ocean loses large quantities of heat to the atmosphere. By contrast, an overall positive bilance is registered in the South Atlantic. Strongest heat-uptake is concentrated in regions with strong upwelling (e.g. near the equatorial eastern Africa).
A weaker oceanic heat transport is found in the Pacific Ocean, resulting in a more symmetric heat flux pattern around the equator with maximum values along the tropical divergence zone.

enlarge

Positve values (red) indicate heat-uptake, negative values indicate heat loss (blue) of the ocean.


Compared to Pacific Ocean, the Atlantic Ocean ist rather well ventilated. Maximum overturning rates exceeding 18 Sv at 30°N and 1500m waterdepth demonstrate the dominance of North Atlantic Deep Water (NADW). The modeled overturning rates appear slightly to high with respect to NADW and slightly to low with respect to the underlying Antarctic Bottom Water (AABW). Positive values indicate clockwise rotation.

enlarge


In strong contrast to this, considerably weaker ventilation is indicated in the Pacific Ocean. The upper water column is dominated by strong Ekman cells. Northward entraining AABW constitutes the only source of Deep Water.Positive values indicate clockwise rotation.

enlarge


The overall pattern of global oceanic surface- and deep- water circulation results in significantly different heat transports of major ocean basins. Due to the well-developed atlantic meridional overturning circulation, the heat ransports north of 30°N are strongest in the Atlantic Ocean.

enlarge

under construction