Modelling mid-pliocene climate with COSMOS

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Abstract

In this manuscript we describe the experimental procedure employed at the Alfred Wegener Institute in Germany in the preparation of the simulations for the Pliocene Model Intercomparison Project (PlioMIP). We present a description of the utilized Community Earth System Models (COSMOS, version: COSMOS-landveg r2413, 2009) and document the procedures that we applied to transfer the Pliocene Research, Interpretation and Synoptic Mapping (PRISM) Project mid-Pliocene reconstruction into model forcing fields. The model setup and spin-up procedure are described for both the paleo- and preindustrial (PI) time slices of PlioMIP experiments 1 and 2, and general results that depict the performance of our model setup for mid-Pliocene conditions are presented. The mid-Pliocene, as simulated with our COSMOS setup and PRISM boundary conditions, is both warmer and wetter in the global mean than the PI. The globally averaged annual mean surface air temperature in the mid-Pliocene standalone atmosphere (fully coupled atmosphere-ocean) simulation is 17.35 °C (17.82 °C), which implies a warming of 2.23 °C (3.40 °C) relative to the respective PI control simulation. © Author(s) 2012.

Figures

  • Table 1. Plant functional types considered by JSBACH. These include different types of evergreen and deciduous forest, shrubs and grasses. The rightmost column indicates to which generalized vegetation type (forest or grass) a PFT contributes.
  • Fig. 1. Land-sea distribution on the ocean model grid as used in the PMIP3 PI control simulation (a) and the PlioMIP mid-Pliocene simulation (b) of experiment 2. There are two grid poles (white areas) which are located over Greenland and Antarctica. The nominal grid resolution of 3◦× 1.8◦ of the 122× 101 grid varies; it is high in polar regions and highest around Greenland. Both land-sea distributions are identical with the exception of the closure of the Hudson Bay and modifications in the West Antarctic in the case of the mid-Pliocene experiment. For clarity, only every second grid line is shown in the graph.
  • Fig. 2. Comparison of the orographic peaks elevation in units of m as used in the PI control simulation (a) to its mid-Pliocene counterpart (b), which has been generated from a coarse mid-Pliocene topography.
  • Fig. 3. Anomaly between the climatological SST forcings of the mid-Pliocene and PI control simulations of experiment 1 in units of ◦C. The green contours indicate the 90 % isoline of the absolute sea ice cover prescribed for the mid-Pliocene simulation. Shown are the forcings for the months January (a) and August (b).
  • Fig. 4. River directions on the hydrological model grid (0.5◦×0.5◦) of ECHAM5 for PI control (a) and adjusted to Pliocene topography (b). The colours indicate the flow direction at each grid point; ocean is indicated by white. In addition to the four main and diagonal directions, dark blue (O) marks grid cells where the water flow is directly into the ocean (coastal gridpoints).
  • Fig. 5. Vegetation forcing for PI control and Pliocene: Forest fractions for PI (a) and mid-Pliocene (b), grass fractions for PI (c) and midPliocene (d). See text for details.
  • Fig. 6. (a) Evolution of yearly average 2-m temperature in experiment 1. The atmosphere adjusts to the change in climate forcing very fast (cf. the inset that shows a monthly resolved time series of the first 10 simulation years), and reaches an equilibrium state in less than ten years. (b) Annual mean North Atlantic Ocean temperature and salinity at 700 m and 2200 m in the mid-Pliocene simulation of experiment 2. Starting point of the simulation is a temperature-adjusted PI control state at year 800 of the model time axis (see text for details). Output between model years 600 and 749 is missing, as indicated by the straight progression of the graph.
  • Fig. 8. Anomalies of SAT in ◦C between the mid-Pliocene and PI control runs of experiment 1. Shown are annual mean (a), boreal winter season (DJF) (b), and boreal summer season (JJA) (c), retrieved from a 30-yr climatology. Strong temperature anomalies over the Hudson Bay are caused by the change in the land-sea mask.

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APA

Stepanek, C., & Lohmann, G. (2012). Modelling mid-pliocene climate with COSMOS. Geoscientific Model Development, 5(5), 1221–1243. https://doi.org/10.5194/gmd-5-1221-2012

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