L.H. van Ulft

Extreme precipitation and climate gradients in Patagonia revealed by high-resolution regional atmospheric climate modeling

This study uses output of a high-resolution (5.5km) regional atmospheric climate model to describe the present-day (1979‐2012) climate of Patagonia, with a particular focus on the surface mass balance (SMB) of the Patagonian ice fields. Through a comparison with available in situ observations, it is shown that the model is able to simulate the sharp climate gradients in western Patagonia. The southern Andes are an efficient barrier for the prevalent atmospheric flow, generating strong orographic uplift and precipitation throughout the entire year. The model suggests extreme orographic precipitation west of the Andes divide, with annual precipitation rates of .5 to 34mw.e. (water equivalent), and a clear rain shadow east of the divide. These modeled precipitation rates are supportedqualitativelyby availableprecipitationstationsand SMBestimates on the ice fields derived from firn cores. For the period 1979‐2012, a slight atmospheric cooling at upper ice field elevations is found, leading to a small but insignificant increase in the ice field SMB.

Intercomparison of methods of coupling between convection and large-scale circulation. 1. Comparison over uniform surface conditions

Abstract As part of an international intercomparison project, a set of single‐column models (SCMs) and cloud‐resolving models (CRMs) are run under the weak‐temperature gradient (WTG) method and the damped gravity wave (DGW) method. For each model, the implementation of the WTG or DGW method involves a simulated column which is coupled to a reference state defined with profiles obtained from the same model in radiative‐convective equilibrium. The simulated column has the same surface conditions as the reference state and is initialized with profiles from the reference state. We performed systematic comparison of the behavior of different models under a consistent implementation of the WTG method and the DGW method and systematic comparison of the WTG and DGW methods in models with different physics and numerics. CRMs and SCMs produce a variety of behaviors under both WTG and DGW methods. Some of the models reproduce the reference state while others sustain a large‐scale circulation which results in either substantially lower or higher precipitation compared to the value of the reference state. CRMs show a fairly linear relationship between precipitation and circulation strength. SCMs display a wider range of behaviors than CRMs. Some SCMs under the WTG method produce zero precipitation. Within an individual SCM, a DGW simulation and a corresponding WTG simulation can produce different signed circulation. When initialized with a dry troposphere, DGW simulations always result in a precipitating equilibrium state. The greatest sensitivities to the initial moisture conditions occur for multiple stable equilibria in some WTG simulations, corresponding to either a dry equilibrium state when initialized as dry or a precipitating equilibrium state when initialized as moist. Multiple equilibria are seen in more WTG simulations for higher SST. In some models, the existence of multiple equilibria is sensitive to some parameters in the WTG calculations.

Contribution of Dynamic Vegetation Phenology to Decadal Climate Predictability

AbstractIn this study, the impact of coupling and initializing the leaf area index from the dynamic vegetation model Lund–Potsdam–Jena General Ecosystem Simulator (LPJ-GUESS) is analyzed on skill of decadal predictions in the fully coupled atmosphere–land–ocean–sea ice model, the European Consortium Earth System Model (EC-Earth). Similar to the impact of initializing the model with the observed oceanic state, initializing the leaf area index (LAI) fields obtained from an offline LPJ-GUESS simulation forced by the observed atmospheric state leads to a systematic drift. A different treatment of the water and soil moisture budget in LPJ-GUESS is a likely cause of this drift. The coupled system reduces the cold bias of the reference model over land by reducing LAI (and the associated evaporative cooling), particularly outside the growing season. The coupling with the interactive vegetation module implies more degrees of freedom in the coupled model, which generates more noise that can mask a portion of the ex...

Can We Explain the Observed Decrease in Secondary Inorganic Aerosol and Its Precursors Between 1990 and 2009 over Europe Using LOTOS-EUROS?

In this study we investigate the ability of the Chemistry Transport Model (CTM) LOTOS-EUROS to explain the observed decrease in secondary inorganic aerosol (SIA) and its precursors between 1990 and 2009 over Europe. The model explicitly accounts for cloud chemistry and aerosol thermodynamics. The results have shown that the model largely captures the observed trends in SIA and its precursors’ concentrations while it underestimates the interannual variability. Using a source-apportionment module the amount of SIA formed per unit emission was traced for a number of regions. The results show 20–50 % more efficient SO4 2− formation in 2009 compared to 1990, whereas the change in NO3 − formation per unit NOx emission is lower (−10 % to +20 %) for the same time period.