Dominikus Heinzeller

Numerical Simulation of Surface Energy and Water Balances over a Semiarid Grassland Ecosystem in the West African Savanna

To understand surface energy exchange processes over the semiarid regions in West Africa, numerical simulations of surface energy and water balances were carried out using a one-dimensional multilayer atmosphere-SOil-VEGetation (SOLVEG) model for selected days of the dry and rainy seasons over a savanna grassland ecosystem in Sumbrungu in the Upper East region of Ghana. The measured Bowen ratio was used to partition the residual energy into the observed sensible heat flux ( ) and latent heat flux (LE) in order to investigate the impact of the surface energy closure on model performance. The results showed that the model overall reproduced the diurnal changes in the observed energy fluxes, especially the net radiation (Rn), compared to half-hourly eddy covariance flux measurements, for the study periods. The performance measure in terms of the correlation coefficient ( ), centred root mean square error (RMSE), and normalized standard deviation (σ) between the simulated and LE and their corresponding uncorrected observed values ranged between R = 0.63–0.99 and 0.83–0.94, RMSE = 0.88–1.25 and 0.88–1.92, and = 0.95–2.23 and 0.13–2.82 for the dry and rainy periods respectively, indicating a moderate to good model performance. The partitioning of and LE by SOLVEG was generally in agreement with the observations during the dry period but showed clear discrepancies during the rainy period, particularly after rainfall events. Further sensitivity tests over longer simulation periods (e.g., 1 year) are required to improve model performance and to investigate seasonal exchanges of surface energy fluxes over the West African Savanna ecosystems in more details.

Explicit Convection and Scale-Aware Cumulus Parameterizations: High-Resolution Simulations over Areas of Different Topography in Germany

AbstractAn increase in the spatial resolution of regional climate model simulations improves the representation of land surface characteristics and may allow the explicit calculation of important physical processes such as convection. The present study investigates further potential benefits with respect to precipitation, based on a small ensemble of high-resolution simulations with WRF with grid spacings up to 1 km. The skill of each experiment is evaluated regarding the temporal and spatial performance of the simulation of precipitation of one year over both a mountainous region in southwestern Germany and a mainly flat region in northern Germany. This study allows us to differentiate between the impact of grid spacing, topography, and convection parameterization. Furthermore, the performance of a state-of-the-art convection parameterization scheme in the gray zone of convection is evaluated against an explicit calculation of convection only. Our evaluation demonstrates the following: high-resolution si...

Simulation of the Rain Belt of the West African Monsoon (WAM) in High Resolution CCLM Simulation

We present the results of our regional climate modeling experiments conducted on ForHLR1, using the consortium for small-scale modeling (COSMO) regional climate model CCLM over West Africa. This work is embedded in the context of the West African Science Service Center on Climate Change and Adapted Land Use (WASCAL) research project. We conduct nested runs at 50 and 12 km resolution driven by ERA-Interim data to assess the modeled location and intensity of the tropical rainbelt over West Africa for the period 1979–2013. The simulation period includes the years 1983 and 1999 with observed extreme anomalies (dry as well as wet). These anomalies are captured by our experiment: The model reproduces the observed zonal-mean variations in precipitation within the range of comparable regional climate model (RCM) studies, but reduces the dry bias in the Golf of Guinea and shows an increased accuracy for the driest years in general. Based on these encouraging results, we are currently extending our work towards historical climate runs and climate projections for an improved understanding of the different processes involved in the West Africa climate system and their role in generating extreme climatic conditions.

Anthropogenic Aerosol Emissions and Rainfall Decline in Southwestern Australia: Coincidence or Causality?

AbstractIt is commonly understood that the observed decline in precipitation in southwestern Australia during the twentieth century is caused by anthropogenic factors. Candidates therefore are changes to large-scale atmospheric circulations due to global warming, extensive deforestation, and anthropogenic aerosol emissions—all of which are effective on different spatial and temporal scales. This contribution focuses on the role of rapidly rising aerosol emissions from anthropogenic sources in southwestern Australia around 1970. An analysis of historical long-term rainfall data of the Bureau of Meteorology shows that southwestern Australia as a whole experienced a gradual decline in precipitation over the twentieth century. However, on smaller scales and for the particular example of the Perth catchment area, a sudden drop in precipitation around 1970 is apparent. Modeling experiments at a convection-resolving resolution of 3.3 km using the Weather Research and Forecasting (WRF) Model version 3.6.1 with th...

Anthropogenic Aerosol Emissions and Rainfall Decline in South-West Australia

It is commonly understood that the observed decline in precipitation in South-West Australia during the twentieth century is caused by anthropogenic factors. In our project wa-aero on ForHLR1, we focus on the role of rapidly rising aerosol emissions from anthropogenic sources in South-West Australia around 1970. An analysis of historical longterm rainfall data of the Bureau of Meteorology shows that South-West Australia as a whole experienced a gradual decline in precipitation over the twentieth century. However, on smaller scales and for the particular example of the Perth catchment area, a sudden drop in precipitation around 1970 is apparent. Modelling experiments at a convection-resolving resolution of 3.3 km using the Weather and Research Forecasting (WRF) model version 3.6.1 with the aerosol-aware Thompson-Eidhammer microphysics scheme are conducted for the period 1970–1974. A comparison of four runs with different prescribed aerosol emissions and without aerosol effects demonstrates that tripling the pre-1960s atmospheric CCN and IN concentrations, as suggested by air-borne measurements, can suppress precipitation by 2–9 %, depending on the area and the season. An extended version of the results presented here was accepted for publication in the Journal of Climate in June 2016.