Peter H. Zimmermann

Evaluation and intercomparison of global atmospheric transport models using 222Rn and other short‐lived tracers

Simulations of 222Rn and other short-lived tracers are used to evaluate and intercompare the representations of convective and synoptic processes in 20 global atmospheric transport models. Results show that most established three-dimensional models simulate vertical mixing in the troposphere to within the constraints offered by the observed mean 222Rn concentrations and that subgrid parameterization of convection is essential for this purpose. However, none of the models captures the observed variability of 222Rn concentrations in the upper troposphere, and none reproduces the high 222Rn concentrations measured at 200 hPa over Hawaii. The established three-dimensional models reproduce the frequency and magnitude of high-222Rn episodes observed at Crozet Island in the Indian Ocean, demonstrating that they can resolve the synoptic-scale transport of continental plumes with no significant numerical diffusion. Large differences between models are found in the rates of meridional transport in the upper troposphere (interhemispheric exchange, exchange between tropics and high latitudes). The four two-dimensional models which participated in the intercomparison tend to underestimate the rate of vertical transport from the lower to the upper troposphere but show concentrations of 222Rn in the lower troposphere that are comparable to the zonal mean values in the three-dimensional models.

A global three-dimensional source-receptor model investigation using 85Kr

Abstract A global tropospheric tracer transport model is applied to an overall 85Kr emission database. 85Kr, an exclusively anthropogenic radioactive noble gas, is released by nuclear fuel recycling plants and it is suitable for computer model testing, because it has rather well-known sources and sinks. The simulation of the global 85Kr dispersion which started in 1945 produces a fairly accurate approximation of the global concentration distribution in the 1980s. This is demonstrated by comparing the calculations against measurements at several observation sites. Deviations between the simulation and the observed data can be attributed to the fact that the transport is based on long-term averaged meteorological data. In addition, there are uncertainties—especially interannual irregularities—in the emission sources. It is demonstrated how the seasonality at a receptor location is affected by a discontinuity in a source. An idealized source-receptor model experiment gives some general information about atmospheric travel times of signals from point sources around the Earth and agrees almost perfectly with earlier theoretical studies.

A 3 Dimensional Global Study of the Photochemistry of Ethane and Propane in the Troposphere: Production and Transport of Organic Nitrogen Compounds

Although catalysis by nitrogen oxides (NOx) is the pivotal process for ozone formation in the troposphere, nonmethane hydrocarbons (NMHC) affect tropospheric chemistry because they play an important role as the “fuel” for the oxidation processes leading to the formation of peroxy radicals. Another interaction between hydrocarbon and NOX chemistry causes the production of organic nitrates which serve as a temporary sink for NOX. In particular, peroxyacetyl nitrate (PAN) measured in the troposphere in mixing ratios comparable to those of NOX [Singh et al., 1991], can act as reservoir for NOX. Among the NMHC, the most abundant globally are ethane (C2H6 and propane (C3H8). They are known to have various anthropogenic and natural sources but our knowledge of the strength and distribution of their emissions is incomplete [Singh and Zimmerman, 1991].

Cumulus Cloud Vertical Transport Studies with the Moguntia Model

The global three dimensional tropospheric tracer transport model, which was presented at the previous ITM, has been further developed to include a cumulus convection scheme. The model is used for tracer transport in the context of air chemistry investigations.

Comparing CARIBIC and Satellite Data

The ultimate objective of the CARIBIC project is to create a database of in-situ measurements of a large number of trace species (~ 60) and aerosol properties in the upper troposphere and lower stratosphere (UTLS) which may be used to validate satellite measurements. Altogether 45 CARIBIC return flights were executed between November 1997 and May 2002 when the Boeing 767 of LTU International Airways was decommissioned. The CO and O3 data for all flights were checked and incorporated into the CARIBIC data bank established on the basis of CERA2 (Climate and Environmental data Retrieval and Archive system) database designed by PIK, DKRZ, and AWL A new CARIBIC container with an extended instrumentation is being built for an Airbus A340-600 of Lufthansa AG. It is hoped to resume the measurements in September 2003 and to continue them for a period of 10 years.

Individual Reports from GLOMAC Contributors

The Stockholm contribution to GLOMAC has been focused on the development of models to simulate the distribution of sulfur compounds (DMS, SO2 and aerosol sulfate) and nitrogen compounds (NO, HNO3, NO 3 − and PAN) in the global troposphere and on estimating the environmental impact of these distributions. The models include natural and anthropogenic sources, chemical transformations in the atmosphere, and wet and dry removal processes. During the first years, the main tool has been the transport model MOGUNTIA developed at the Max-Planck-Institute for Chemistry in Mainz. This model uses a coarse grid and is based on average meteorological conditions. During the past two years, the chemical schemes have been implemented in a meteorologically more advanced model (ECHAM) which uses meteorological parameters with higher spacial and temporal resolution.