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Common parametrization models for cloud microphysical processes use condensate mass density and/or particle number density as prognostic properties. However, other moments of the particle size distribution can likewise be chosen for prediction. This study deals with parametrization models with one and two, respectively, prognostic moments for the sedimentation of drop ensembles. The spectral resolving model defines the reference solution.
The evolution of the vertical profiles of liquid water content, drop number density and rain rate strongly depend on the choice of the prognostic moments in the parametrization models. In models with a single prognostic moment, its vertical profile is copied by all other moments. The moment of most physical pertinence is recommended for prediction. In models with two prognostic moments, the vertical profiles of all moments differ. The orders of the prognostic moments should be chosen close to the order of moments of highest relevance. Otherwise large errors occur. For example, comparison of modelled versus observed radar reflectivity (6th moment with respect to diameter) does not tell much about the quality of other properties if reflectivity is diagnosed from for example, number density and mass density. Furthermore, mass conservation is fulfilled only if mass density is forecasted. 相似文献
The evolution of the vertical profiles of liquid water content, drop number density and rain rate strongly depend on the choice of the prognostic moments in the parametrization models. In models with a single prognostic moment, its vertical profile is copied by all other moments. The moment of most physical pertinence is recommended for prediction. In models with two prognostic moments, the vertical profiles of all moments differ. The orders of the prognostic moments should be chosen close to the order of moments of highest relevance. Otherwise large errors occur. For example, comparison of modelled versus observed radar reflectivity (6th moment with respect to diameter) does not tell much about the quality of other properties if reflectivity is diagnosed from for example, number density and mass density. Furthermore, mass conservation is fulfilled only if mass density is forecasted. 相似文献
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The sulfate-CCN-cloud albedo effect 总被引：7，自引：0，他引：7
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ULRIKE DUSEK DAVID S. COVERT ALFRED WIEDENSOHLER CHRISTIAN NEUSÜSS DIANA WEISE WILL CANTRELL 《Tellus. Series B, Chemical and physical meteorology》2003,55(1):35-53
In this work we propose and test a method to calculate cloud condensation nuclei (CCN) spectra based on aerosol number size distributions and hygroscopic growth factors. Sensitivity studies show that this method can be used in a wide variety of conditions except when the aerosol consist mainly of organic compounds. One crucial step in the calculations, estimating soluble ions in an aerosol particle based on hygroscopic growth factors, is tested in an internal hygroscopic consistency study. The results show that during the second Aerosol Characterization Experiment (ACE-2) the number concentration of inorganic ions analyzed in impactor samples could be reproduced from measured growth factors within the measurement uncertainties at the measurement site in Sagres, Portugal.
CCN spectra were calculated based on data from the ACE-2 field experiment at the Sagres site. The calculations overestimate measured CCN spectra on average by approximately 30%, which is comparable to the uncertainties in measurements and calculations at supersaturations below 0.5%. The calculated CCN spectra were averaged over time periods when Sagres received clean air masses and air masses influenced by aged and recent pollution. Pollution outbreaks enhance the CCN concentrations at supersaturations near 0.2% by a factor of 3 (aged pollution) to 5 (recent pollution) compared to the clean marine background concentrations. In polluted air masses, the shape of the CCN spectra changes. The clean spectra can be approximated by a power function, whereas the polluted spectra are better approximated by an error function. 相似文献
CCN spectra were calculated based on data from the ACE-2 field experiment at the Sagres site. The calculations overestimate measured CCN spectra on average by approximately 30%, which is comparable to the uncertainties in measurements and calculations at supersaturations below 0.5%. The calculated CCN spectra were averaged over time periods when Sagres received clean air masses and air masses influenced by aged and recent pollution. Pollution outbreaks enhance the CCN concentrations at supersaturations near 0.2% by a factor of 3 (aged pollution) to 5 (recent pollution) compared to the clean marine background concentrations. In polluted air masses, the shape of the CCN spectra changes. The clean spectra can be approximated by a power function, whereas the polluted spectra are better approximated by an error function. 相似文献
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Conceptual box models of the interhemispheric thermohaline circulation are studied with respect to bifurcations. Freshwater fluxes are the main control parameters of the system: they determine the stable states and transitions between stable states of the large-scale thermohaline circulation. In this study of interhemispheric box models both numerical and analytical methods are used to investigate transition mechanisms of the thermohaline circulation. The box model examined first is an interhemispheric four-box model. It is shown that the two bifurcations where the present THC can become unstable, the saddle-node and the Hopf bifurcation, depend in a different way on hemispheric freshwater fluxes. A reduction of the model variables leads to the conclusion that two fixed freshwater fluxes between three surface boxes are the model feature responsible for the bifurcation behaviour found. The significance of the Hopf bifurcation for the stability of the thermohaline circulation is discussed. 相似文献
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ULRIKE BURKHARDT 《地球，A辑:动力气象学与海洋学》1999,51(2):289-303
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ULRIKE KIENEL CHRISTINE SIEGERT JÜRGEN HAHNE 《Boreas: An International Journal of Quaternary Research》1999,28(1):181-193
A Late Quaternary permafrost profile from the Labaz Lake area (Taymyr Peninsula, Central Siberia) has been investigated using analyses of diatoms, pollen, sedimentology and geochemistry. A sedimentation gap for the termination of the Pleistocene and the start of lacustrine sedimentation in the Boreal can be inferred. At that time shallow-lake conditions prevailed and a connection to the Labaz Lake is probable. The diatom data provide indications for the assessment of the Holocene environmental development of the study site in more detail. The most favourable climatic conditions and comparatively higher water level stands are inferred for the early Atlantic. Towards the end of this period the gradual transition to a wetland with poor-fen character took place. Within the Subboreal there was a short episode with mild climate conditions. At that time the last trees occurred in the Labaz Lake area and somewhat higher water level stands were likely. The Subatlantic climate deterioration led to further drying up of the wetland along with a lowering of water pH and permafrost aggradation. The transition from a locality with low-centre to one with high-centre polygons is still underway. 相似文献
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