An integrated forecasting and data assimilation system has been and is continuing to be developed by the Meteorological Research Branch (MRB) in partnership with the Canadian Meteorological Centre (CMC) of Environment Canada. Part I of this two-part paper motivates the development of the new system, summarizes various considerations taken into its design, and describes its main characteristics.

https://journals.ametsoc.org/doi/pdf/10.1175/1520-0493%281998%29126%3C1373%3ATOCMGE%3E2.0.CO%3B2

The Operational CMC–MRB Global Environmental Multiscale (GEM) Model. Part I: Design Considerations and Formulation

Processes in the climate system that can either amplify or dampen the climate response to an external perturbation are referred to as climate feedbacks. Climate sensitivity estimates depend critically on radiative feedbacks associated with water vapor, lapse rate, clouds, snow, and sea ice, and global estimates of these feedbacks differ among general circulation models. By reviewing recent observational, numerical, and theoretical studies, this paper shows that there has been progress since the Third Assessment Report of the Intergovernmental Panel on Climate Change in (i) the understanding of the physical mechanisms involved in these feedbacks, (ii) the interpretation of intermodel differences in global estimates of these feedbacks, and (iii) the development of methodologies of evaluation of these feedbacks ( or of some components) using observations. This suggests that continuing developments in climate feedback research will progressively help make it possible to constrain the GCMs' range of climate feedbacks and climate sensitivity through an ensemble of diagnostics based on physical understanding and observations.

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How Well Do We Understand and Evaluate Climate Change Feedback Processes

Toward the end of the Cirrus Regional Study of Tropical Anvils and Cirrus Layer–Florida Area Cirrus Experiment (CRYSTAL–FACE) field campaign held during July 2002, high concentrations of Saharan dust, which can serve as cloud condensation nuclei (CCN), giant CCN (GCCN), and ice-forming nuclei (IFN) were observed over the peninsula of Florida. To investigate the impacts of enhanced aerosol concentrations on the characteristics of convective storms and their subsequent anvil development, sensitivity tests are conducted using the Regional Atmospheric Modeling System (RAMS) model, in which the initialization profiles of CCN, GCCN, and IFN concentrations are varied. These variations are found to have significant effects on the storm dynamics and microphysical processes, as well as on the surface precipitation. Updrafts are consistently stronger as the aerosol concentrations are increased. The anvils cover a smaller area but are better organized and have larger condensate mixing ratio maxima in the cas...

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Impacts of Nucleating Aerosol on Florida Storms. Part I: Mesoscale Simulations

A general climatology of the main mechanisms involved in Mediterranean cyclogenesis is presented. A diagnostic study of both composite means and case studies is performed to analyze processes occurring in different seasons, and in different cyclogenetic regions within the same season. It is shown that cyclones that developed over the three most active areas in winter—the Gulf of Genoa, the Aegean Sea, and the Black Sea—are essentially subsynoptic lows, triggered by the major North Atlantic synoptic systems being affected by local orography and/or low-level baroclinicity over the northern Mediterranean coast. It is also suggested that cyclones in two, or all three, of these regions often occur consecutively, linked to the same synoptic system. In spring and summer, thermally induced lows become progressively more important, despite the existence of other factors, such as the Atlas Mountains contributing to lee cyclogenesis in northern Africa, or the extension of the Asian monsoon into the eastern ...

Climatology of Cyclogenesis Mechanisms in the Mediterranean

Large-scale changes in land cover affect near- surface energy, moisture and momentum fluxes owing to changes in surface structure (referred to as biogeophysical effects) and the atmospheric CO2 concentration owing to changes in biomass (biogeochemical effects). Here we quan- tify the relative magnitude of these processes as well as their synergisms by using a coupled atmosphere-biosphere-ocean model of intermediate complexity. Our sensitivity studies show that tropical deforestation tends to warm the planet because the increase in atmospheric CO2 and hence, at- mospheric radiation, outweighs the biogeophysical effects. In mid and high northern latitudes, however, biogeophysi- cal processes, mainly the snow-vegetation-albedo feedback through its synergism with the sea-ice-albedo feedback, win over biogeochemical processes, thereby eventually leading to a global cooling in the case of deforestation and to a global warming, in the case of afforestation.

/pdf/biogeophysical-versus-biogeochemical-feedbacks-of-large-ee8cq9ow2g.pdf

Biogeophysical versus biogeochemical feedbacks of large‐scale land cover change

A simple method is developed for computing the interactions among various factors influencing the atmospheric circulations. It is shown how numerical simulations can be utilized to obtain the pure contribution of any factor to any predicted field, as well as the contributions due to the mutual interactions among two or more factors. The mathematical basis for n factors is developed, and it is shown that 2n simulations are required for the separation of the contributions and their possible interactions. The method is demonstrated with two central factors, the topography and surface fluxes, and their effect on the rainfall distribution for a cyclone evolution in the Mediterranean.

Factor Separation in Numerical Simulations.

The roles of topography, convection, sensible and latent heat fluxes in Alpine lee cyclogenesis are investigated. The adoption of a newly developed factor separation method allows the identification of the contributions of each of these processes as well as their synergistic effects. Topographical blocking is the dominant factor in the first and most rapid phase of the cyclone deepening. This is followed by the convection contribution at the 2nd but slower phase. Local moisture flux is dominant in the 3rd phase accompanied by a significant cyclolytic contribution by the Alps. Between the 1st and the 2nd phases of deepening, the synergistic effect of convection induced by the mountains plays an important role in the deepening at a time when the convection independent of mountains has not become yet so active. Coarser horizontal resolutions still capture these features, although to a lesser extent. Model simulation results are shown to be strongly dependent upon the chosen set of factors. As the number of factors increases, a specific contribution diminishes because synergistic terms with the new factors are extracted from the contribution of the specific factor under investigation. Another interesting conclusion is that the elimination of an important factor from the investigation will not remove its contribution. It will reappear and be attributed to another factor which is the most synergistic to the important factor. The spread of the cyclones' centers in the model simulations is shown to be a powerful tool in understanding the effects of different factors on the evolution of the model solutions. For instance, convection moves the cyclone to the east northeast while topography ties the cyclone to the lee of the Alps. The sea moisture fluxes tend to move the cyclone toward the warm bodies of water. DOI: 10.1034/j.1600-0870.1996.t01-1-00002.x

A multi-stage evolution of an ALPEX cyclone

The contribution of a particular process is shown to be strongly dependent upon the other processes under investigation because of synergistic contributions. In general, as the number of relevant factors being investigated increases, the role of any specific factor diminishes because the synergistic interactions with the new factors are extracted. This is illustrated with the variations of the topographic role in the impressive lee cyclone deepening event on 3–5 March 1982 during the Alpine Experiment. When latent heat release, latent heat flux, and sensitive heat flux enter into our comparative study, the topographic contribution to the surface pressure lee cyclone deepening gradually diminishes down to 50% or more.

Can Sensitivity Studies Yield Absolute Comparisons for the Effects of Several Processes

Four typica Eastern Mediterranean (EM) winter cyclones were simulated, using the NCAR/PSU numerical mesoscale model. They all show a tendency for a sub-synoptic cyclone regeneration over the Mediterranean sea, south of the Cyprus island. This phenomenon is commonly referred to as a 'Cyprus Low', and its origin/mechanisms are investigated. A sensitivity study was carried out to isolate the effects of topography and surface fluxes on the 'Cyprus Low' development. A recently developed factor separation method was implemented, allowing a quantitative comparison between the contributions of topography and sea surface fluxes along with their synergistic effect to the cyclone's pressure fall. It is shown that the original cyclone, arriving from the west, was mainly influenced by the Turkish mountains whereas the Cyprus development was primarily induced by the Mediterranean sea fluxes, Consequently, a distinct boundary-layer vorticity maximum was found in the 'Cyprus Low', in contrast to the original cyclone which had a mid-tropospheric dominant vorticity centre. Tracks, vorticities, pressure falls and precipitation patterns all indicate the distinct development and mechanisms of eastern Mediterranean cyclogenesis.

Role of sea fluxes and topography in eastern Mediterranean cyclogenesis

The contributions of boundary factors, which may be considered to be independent of the physics or the dynamics of the mesoscale model, are explored in a consistent approach for a widely investigated Alpine Experiment (AL-PEX) lee cyclogenesis case. The roles of the lateral boundaries and the initial fields in conjunction with that of the topography, as well as their possible nonlinear interactions in various model settings, are calculated with the aid of the recently developed factor separation method. Focus is given to the influences of the extent of the model domain and of the running period prior to the climax of the lee cyclone development during 36 March 1982. It is shown that the initial conditions are dominant in the first 915 h, during which time the topography and lateral boundaries play negative roles because of the adjusting processes. The nonlinear interaction BI between lateral boundaries (B) and the initial conditions (I) was found to be the major contributor to the cyclone deepe...

U. Stein

Papers

Factor Separation in Numerical Simulations.

A multi-stage evolution of an ALPEX cyclone

Can Sensitivity Studies Yield Absolute Comparisons for the Effects of Several Processes

Role of sea fluxes and topography in eastern Mediterranean cyclogenesis

The Relative Roles of Lateral Boundaries, Initial Conditions, and Topography in Mesoscale Simulations of Lee Cyclogenesis