Synoptic scale

Hundreds to thousands of km - the synoptic scale, in which motions are those of whole weather systems. Advection is the dominant transport process. 

Going along with these spatial scales, we can define temporal scales as well. Micrometeoro-logic processes tend to be important for times less than an hour, mesoscale processes, up to about a day, and synoptic scale, a few days or more. 

The motion of substances on the synoptic scale is often assumed to be pure advection. The flux through a unit area perpendicular to the wind is simply the product of wind velocity and concentration. If F is flux, V the velocity, and c concentration. 

It is well established that in non-arid regions, precipitation is the primary means by which contaminating aerosols are removed from the atmosphere. Many chemical, physical, and meteorological parameters affect the micro, meso, and synoptic scale processes through which precipitation transports radioactive aerosols from atmosphere to ground. These parameters include the radioactivity component of the natural aerosols, the processes by which water vapor condenses and grows to raindrops, and the incorporation of the radioactive aerosol into the precipitation. Thus, the prediction of specific deposition from fundamental considerations has proved to be difficult because of the many uncertainties yet prevalent in these processes. Many attempts have been made to evaluate the deposition of these aerosols by empirical studies. 

The model tropopause is defined by a PV level of 3.5 pvu poleward of 20° latitude, and by a -2 K km 1 temperature lapse rate equatorward of 20° latitude. Consequently, in this study the troposphere is defined as the volume between the surface and the simulated tropopause. Because the model does not consider typical stratospheric chemical reactions explicitly, ozone concentrations are prescribed from 1-2 levels above the model tropopause up to the top of the model domain at 10 hPa. In both hemispheres we apply monthly and zonally averaged distributions from a 2D stratospheric chemistry model [31]. In the present version of the model, we use the simulated PV and the regression analysis of the MOZAIC data (Section 2) to prescribe ozone in the NH extratropical lower stratosphere, which improves the representation of ozone distributions influenced by synoptic scale disturbances [32, 33]. Furthermore, the present model contains updated reaction rates and photodissociation data [34]. 

Kentarchos, A.S., Roelofs, G.J., and Lelieveld, J. (1999) Simulation of extratropical synoptic scale stratosphere-troposphere exchange using a coupled chemistry-GCM Sensitivity to horizontal resolution, submitted to J. Atm. Sci. 

Local winds. Local (mesoscale) circulations and winds such as breezes, mountain-valley circulation, slope winds, foehns, boras, etc., along with the atmospheric processes on synoptic scale, play an important role in the formation of the climate on the coasts of the Black Sea. 

While some aspects of weather can be explained in terms of air mass movements, other synoptic-scale features of weather systems are associated with cyclones and anticyclones. Cyclones and anticyclones are large eddies (hundreds of kilometers across) in the atmosphere. Within their boundaries they influence and often control the direction and speed of wind and dominate the weather on a regional scale. They also influence the advective transport of air pollutants and subsequent air quality. On a global scale, cyclones and anticyclones contribute to tropospheric mixing. 

The data presented in weather maps are relevant to chemical transport both at the local scale, where local weather governs atmospheric mixing, and at the regional scale, where synoptic-scale circulation governs the long-range transport of chemicals across state and national boundaries. 

At scales smaller than the synoptic scale, topography and differences in the surface cover (e.g., forest, agricultural fields, open water, or urbanized land) influence local winds, precipitation, and temperature. One common example of a local effect due to surface cover is the sea breeze, which occurs because water bodies warm and cool more slowly than the land does. During the day in coastal areas, air over the land warms and rises more rapidly and is replaced by cooler air originating from over the water. The reverse may happen at night, as the land cools to a temperature lower than that of the water body,... 

For dispersion in flows with significant variation in direction and speed at different heights and different times, the only reliable modelling method is to track individual fluid particles or track many clouds of particles from the source. The former method is now used for regional and synoptic scale dispersion prediction from localised sources, such as nuclear accidents and volcanoes, e.g. Maryon and Buckland, 1995 [396], Assumptions have to be made about how atmospheric turbulence on scales less than 3Ax diffuses particles as they are advected by the resolved flow field on scale Ax. This method requires large computer resources and then can be computed in minutes. For studying critical events in UK urban areas this method should be considered. 

The atmospheric boundary layer (ABL) is that portion of the atmosphere where surface drag due to the motion of the air relative to the ground modifies synoptic-scale motions caused by horizontal pressure gradients, Coriolis forces, and buoyancy. The depth of the ABL is highly variable (50 to 2000 m), but it generally increases with proximity to the equator, with wind speed, and as the earth surface roughness, but it decreases... 

Applications of three-dimensional Baltic Sea circulation models, which encompass both synoptic scales and slowly varying long-term processes, were reported in Lehmann (1995), Lehmann and Hinrichsen (2000), Neumann et al. (2002), Schrum et al. (2003), and Lehmann et al. (2004). Long-term simulations covering the last century have been carried out by Meier... 

The horizontal airflow in the BL often consists of synoptic-scale (> 1000 km) and mesoscale (10-1000 km) circulations, and microscale ( 1 km) turbulence. Their time scales are days, 1 to 24 h, and less than 1 h, respectively. The impact of toxic dispersion on a synoptic scale or large mesoscale is generally not threatening to health, while for small mesoscale (< 100 km) and microscale, the impact can be life threatening because of accumulated doses over a relatively small area. Small-scale... 

The motion of substances on the synoptic scale is often assumed to be pure advection. The flux... 

Synoptic Scale. Motions of whole weather systems, on scales of hundreds to thousands of kilometers. 

Order of Magnitude of Atmospheric Quantities It is useful to estimate the order of magnitude of quantities in the equations of motion on the synoptic scale (systems having a spatial scale of 1000 km). Typical orders of magnitude of quantities are as follows (Mcllveen 1992) ... 

L is the horizontal distance over which there is a substantial change in the pressure or wind field. Ap is a typical horizontal pressure gradient for synoptic weather systems. The vertical pressure change is just the hydrostatic head of air from the surface to the tropopause. (In the spirit of order of magnitude, we estimate this as 1000 mbar rather than the accurate 900 mbar.) The time scale of I day is set by the Earth s rate of rotation. Moreover, the observed timescale of synoptic scale weather systems is about one day such systems take days rather than hours to form and dissipate. 

The domain of an atmospheric model—that is, the area that is simulated—varies from a few hundred meters to thousands of kilometers (Table 25.1). The computational domain usually consists of an array of computational cells, each having a uniform chemical composition. The size of these cells, that is, the volume over which the predicted concentrations are averaged, determines the spatial resolution of the model. Variation of concentrations at scales smaller than the model resolution cannot easily be resolved. For example, concentration variations over the Los Angeles basin cannot be described by a synoptic scale model that treats the entire area as one computational cell of uniform chemical composition. 

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