Mid-latitude troposphere

Time scales of transport can also be applied to situations when no well-defined reservoirs can be defined. If the dominant transport process is advection by mean flow or sedimentation by gravity, the time scale characterizing the transport between two places is simply tadv = L/V where L is the distance and V the transport velocity. Given a t)q)ical wind speed of 20 m/s in the mid-latitude tropospheric westerlies, the time of transport around the globe would be about 2 weeks. 

Three regions of the atmosphere are seen to have significant zonal components of flow and thus of advection. The mid-latitude troposphere at the surface tends to exhibit westerly flow (i.e., flow from west to east) on the average. This region contains the familiar high- and low-pressure systems that cause periodicity in mid-latitude weather. Depending on the lifetime of the substances of concern, the motion in these weather systems may be important. 

Platt U. (2000) Reactive halogen species in the mid-latitude troposphere—recent discoveries. Water Air Soil Pollut. 123, 229-244. 

Platt, U., 2000 Reactive Halogen Species in the mid-Latitude Troposphere - Recent discoveries , in Wetter, Air, Soil Pollution, 123 229-224. 

The tropical regions of both of the hemispheres troposphere exhibit easterly flow called the trade winds. Finally the jet stream -sometimes described as a river of air - flows at mid-latitude of both hemispheres with velocities of 25 to 50 m/sec from west to east, often carrying material completely around the Earth at its altitude close to the tropopause. It is in this flow that balloonists attempt to circle the globe. 

Hebestreit, K., J. Stutz, D. Rosen, V. Matveiv, M. Peleg, M. Luria, and U. Platt, DOAS Measurements of Tropospheric Bromine Oxide in Mid-Latitudes, Science, 283, 55-57 (1999). 

The bulk of cloudiness is found in the lowest level of the atmosphere, which is called the troposphere. The thickness of the troposphere is 8 km at high latitudes, 12km at mid-latitudes, and 16km at low latitudes (Buseck and Schwartz 2004). In our simulations, we assumed a 12 km troposphere and a lapse rate of 6.5°C/km (Lide, 1994). We also assumed a starting point of 0.0 km and 25 °C (Fig. 5.8) for our two solutions, which were then lofted to colder (higher) altitudes. 

Figure 17.5 also shows the track of flight 10 during PEACE-B on 14 May 2002. A mid-latitude cyclone was located over central China on 13 May. Warm and moist southerly winds in the lower troposphere intensified ahead of this surface cyclone over southern China, converging into a fi ont extending between 20°N, 100°E and 30°N, 115°E. Deep convective clouds, with tops above 10 km around 30°N, 105-120°E, are found in an infrared (IR) image obtained by the Geostationary... 

Because both UV radiation fluxes and water vapor concentrations are largest in the tropics and in the southern hemisphere, the levels of OH generally have their maxima in the lower troposphere in these regions and seasons (Figure 1). Also, because much O3 is produced in and exported from polluted areas, its concentrations generally have maxima in the northern hemisphere mid-latitude summer (Figure 1). 

The first mid-latitude demonstration of reactive halogen chemistry in the troposphere was made downwind of salt pans in the Dead Sea area, where... 

The presence of 0.5-2 pmol moU BrO in the troposphere would have a considerable effect on atmospheric chemistry as shown by the model smdies that we discussed in Section 4.02.4.3. It could help explain events of upper troposphere near-zero O3 mixing ratios which have been found by Kley et al. (1996) over the equatorial Pacific. A similar event was discussed by Davies et al. (1998) where near-zero O3 concentrations were encountered in the mid-latitude upper troposphere. According to trajectory smdies, the air-mass with low ozone was advected from the subtropical upper troposphere. 

Hebestreit K., Stutz J., Rosen D., Matveiv V., Peleg M., Luria M., and Platt U. (1999) DOAS measurements of tropospheric bromine oxide in mid-latitudes. Science 283, 55-57. 

The concentration of atmospheric radionuclides has a special distribution which depends on latitudes and altitudes. Cosmogenic radionuclides have higher production rates in the stratosphere than in the troposphere, because of a higher intensity of cosmic rays in the stratosphere. Fallout nuclides have higher concentrations in mid-latitude of the Northern Hemisphere, because most atmospheric nuclear explosion experiments were made there. 

Figure 1. (a) Averaged results of concentration measurements at various altitudes for tropospheric particles of radius >2 x 10 m in continental air at mid-latitudes (a summary of data from Ref. 5). 

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