Transport

In general, the abundance of a constituent at a fixed point in space is determined by a combination of chemical production, chemical loss, and transport of the constituent. To highlight the effects of transport of O, on the O, distribution, we estimate the Ov abundance in the stratosphere in the absence of transport. In this case, the continuity equation for O, is:

'dt where Pn is the production rate (molecules cm ' s ') and Ln is the loss frequency (1 s~') of O,. Using daytime-averaged P0k and L() from a model and assuming that the time rate of change of O, (¿)[OJ/8f) is equal to zero, we can solve for [OJ;, = P„JL0 and thereby obtain an estimate of the "steady-state" abundance of O, in the absence of transport of O,. Figure 5.1 plots annually averaged [Or]ss, which we will call the "no transport" case. It should be noted that only transport of O, has been neglected; the effects of transport of other species, such as NO,, CI, and other long-lived species, are included in Plt and ¿() In addition, PiK and L() are both functions of the distribution of Or: Figure 5.1 is calculated using P(} and L0 that incorporate realistic background abundances of O,.

Figure 5.2 shows the annually and zonally averaged "transported" O, distribution—by "transported" we mean that O, is subject to the full continuity equation, including transport. This distribution is quite similar to the satellite-derived distribution shown in Figure 1,2a in Chapter 1.

Figure 5.3, a plot of the difference between Figures 5.1 and 5.2, shows the influence of the transport of O,. Above about 30 km there is virtually no difference between the O, fields. At these altitudes the rate of transport of O, is negligible compared to the chemical production and loss rates, and the system is in either diurnal or photochemical steady state. It should be noted that transport is still important insof ar as it affects the abundances of CI,,, NO,, etc., that regulate the loss rate of O,.

Below -30 km (~1() h Pa), however, the difference between the "transported" and "no transport" Ot fields is significant, demonstrating the role that transport plays in determining the O, distribution. There are positive values in the tropical lower and to cl

0 0

Post a comment