Stratospheric temperature monitoring using a vibrational Raman lidar : Part 1: aerosols and ozone interferences

Lidar measurements of temperature for the upper troposphere and lower stratosphere are commonly derived by the Raman technique. Lidar signals derived from vibrational Raman processes have been subjected to numerous simulation tests to examine their sensitivity to the presence of aerosols and ozone in the atmosphere. The influence of aerosols characteristics (wavelength dependence of aerosol extinction and particle phase function) and of ozone concentration on Raman temperature profiles is estimated. Simulations indicate large temperature deviations for post-volcanic conditions. For a Raman backscatter at 607 nm, bias is below 1 K for a total optical depth less than 9 x 10(-3) in the case of a stratospheric contamination and less than 6 x 10(-3) for a tropospheric contamination. The effect of aerosols depends on phase function and a few parameters such as altitude, optical depth and the shape of the high-altitude cloud. The wavelength dependence of aerosol extinction has some influence only for severe post-volcanic conditions (Scattering Ratio, SR >2). For a Raman backscatter at 387 nm, bias is larger and can be significant even in background aerosol conditions. Changes in the ozone density profile lead to significant Raman temperature deviations only for some specific conditions. Results suggest that both aerosol and ozone corrections are necessary to obtain an accuracy better than the 1 K requested for most atmospheric applications.

The influence of elevated ultraviolet-B radiation (UV-B) on tissue quality and decomposition of loblolly pine (Pinus taeda L.) needles

Stratospheric ozone depletion is expected to elevate the influx of ultraviolet-B radiation (UV-B) to the biosphere. Increased levels of UV-B may, in turn, alter important ecosystem processes such as decomposition. Previous studies have shown that growth under elevated UV-B can alter leaf quality in angiosperm species and thereby indirectly change subsequent rates of leaf decay. In this experiment, we determined if elevated UV-B would alter the chemical composition and decay of needle tissue from two seed sources of the gymnosperm Pinus taeda L. Maryland and Virginia seed sources of P. taeda were grown in the field for 3 years beneath lampbanks supplying either ambient, low elevated or high elevated UV-B. These levels of UV-B corresponded to 0, 16 and 25% stratospheric ozone depletion at the experimental site in Beltsville, MD (39 degrees N). Needles were collected from six randomly chosen plants for each combination of seed source and UV-B level. The needle samples were analyzed for total C and N, UV-B absorbing compounds, and carbon fractions. Decay rates were also determined by measuring rates of CO(2) evolution from needle material decomposed under laboratory conditions. UV-B did not significantly alter the chemical composition of needles from the Virginia seed source. In contrast, needles from the Maryland seed source tended to have elevated lignin/N ratios and a lower holocellulose content when grown under the highest level of UV-B. Furthermore, while needles from the Virginia pines did not have UV-B altered decay rates, Maryland needles grown under low elevated UV-B conditions decomposed 36% more rapidly than needles from other treatments. Results from this experiment illustrate at least three characteristics about the indirect effect of UV-B on decomposition, (1) UV-B can modify decomposition of tissue from gymnosperms as well as angiosperms; (2) UV-B effects on tissue chemistry and decay may not only be species-specific but also seed-source specific; and (3) UV-B effects on decomposition may not increase with increasing UV-B dose.