Showing papers by "Climate Monitoring and Diagnostics Laboratory published in 1999"

On Rayleigh Optical Depth Calculations

Abstract: Many different techniques are used for the calculation of Rayleigh optical depth in the atmosphere. In some cases differences among these techniques can be important, especially in the UV region of the spectrum and under clean atmospheric conditions. The authors recommend that the calculation of Rayleigh optical depth be approached by going back to the first principles of Rayleigh scattering theory rather than the variety of curve-fitting techniques currently in use. A survey of the literature was conducted in order to determine the latest values of the physical constants necessary and to review the methods available for the calculation of Rayleigh optical depth. The recommended approach requires the accurate calculation of the refractive index of air based on the latest published measurements. Calculations estimating Rayleigh optical depth should be done as accurately as possible because the inaccuracies that arise can equal or even exceed other quantities being estimated, such as aerosol optica...

Influence of El Niño on the equatorial Pacific contribution to atmospheric CO 2 accumulation

Abstract: The equatorial oceans are the dominant oceanic source of CO2 to the atmosphere, annually amounting to a net flux of 0.7–1.5 Pg (1015 g) of carbon, up to 72% of which emanates from the equatorial Pacific Ocean1,2,3. Limited observations indicate that the size of the equatorial Pacific source is significantly influenced by El Nino events4,5,6,7,8,9,10, but the effect has not been well quantified. Here we report spring and autumn multiannual measurements of the partial pressure of CO2 in the surface ocean and atmosphere in the equatorial Pacific region. During the 1991–94 El Nino period, the derived net annual sea-to-air flux of CO2 was 0.3 Pg C from autumn 1991 to autumn 1992, 0.6 Pg C in 1993, and 0.7 Pg C in 1994. These annual fluxes are 30–80% of that of 1996, a non-El-Nino year. The total reduction of the regional sea-to-air CO2 flux during the 1991–94 El Nino period is estimated to account for up to one-third of the atmospheric anomaly (the difference between the annual and long-term-average increases in global atmospheric CO2 content) observed over the same period.

A comparison of observations and model simulations of NOx/NOy in the lower stratosphere

Abstract: Extensive airborne measurements of the reactive nitrogen reservoir (NOY) and its component nitric oxide (NO) have been made in the lower stratosphere. Box model. simulations that are constrained by observations of radical and longlived species and which include heterogeneous chemistry systematically underpredict the NO(x) (= NO + NO2) to NOY ratio. The model agreement is substantially improved if newly measured rate coefficients for the OH + NO2 and OH + HNO3 reactions are used. When included in 2-D models, the new rate coefficients significantly increase the calculated ozone loss due to NO(x) and modestly change the calculated ozone abundances in the lower stratosphere. Ozone changes associated with the emissions of a fleet of supersonic aircraft are also altered. phase chemistry linking NO(x) and nitric acid (HNO3), which is generally the most abundant NOY species. Because the continuous daylight present at summer high latitudes limits the heterogeneous production of HNO3 by N2O5 hydrolysis, gas-phase reactions primarily control the balance between NO(x) and NO(y). Outside summer polar regions, the N2O5 hydrolysis reaction occurring on stratospheric sulfate aerosols is a more important sink of NO(x), particularly in the lower stratosphere during winter when heterogeneous pathways account for most of the HNO3 production.

A comparison of modeled and measured surface shortwave irradiance for a molecular atmosphere

Abstract: We compare the downward diffuse and direct normal irradiance computed by a two-stream model with measurements taken at the Mauna Loa Observatory when the atmosphere was close to a molecular atmosphere. The modeled downward diffuse irradiance agrees with measurements taken by a shaded pyranometer within the uncertainty of the measurement. Therefore, the two-stream approximation is adequate for computing the downward diffuse irradiance in a molecular atmosphere. This result also indicates that neglecting the state of polarization introduces a negligible error in the irradiance computation.