A new calculation of nitric oxide photolysis in the stratosphere, mesosphere, and lower thermosphere

Abstract

Photodissociation of nitric oxide in the middle and upper atmosphere is examined using a line-by-line approach to describe absorption in the NO 5 bands and 02 Schumann-Runge bands. The new analysis of 02 absorption results in greater transmission of ultraviolet radiation in the Schumann-Runge (5-0) band in comparison with previous studies, leading to increased rates for photolysis of nitric oxide in the 5(0-0) band. Reduced transmission in the 02 (9-0) and (10-0) Schumann-Runge bands produces smaller photolysis rates for the NO 5(1-0) band. Absorption in strong lines of the NO 5 bands is shown to make a nonnegligible contribution to atmospheric opacity at wavelengths which are important for NO photodissociation. Representative distributions of nitric oxide are used to quantify possible changes in the NO photolysis rate over the course of a solar cycle. As a result of changes in the NO abundance in the thermosphere, modulation of the photolysis frequency at lower altitudes may be opposite in phase to variations in the solar irradiance. For solar zenith angles greater than 60 ø, photolysis rates at altitudes below 100 km may be smaller during solar maximum compared to solar minimum. A method is described which enables rapid calculation of NO photolysis frequencies, allowing also for effects of varying opacity by nitric oxide. Reactions (1) and (2) represent a net loss of two NO molecules. This sink is the dominant loss process for N Oxin the upper stratosphere, mesosphere, and lower themnosphere. Early estimates of the photolysis frequency of nitric oxide, JNO, were made by Bates [1954], Strobet et at. [1970], and $trobet [1971], although the first quantitative calculation to explicitly account for the NO rotational line structure was that of Ciestik and Nicotet [1973]. They demonstrated that the dominant contribution was due to predissociation in the (0-0) and (1-0) delta bands (C-X). Weaker absorption, occurring primarily in the beta bands (B-X, v' > 6) and gamma bands (A-X, v' • 3), was expected to play a minor role in determining the overall photolysis frequency in the stratosphere and mesosphere. The magnitude of JNO at zero optical depth was estimated to be greater than I x 10 -5 s -•. It was then shown by Frederick and Hudson [1979a] (hereinafter referred to as FH79) that values for the oscilla-Paper number 93JD02007. 0148-0227 / 93 / 93 J D-0200 7505.00 for strengths used by Ciestik and Nicotet [1973] were likely to have been over a factor of 2 too large. FH79 calculated revised values of Jr•o which were later parameterized by Allen and Frederick [1982] in a form suitable for photochemical models. Nicolet and Ciestik [1980] (hereinafter referred to as NC80) also obtained reduced estimates of JNO using smaller values for the oscillator strengths. An analytic approximation of their results was presented by Nicolet [1979]. Finally, Frederick et al. [1983] showed that NO absorption in the thermosphere could provide sufficient opacity in the cores of strong lines to reduce the photolysis frequency in the strato...

The HAMMONIA Chemistry Climate Model: Sensitivity of the Mesopause Region to the 11-Year Solar Cycle and CO2 Doubling

“…The part of the spectrum ranging from 120 to 200 nm is treated explicitly with 34 wavelength intervals and uses parameterizations for the photolysis of O 2 from Chabrillat and Kockarts (1998; Lyman-␣), Brasseur and Solomon (1986; Schumann-Runge continuum), and Koppers and Murtagh (1996;SchumannRunge bands). The NO photolysis is treated according to Minschwaner and Siskind (1993).…”

Quantum interference in the Schumann‐Runge bands of molecular oxygen

“…There may be some impact, for example, on calculations of the NO photodissociation profile. Many of the strongest lines of the NO 5(1,0) band lie in the window between the (9,0) and (10,0) SR bands where the basal cross section is determined largely by the blue wing of the (9,0) band head [Minschwaner and Siskind, 1993]. The rotationless CSE cross section (Fig.…”

Solar signals in CMIP‐5 simulations: the ozone response

“…For wavelengths > 200 nm and at altitudes below 65 km, the heating rates are calculated using the scheme of Briegleb (1992), which is based on the two-stream deltaEddington approximation (see also Briegleb and Light 2007 The WACCM also includes photolysis rates in the SchumannRunge bands (Koppers and Murtaugh 1996;Minschwaner and Siskind 1993) and Lyman-α line (Chabrillat and Kockarts 1997).…”