Jack A. Kaye

HCN formation on Jupiter: The coupled photochemistry of ammonia and acetylene

Abstract A model is presented for the formation of HCN in the upper troposphere and lower stratosphere of Jupiter by ultraviolet photolysis of the C 2 H 5 N isomer aziridine, a product of the recombination of NH 2 and C 2 H 3 radicals, which originate, respectively, from ammonia photolysis and addition of H atoms to acetylene. An HCN column density of ∼ 2 × 10 17 cm −2 in the tropopause region, which is comparable to that observed by A. T. Tokunaga, S. C. Beck, T. R. Geballe, J. H. Lacy, and E. Serabyn ( Icarus 48 , 283–289, 1981), is predicted when vertical mixing is slow above the ammonia cloudtops. Sensitivity of the HCN column density to the individual rate constants and the eddy diffusion coefficient profile is discussed, as is the possibility of the existence of additional HCN-yielding pathways. Ammonia, which is saturated in the upper troposphere, is strongly depleted by photolysis in the lower stratosphere. Phosphine is also strongly depleted by photolysis and its abundance in the upper troposphere is shown to depend strongly on vertical mixing in the tropopause region. The possibility of the formation of phosphirane, the P-containing analog of aziridine, is considered but found to be substantially less probable than aziridine.

The use of assimilated stratospheric data in constituent transport calculations

Abstract Analysis of atmospheric data by assimilation of height and wind measurements into a general circulation model is routine in tropospheric analysis and numerical weather prediction. A stratospheric assimilation system has been developed at NASA/Goddard Space Flight Center. This unique system generates wind data that is consistent with the geopotential height (and temperature) field and the primitive equations in the general circulation model. These wind fields should offer a significant improvement over the geostrophic analysis normally used in the stratosphere. This paper reports the first known calculations to use data from an assimilation to calculate constituent transport in the stratosphere. Nitric acid (NHO3) during the LIMS period is studied. While there are still significant discrepancies between the calculated and observed HNO3, there are some remarkable successes. Particularly, the high-latitude time variance of the HNO3 is accurately captured. These studies suggest that data from an assi...

Episodic total ozone minima and associated effects on heterogeneous chemistry and lower stratospheric transport

A description of the January 31, 1989, ozone minihole over Stavanger, Norway, is given on the basis of three-dimensional model simulations. This minihole is typical (though of large magnitude) of many transient events in the lower stratosphere that arise because of cyclonic-scale disturbances in the troposphere. The ozone reduction is a short-lived reversible dynamical event. However, through heterogeneous chemical processes there can be a significant transfer of chlorine from reservoir molecules to active radicals. This chemically perturbed air is defined as processed air, and it is found that a single event can produce enough processed air to reduce the HCl in the entire polar vortex. Chemical processing on clouds associated with transient events is shown to be a major source of processed air in the polar vortex in December before background temperatures are cold enough for more uniform heterogeneous conversion. In the model, intense cyclonic scales propagating close to the vortex edge and large planetary wave events (especially stratospheric warmings) are the major mechanisms of extra-vortex transport. Only a small amount of processed air is found outside of the polar vortex. The processed air is a strong function of longitude, and it is virtually excluded from the Pacific Basin.

Three‐dimensional simulations of wintertime ozone variability in the lower stratosphere

The evolution of ozone has been calculated for the winters of 1979 and 1989 using winds derived from our stratospheric data assimilation system (STRATAN). The ozone fields calculated using this technique are found to compare well with satellite-measured fields for simulations of 2–3 months. Here we present comparisons of model fields with both satellite and sonde measurements to verify that stratospheric transport processes are properly represented by this modeling technique. Attention is focussed on the northern hemisphere middle and high latitudes at the 10-hPa level and below, where transport processes are most important to the ozone distribution. First-order quantities and derived budgets from both the model and satellite data are presented. By sampling the model with a limb-viewing satellite and then Kalman filtering the “observations” of the model, it is shown that transient subplanetary-scale features that are essential to the ozone budget are missed by the satellite system.

Phosphine photochemistry in the atmosphere of Saturn

A model is presented for the photochemistry of PH3 in the upper troposphere and lower stratosphere of Saturn that includes the effects of coupling with NH3 and hydrocarbon photochemistry, specifically the C2H2 catalyzed photodissociation of CH4. PH3 is rapidly depleted with altitude (scale height ∼35 km) in the upper troposphere when K∼104cm2sec−1; an upper limit for K at the tropopause is estimated at ∼105cm2sec−1. If there is no gas phase P2H4 because of sublimation, P2 and P4 formation is unlikely unless the rate of the spin-forbidden recombination reaction PH + H2 + M → PH3 + M is exceedingly slow. An upper limit P4 column density of ∼2×1015cm−2 is estimated in the limit of no recombination. If sublimation does not remove all gas phase P2H4, P2 and P4 may be produced in potentially larger quantities, although they would be restricted almost entirely to the lowest levels of our model, where T≳100°K. Potentially observable amounts of the organophosphorus compounds CH3P2H2 and HCP are predicted, with column densities of >1017 cm−2 and production rates of ∼2×108cm−2sec−1. The possible importance of electronically excited states of PHx and additional PH3/hydrocarbon photochemical coupling paths are also considered.

Nonlocal thermodynamic equilibrium effects in stratospheric NO and implications for infrared remote sensing

It is shown that the vibrational state population of stratospheric nitric oxide (NO) could be substantially different from that expected on the basis of local thermodynamic equilibrium (LTE). Deviations from LTE may arise because stratospheric NO can be photochemically produced from NO(2) with several vibrational quanta. Model calculations suggest that the population of NO(upsilon = l) could be some 30% above that expected from LTE at 30 km with smaller enhancements above and below. Substantially larger enhancements are predicted for NO(upsilon = 2). This result is shown to have important implications for NO determination by remote sensing of IR emission. Data needed for the quantification of these effects are enumerated.

The influlence of polar heterogeneous processes on reactive chlorine at middle latitudes: Three dimensional model implications

Three dimensional model calculations with the NASA/GSFC chemistry and transport model have been designed to consider the impact of heterogeneous processes occurring on polar stratospheric clouds (PSCs) in the Arctic vortex on the HCl distribution. By examining the HCl concentration for a calculation with PSCs relative to a calculation with gas phase chemistry only, the authors infer the impact of polar processing on reactive chlorine species at middle latitudes. Results from the chemistry and transport model reproduce basic features of the ClO measurements (Toohey et al., 1991), which were made on the ferry flights of the ER-2 from Stavanger, Norway to Moffett Field, California via Wallops Island, Virginia on February 20 and 21, 1989. The model indicates that perturbed air which is contained within the polar vortex during winter is not homogeneously mixed, and that the ferry flights were made through air with the largest conversion of HCl to reactive chlorine that is seen at middle latitudes.

Formation and photochemistry of Methylamine in Jupiter's atmosphere

Abstract The formation of methylamine (CH 3 NH 2 ) in the upper troposphere and lower stratosphere of Jupiter is investigated. Translationally hot hydrogen atoms are produced in the photolysis of ammonia, phosphine, and acetylene which react with methane to produce methyl (CH 3 ) radicals; the latter recombine with NH 2 to form CH 3 NH 2 . Also, methane is catalytically dissociated to CH 3 + H by the species C 2 and C 2 H produced in the photolysis of acetylene. It is shown that the combined production of CH 3 NH 2 and subsequent photolysis to HCN is unlikely to account for the HCN observed near Jupiters tropopause. Recombination of NH 2 and C 2 H 5 N followed by photolysis to HCN is the preferred path. Production of C 2 H 6 by these two processes is negligible in comparison to the downward flux of C 2 H 6 from the Lyman α photolysis region of CH 4 . An upper limit column density on CH 3 PH 2 is estimated to be ∼10 13 cm −2 as compared to 10 15 cm −2 for CH 3 NH 2 . Hot H atoms account for a negligible fraction of the total ortho-para conversion by the reaction H + H 2

Analysis of the origins and implications of the O-18 content of stratospheric water vapor

Factors influencing the18O content of stratospheric H2O are reviewed in order to provide a theoretical framework for the interpretation of measurements of this quantity, which are now becoming available. Depletions in18O of 5–10% in stratospheric H2O are expected based on the known correlation between that of D and18O in tropospheric H2O and observed measurements of large (typically 50%) depletions of D in stratospheric H2O. H2O formed in the stratosphere as a result of oxidation of CH4 can be expected to reflect primarily the18O content of stratospheric O2, which is the same as that of tropospheric O2 (slightly enhanced with respect to standard mean ocean water). Thus, a reduction in the18O depletion is expected with increasing altitude, but not a large enhancement in18O in upper stratospheric H2O as found in recent far infrared measurements. The observed large enhancement of18O in stratospheric O3 is not expected to be reflected in stratospheric H2O. Necessary laboratory data for the improved quantification of these effects are reviewed.

Spatial and temporal variability of the extent of chemically processed stratospheric air

Simulations of the spatial and temporal variability of the extent of chemically processed air in the Arctic stratosphere have been carried out using a three-dimensional chemistry-transport model for the winters of 1979 and 1989, Chemically processed air is identified in the model as that in which the amounts of hydrogen chloride (HCl) calculated with parameterized loss for conditions appropriate to polar stratospheric cloud (PSC) formation are substantially smaller than those calculated in a model with gas phase chemistry only. It is seen that chemically processed air may be identified over much of the Arctic lower stratosphere from early January to late February, with HCl depletions being larger in 1989 than in 1979. Near the latitude of the Arctic circle, there is important spatial and temporal variability in the extent of chemically processed air. There is some evidence for transport to mid-latitudes of processed air during these winters, but the HCl reductions are much smaller and more sporadic than those near the pole. At 62 and 42N, processed air is calculated to occur preferentially over the longitude regions from 60-120E and 270-330E.