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Papers by John Stanford

Journal of Geophysical Research: Atmospheres, 2000

High-resolution (-40 km) along-track total column ozone data from the Total Ozone Mapping Spectro... more High-resolution (-40 km) along-track total column ozone data from the Total Ozone Mapping Spectrometer (TOMS) instrument are compared with a high-resolution mesoscale numerical model analysis of an intense cyclone in the Midwestern United States. Total ozone increased by-100 DU (nearly 38%) as the TOMS instrument passed over the associated tropopause fold region. Complex structure is seen in the meteorological fields and compares well with the total ozone observations. Ozone data support the meteorological analysis showing that stratospheric descent was confined to levels above-600 hPa; significant positive potential vorticity at lower levels is attributable to diabatic processes. Likewise, meteorological fields show that two pronounced ozone streamers extending north and northeastward into Canada at high levels are not bands of stratospheric air feeding into the cyclone; one is a channel of exhaust downstream from the system, and the other apparently previously connected the main cyclonic circulation to a southward intrusion of polar stratospheric air and advected eastward as the cutoff cyclone evolved. Good agreement between small-scale features in the model output and total ozone data underscores the latter's potential usefulness in diagnosing uppertropospheric/lower-stratospheric dynamics and kinematics. 00 PI/=-grlo Op ' (1) where r/0 is the absolute vorticity evaluated on an isentropic surface. Potential vorticity is a function of the atmospheric static stability, and the stratosphere is therefore a reservoir of high values of PV. Anomalously large values of PV found at

Journal of the American Statistical Association, 1995

Journal of the Atmospheric Sciences, 1984

Geophysical Research Letters, 1993

Randel [1992] has recently reported evidence for Rossby-gravity waves in tropical data fields pro... more Randel [1992] has recently reported evidence for Rossby-gravity waves in tropical data fields produced by the European Centre for Medium Range Weather Forecasts (ECMWF). The purpose of this paper is to show that similar features are observable in fields of total column ozone from the Total Ozone Mapping Spectrometer (TOMS) satellite instrument. The observed features are episodic, have zonal (east-west) wavelengths of-,• 6,000-10,000 km and oscillate with periods of 5-10 days. The modes exhibit westward phase progression and eastward group velocity. A simple linear model is used to' estimate the magnitude of total ozone perturbations induced by Rossby-gravity waves. The model is able to account for the magnitude of observed TOMS features as well as their asymmetry about the equator. The significance of finding Rossby-gravity waves in total ozone fields is that (1) the report of similar features in ECMWF tropical fields is corroborated with an independent data set and (2) the TOMS data set is demonstrated to possess surprising versatility and sensitivity to relatively smaller scale tropical phenomena.

Journal of the Atmospheric Sciences

Journal of the Atmospheric Sciences, 1991

Journal of the Atmospheric Sciences, 1989

ABSTRACT The stability of basic states consisting of a jet similar to the stratospheric polar nig... more ABSTRACT The stability of basic states consisting of a jet similar to the stratospheric polar night jet and a traveling wave with a single zonal wavenumber is examined in a linearized nondivergent barotropic model on a sphere. Basic state waves are chosen to resemble observed traveling and stationary features in the winter stratosphere. Results are presented for disturbance growth rates, propagation characteristics, and energy conversion as a function of the basic state wave amplitude. The effects of small amplitude basic state waves on unstable disturbances arising from a zonally symmetric jet are discussed; results are shown where a small amplitude basic state wave dramatically affects the stability characteristics. Evidence is shown that the presence of a traveling wave may favor the appearance of disturbances that include other zonal wavenumbers which move with the basic state wave; this result is discussed in relation to the origin of observed quasi-nondispersive features in the polar winter stratosphere. Results for a stationary wavenumber 1 basic state wave suggest that a distorted polar vortex may be unstable to disturbances that would lead to further distortion. An unstable disturbance for a basic state with an eastward moving wavenumber 2 has components which resemble, in period and location, traveling waves that are observed in the winter stratosphere.

Journal of the Atmospheric Sciences, 1999

Structure and kinematics of carbon monoxide in the upper stratosphere and lower mesosphere (10-0.... more Structure and kinematics of carbon monoxide in the upper stratosphere and lower mesosphere (10-0.03 hPa) are studied for the early northern winter 1991/92 using the Upper Atmosphere Research Satellite Improved Stratospheric and Mesospheric Sounder (ISAMS) measurements. The study is aided by data from a 6-week parameterized-chemistry run of the Goddard Space Flight Center 3D Chemistry and Transport Model (CTM), initialized on 8 December 1991. Generally, CO mixing ratios increase with height due to the increasing source contribution from CO 2 photolysis. In the tropical upper stratosphere, however, a local maximum in CO mixing ratio occurs. A simple photochemical model is used to show that this feature results largely from methane oxidation. In the extratropics the photochemical lifetime of CO is long, and therefore its evolution is dictated by largescale motion of air, evidenced by strong correlation with Ertel potential vorticity. This makes CO one of the few useful observable tracers at the stratopause level and above. Thus CO maps are used to study the synoptic evolution of the polar vortex in early January 1992. Modified Lagrangian mean mixing diagnostics are applied to ISAMS and CTM data to examine the strength of the mixing barrier at the polar vortex edge. It is demonstrated that planetary wave activity weakens the barrier, promoting vortex erosion. The vortex erosion first appears in the lower mesosphere and subsequently descends through the upper stratosphere, and is attributed to effects of planetary wave dissipation. Agreement between ISAMS and CTM is good in the horizontal distribution of CO throughout the examined period, but vertical CO gradients in the CTM weaken with time relative to the ISAMS observations.

Journal of Geophysical Research, 1994

Journal of Applied Physics, 1970

Journal of Applied Physics, 1969

Geophysical Research Letters, 2000

Antarctic polar descent and planetary wave activity in the upper stratosphere and lower mesospher... more Antarctic polar descent and planetary wave activity in the upper stratosphere and lower mesosphere are observed in ISAMS CO data from April to July 1992. COderived mean April-to-May upper stratosphere descent rates of 15 K/day (0.25 km/day) at 60 • S and 20 K/day (0.33 km/day) at 80 • S are compared with descent rates from diabatic trajectory analyses. At 60 • S there is excellent agreement, while at 80 • S the trajectory-derived descent is significantly larger in early April. Zonal wavenumber 1 enhancement of CO is observed on 9 and 28 May, coincident with enhanced wave 1 in UKMO geopotential height. The 9 May event extends from 40 to 70 km and shows westward phase tilt with height, while the 28 May event extends from 40 to 50 km and shows virtually no phase tilt with height.

Quart J Roy Meteorol Soc, 1987

Geophys Res Lett, 1991

Upper stratospheric photochemical lifetimes are estimated in situ for CH4 and N20 for the first t... more Upper stratospheric photochemical lifetimes are estimated in situ for CH4 and N20 for the first time, based on an analysis technique using 3 years of satellite measurements from the Stratospheric And Mesospheric Sounder (SAMS) instrument. The technique involves investigation of the time dependence of tracers injected into high Northern latitudes in late winter and their subsequent photochemical decay during the dynamically quiescent summer stratosphere. Dynamical corrections are made for mean meridional circulation contributions. The lifetimes for N20 at 2 and 7 hPa (~ 43 and ~ 35 km altitude) are found to be 1.7 and 8.3 months, respectively. For CHs, 0.6 (~ 52 km altitude) and 2 hPa lifetimes are 3.3 and 3.4 months, respectively. These observed values are in good agreement with model calculations by Solomon et

Geophysical Research Letters, 1991

Journal of the Atmospheric Sciences, 1987