Joseph L. Sabutis

Development of the polar vortex in the 1999–2000 Arctic winter stratosphere

The 1999–2000 Arctic stratospheric vortex was unusually cold, especially in the early winter lower stratosphere, with a larger area near polar stratospheric cloud formation temperatures in Dec and Jan, and much lower temperatures averaged over Nov–Jan, than any previously observed Arctic winter. In Nov and early Dec, there was a double jet in the upper stratosphere, with the anticyclone cutoff in a region of cyclonic material. By late Dec, there was a discontinuous vortex, large in the upper stratosphere, small in the lower stratosphere; evolving to a strong, continuous, relatively upright vortex by mid-Jan. This vortex evolution in 1999–2000 is typical of that in other cold early winters. Despite unusually low temperatures, the lower stratospheric vortex developed more slowly than in previous unusually cold early winters, and was weaker than average until late Dec.

Simulations of Dynamics and Transport during the September 2002 Antarctic Major Warming

Abstract A mechanistic model simulation initialized on 14 September 2002, forced by 100-hPa geopotential heights from Met Office analyses, reproduced the dynamical features of the 2002 Antarctic major warming. The vortex split on ∼25 September; recovery after the warming, westward and equatorward tilting vortices, and strong baroclinic zones in temperature associated with a dipole pattern of upward and downward vertical velocities were all captured in the simulation. Model results and analyses show a pattern of strong upward wave propagation throughout the warming, with zonal wind deceleration throughout the stratosphere at high latitudes before the vortex split, continuing in the middle and upper stratosphere and spreading to lower latitudes after the split. Three-dimensional Eliassen–Palm fluxes show the largest upward and poleward wave propagation in the 0°–90°E sector prior to the vortex split (coincident with the location of strongest cyclogenesis at the model’s lower boundary), with an additional re...

Diagnostic Comparison of Meteorological Analyses during the 2002 Antarctic Winter

Abstract Several meteorological datasets, including U.K. Met Office (MetO), European Centre for Medium-Range Weather Forecasts (ECMWF), National Centers for Environmental Prediction (NCEP), and NASA’s Goddard Earth Observation System (GEOS-4) analyses, are being used in studies of the 2002 Southern Hemisphere (SH) stratospheric winter and Antarctic major warming. Diagnostics are compared to assess how these studies may be affected by the meteorological data used. While the overall structure and evolution of temperatures, winds, and wave diagnostics in the different analyses provide a consistent picture of the large-scale dynamics of the SH 2002 winter, several significant differences may affect detailed studies. The NCEP–NCAR reanalysis (REAN) and NCEP–Department of Energy (DOE) reanalysis-2 (REAN-2) datasets are not recommended for detailed studies, especially those related to polar processing, because of lower-stratospheric temperature biases that result in underestimates of polar processing potential, ...

Wave propagation in the 1999–2000 Arctic early winter stratosphere

Stratospheric wave propagation during the unusually cold NH early winter 99–00 is studied and compared to the recent cold winters of 94–95, 95–96 (the previous coldest NH winter) and 96–97. EP fluxes reveal less wave activity entered the stratosphere in 95–96 and 99–00, substantial temperature decreases during long periods of little wave activity in 94–95 and 99–00, and little wave propagation into the upper stratosphere in Nov 99–Jan 00 and Nov 95–mid-Jan 96. 2-D and 3-D EP fluxes for 95–96 and 99–00 show both that wave activity was inhibited from propagating upward and poleward through the middle stratosphere until mid–Jan, and there was large horizontal propagation of wave activity in the middle and lower stratosphere during Nov and Dec. Thus, both less wave activity entering the stratosphere, and a background structure that prevented wave activity from propagating into the upper stratosphere, were important factors in producing unusually cold early winters in 95–96 and 99–00.

A unique stratospheric warming event in November 2000

Stratospheric sudden warmings frequently influence temperatures and circulation in the Arctic winter stratosphere. A unique stratospheric warming in Nov 2000 was characterized by wave 1 amplification with little phase tilt with height, a large displacement of the vortex off the pole, a warm pool at high latitudes, and a modest polar temperature increase, all of which are characteristic of early winter “Canadian” warmings. Unlike most Canadian warmings, the Nov 2000 event led to a strong zonal mean wind reversal for ∼9 days in the mid and lower stratosphere. Wind reversals during Canadian warmings occurred only three times before in the last 23 years. Midstratospheric minimum temperatures continued to decrease during the warming, but lower stratospheric temperatures increased substantially. The Nov 2000 warming was unique in its timing, intensity and duration, and in its impact on the development of the polar vortex, especially in the lower stratosphere.

The Short-Term Transport of Zonal Mean Ozone Using a Residual Mean Circulation Calculated from Observations

Abstract A transformed Eulerian mean residual circulation for the middle atmosphere is calculated from daily Limb Infrared Monitor of the Stratosphere data for the period 15 January 1979 to 10 February 1979. When compared to time-averaged results, the daily calculated circulations are shown to reproduce better and provide a mechanistic explanation of the short-term changes in the zonal mean temperature and ozone in the high-latitude stratosphere.

The Choice of a Vertical Grid for a 2.5D Numerical Model of the Middle Atmosphere

Abstract The consequences of choosing an unstaggered grid (UG), Charney-Phillips-type grid (CPG), or Lorenz-type grid (LG) in the vertical for a 2.5D model are examined. Analytical solutions for the linearized and scaled eddy equations in spherical coordinates are compared to solutions obtained by finite-difference methods. Waves with vertical structure greater than six gridpoint intervals are reliably reproduced by the model using any of these three grids. Waves with vertical structure between four and six gridpoint intervals appear in the model with shorter vertical wavelengths using the UG and CPG, and with longer vertical wavelengths using the LG. Waves with vertical structure less than four gridpoint intervals will be evanescent using the UG and CPG. Waves with vertical structure less than four gridpoint intervals will be propagated vertically using the LG; however, waves unresolved by the LG will spuriously appear and will be vertically propagated with an apparent vertical wavelength of three gridpo...