V. A. Yudin

Transport Diagnostics of GCMs and Implications for 2D Chemistry-Transport Model of Troposphere and Stratosphere

Abstract The middle atmosphere version of NCAR Community Climate Model (MACCM2) and the GEOS-STRATAN data assimilation system (DAS) of NASA/GSFC have been used to generate a zonally averaged set of transport parameters (meridional circulation and resolved eddy mixing) for use in two-dimensional (2D) chemistry transport models (CTMs). This was done by performing 3D transport numerical experiments with two orthogonal tracers. Some transport diagnostics from the MACCM2 and DAS are compared with each other, and with other approaches and estimates of horizontal mixing (Kyy) obtained from satellite data and GCMs. Some differences in the derived Kyy values for these passive tracer experiments and using the potential vorticity (PV) methods are discussed, as well as the annual and interannual variations, and the interhemispherical asymmetries in Kyy structures. The set of 2D parameters obtained from the MACCM2 transport diagnostics has been used in a 2D CTM to simulate the distribution of CH4, N2O, O3, and the age...

TMTM simulations of tides: Comparison with UARS observations

This paper presents combined model-data interpretation of the High Resolution Doppler Imager (HRDI) and Wind Imaging Interferometer (WINDII) wind, temperature and airglow data using the tuned mechanistic tidal model (TMTM) approach, including calculation of the nighttime oxygen emission rates induced by the simulated tides. This is the first demonstration of the consistency of the tidal signatures in the HRDI/WINDII temperature, airglow and wind observations in the mesosphere and lower thermosphere (MLT). This analysis gives increased confidence in these UARS measurements and also in our TMTM methodology.

UARS PSC, ClONO2, HCl, and ClO measurements in early winter: Additional verification of the paradigm for chlorine activation

We present an example of observations within a single air mass of ClO, ClONO2, and HCl from the instruments on the UARS spacecraft. A three-dimensional chemistry-transport calculation for HCl is used to show that this air mass has been transported through regions cold enough for polar stratospheric cloud formation and chlorine activation through heterogeneous chemical reactions. These data, together with modeling of HCl with and without heterogeneous loss as a qualitative measure of polar processing, indicate directly the transformation of the reservoirs HCl and ClONO2 to reactive chlorine species.

Tidal influences on O2 atmospheric band dayglow: HRDI observations vs. model simulations

Atmospheric tides perturb the temperature, winds, density, and composition of the mesosphere and lower thermosphere (MLT) and therefore affect daytime O2 atmospheric band airglow. O2 atmospheric band dayglow measurements made by the High Resolution Doppler Imager (HRDI) show clear tidal signatures in equatorial emission rates during equinox, when diurnal tide amplitudes are large. During solstice the observed symmetric diurnal variation of dayglow indicates an emission process controlled by solar absorption. Observations are compared with modeled emissions based on an atmosphere perturbed with diurnal tides predicted by the Tuned Mechanistic Tidal Model (TMTM) for March 1993. Good data/model agreement indicates enhanced emissions result from tidal advection of atomic oxygen from the lower thermosphere. While tides modulate O2 nightglow by perturbing atomic oxygen recombination rates, the tidal signatures seen in O2 dayglow are due to increased production of ozone and O(¹D). These results provide further confirmation of the consistency of the HRDI daytime wind, temperature and airglow observations.

Parameterization of the convective transport in a two‐dimensional chemistry‐transport model and its validation with radon 222 and other tracer simulations

Deep cumulus convection is essential for understanding and modeling of the atmospheric composition, providing a mechanism by which short-lived species can be quickly transported from the planetary boundary layer to the upper troposphere. Because it is a small scale process, highly irregular in time and space, so far most of the scientific community has been skeptical about the legitimacy of zonally averaged representations of tracer convective transport in two-dimensional (2-D) models. To justify and validate such an approach, we derive our parameterization of zonally averaged convective transport from a 3-D model and then validate our 2-D results against the results from that 3-D model using radon 222 and other tracer simulations. We show, both analytically and by comparing 2-D and 3-D model results, that straightforward substitution of zonally averaged parameters into the equations of tracer convective transport produces large errors because the intensity of the convection and the tracer concentration in the updraft and in the environment can be strongly correlated. If such correlations are taken into account in the zonally averaged equations for convective transport, the agreement between 2-D and 3-D results can be significantly improved. We show that our 2-D model with monthly mean convective mass fluxes, properly zonally averaged, is capable of reproducing, with reasonable accuracy, the time series of 222Rn and other tracers obtained from the 3-D simulations. Our convective transport algorithm and input data are available via anonymous ftp.

A UARS study of lower stratospheric polar processing in the early stages of northern and southern winters

UARS data and results from a three-dimensional transport model have been used to compare and contrast the extent of the early stages of chemical processing by polar stratospheric clouds (PSCs) during the 1991–1993 northern and southern hemisphere winters of the Upper Atmosphere Research Satellite (UARS) mission. The modeled location and timing of regions of polar processing agree quite well with the UARS microwave limb sounder (MLS), cryogenic limb array etalon spectrometer (CLAES) and Halogen Occultation Experiment (HALOE) observations in that enhanced ClO concentrations are generally found in sunlit regions of polar-processed air and decreases of ClONO2 and HNO3 accompany low temperatures and high values of the aerosol extinctions inside the vortex. For these winters it is found that there is a period of about 2 weeks during the northern hemisphere early winter where sporadic polar processing takes place. After this a persistent processing region is seen inside the polar vortex, and the vortex fills with polar-processed air in a bit more than 2 weeks from the first persistent PSC occurrence. In the southern hemisphere, polar processing also fills the vortex in a bit over 2 weeks. Estimates of the spectral aerosol measure of the aerosol spectrum from CLAES observations illustrate that PSC particles are seen where cold temperatures occur inside the polar vortex and heterogeneous conversion of chlorine species on PSCs are expected.