Svetlana V. Petelina

Transport and evolution of the 2009 Australian Black Saturday bushfire smoke in the lower stratosphere observed by OSIRIS on Odin

[1]xa0We report the transport and evolution of the Victorian Black Saturday bushfire smoke plume in the lower stratosphere during the February–June 2009 period. Vertical profiles of limb-scattered spectral solar radiation measured by the Optical Spectrograph and Infrared Imager System (OSIRIS) instrument on the Odin satellite are used for this purpose. According to OSIRIS measurements, the main smoke material penetrated above the tropopause on 11 February 2009. It traveled westward and circled the globe in about 6 weeks from its first detection in the lower stratosphere, remaining in the tropical channel between 5°S and 25°S. The main plume gradually advected from ∼19 km in mid-February to ∼22 km in April, with a vertical extent varying from 2 to 6 km. The background radiances at corresponding altitudes and latitudes were subtracted from the plume-containing radiances to obtain net plume peak radiances. The latter parameter, governed by the number, size, and chemical composition of smoke particles, decreased by half every 19 days from 11 February until the end of April 2009. Pollution of the lower stratosphere at 18–22 km altitudes and 5°S–25°S latitudes, caused by the smoke plume dispersion, was up to 35% above the background. By mid-June 2009, OSIRIS radiances at these altitudes and latitudes had almost returned to their background levels.

Relationship between the summer mesopause and polar mesospheric cloud heights

[1]xa0Satellite data analyses indicate that variations of daily mean polar mesospheric cloud (PMC) height and mesopause height correlate on a range of intraseasonal time scales both short and long (i.e., ∼4 days to 2 months). The average of a multiyear analysis from OSIRIS/Odin, SNOE, AIM, and SABER/TIMED data sets in the polar regions north (south) of 65°N (°S) shows that on a daily basis the mean PMC height (max) is located 3.5 km ± 0.5 km below the mean mesopause height (mes) in both hemispheres throughout the season and for all years examined. The data show that the relationship persists over multiple PMC seasons. This is a robust result that has also been verified with thermodynamic equilibrium and microphysical modeling. Model results from a large number of ensemble simulations show that max remains ∼3.5 km below mes as long as the vertical average of the ambient temperature minus the frost point temperature difference over the supersaturated region is about -10 K or less for all the individual simulations. max is located less than 3.5 km below mes for warmer supersaturated region temperatures. The distance between the cloud and the mesopause heights (Zmes − Zmax or ΔZ) is controlled by the corresponding temperature structure in the supersaturated region. It is concluded that the variation of ΔZ is mostly driven by the variation of the temperature structure instead of the H2O mixing ratio magnitude or vertical distribution.

Temperature of mesospheric ice retrieved from the O-H stretch band

[1]xa0For the first time, the temperature of mesospheric ice particles is retrieved directly from ice infrared extinction spectra measured in the solar occultation regime. The position of ice O-H stretch band peak varies from 3230cm−1 at T = 120K to 3246cm−1 at T = 155K, which enables the retrieval of ice temperature by fitting a model spectrum to a measured one. The retrieved temperature is independent of cloud vertical and horizontal patchiness and has a random uncertainty of <12K. The retrieval is sensitive to chosen particle shape: cubes, hexagons and spheroids of certain forms give same result. Spheres and rectangular prisms (aspect ratio ≥2) change temperature by 3–4K. For nearly 400 ice spectra analyzed the retrieved temperature for cubes ranges from 120K to 150K with the distribution maximum centered at ∼135K. The standard temperature for same ice spectra retrieved from the gas phase differs considerably and sometimes reaches values of 200K and above.

Computer simulation study of rotational diffusion in polar liquids of different types

Rotational diffusion in liquid acetonitrile, dimethylsulphoxide (DMSO), water, and methanol is studied with molecular dynamics simulations. The effects of hydrogen bonding and local dipole-dipole correlations (Kirkwood g-factor) on the relationship between the single molecule and collective relaxation are examined. The first rank single molecule dipole moment autocorrelation functions (ACFs) are constructed in the molecule-fixed coordinate frame and the principal components of rotation diffusion tensor are reported. Higher rank orientational ACFs are computed. These ACFs, as a rule, are strongly nonexponential (at least not single exponential) at longer times and the decomposition of these functions into a series of single exponentials results in broad distributions of relaxation times, with the broadening being particularly prominent in the case of higher rank ACFs. The rank dependence of characteristic times calculated as weighted averages over the relaxation time distributions does not follow the pattern of small angle (Debye) diffusion model for all liquids studied in this work except methanol. In contradiction, the same rank dependence computed by direct integration of ACFs leads to good agreement with the Debye diffusion model in the case of acetonitrile, DMSO, and water (but not methanol). The linear-angular momentum cross correlation functions are also computed and the effect of rototranslational coupling on reorientaional relaxation at longer times (>1.0u2002ps) is found to be small.

Ice particle growth in the polar summer mesosphere: Formation time and equilibrium size

[1]xa0The growth kinetics for ice particles in the polar summer mesosphere is studied using the density of water vapor, temperature, and total ice volume simultaneously measured by the infrared Fourier Transform Spectrometer on the Atmospheric Chemistry Experiment (ACE-FTS) satellite. The results are based solely on the ACE-FTS retrievals, without using any adjustable parameters. The computed particle formation time is in the range between 2 hours at 150 K and 20 hours at 120 K, during which particles come to equilibrium with water vapor and reach the size of 20–70 nm. The growth rate varies from 0.2 nm/hour to 30 nm/hour in the temperature range analyzed. As it takes ice crystals only 20 minutes to grow by 10 nm at 150 K, the transition from optically subvisible to the visible size range can occur on a time scale of minutes. This could account for fast variations in PMC brightness observed recently.

Relation between mesospheric ice clouds, temperature, and water vapor determined from Odin/OSIRIS and TIMED/SABER data

[1]xa0Altitude, brightness, and occurrence rate of polar mesospheric clouds (PMCs) with respect to kinetic temperature, pressure, and water vapor volume mixing ratio (VMR) in the ice formation area are studied. Cloud and atmospheric parameters are measured by the Optical Spectrograph and Infrared Imager System and by the Sounding of the Atmosphere using Broadband Emission Radiometry satellite instruments, correspondingly. The analysis has been done for all northern and southern PMC seasons of 2002–2008 for both zonal averages and nearly simultaneous common volume measurements performed by two instruments. It has been found that PMC peak altitudes correlate well with mesopause altitudes, although the former experience lower seasonal variability. Mesopause temperatures anticorrelate with PMC occurrence rates and, in the Northern Hemisphere, show larger seasonal variability at high latitudes poleward of 75°N compared to 55°N–65°N. OSIRIS PMC brightness correlates with the vertical extent of the frost area and water vapor VMR below PMC (hydration effect) and anticorrelates with the mesopause temperature and water vapor VMR in the frost area (freeze-drying effect).

Temperature of mesospheric ice particles simultaneously retrieved from 850 cm−1 libration and 3200 cm−1 vibration band spectra measured by ACE-FTS

[1]xa0We report a new approach to the retrieval of ice particle temperature in the atmosphere from midinfrared remote sensing observations. Two different in physical nature spectral bands of water ice, the libration band near 850 cm−1 and O-H stretch band at 3200 cm−1, are used simultaneously. The use of both bands in the unified least squares fitting procedure enables one to enhance the stability of fitting, as well as to improve the reliability and accuracy of retrieved ice temperature values. A set of reference spectra for the least squares minimization is compiled from experimental temperature-dependent optical constants for water ice that are available in the literature. The method is applied to the observations made by the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) instrument on board the SCISAT-1 satellite. According to our results, a combination of the vibration (3200 cm−1) and rotation (850 cm−1) bands within a unified minimization procedure can significantly, by about 4K, reduce the upper estimate of the total uncertainty in the retrieved temperatures from 12 K down to 8 K. The average temperature of bright mesospheric ice clouds observed by ACE-FTS during July 2005 is found to be about 131K, in contrast to the value of 135K retrieved from the vibration band alone.