Partitioning of Ozone Loss Pathways in the Ozone Quasi-biennial Oscillation Simulated by a Chemistry-Climate Model

Ozone loss pathways and their rates in the ozone quasi-biennial oscillation (QBO), which is simulated by a chemistry-climate model developed by the Meteorological Research Institute of Japan, are evaluated using an ob- jective pathway analysis program (PAP). The analyzed chemical system contains catalytic cycles caused by NOx , HOx , ClOx , Ox , and BrOx . PAP quantified the rates of all significant catalytic ozone loss cycles, and evaluated the partitioning among these cycles. The QBO amplitude of the sum of all cycles amounts to about 4 and 14 % of the annual mean of the total ozone loss rate at 10 and 20 hPa, respectively. The contribution of catalytic cycles to the QBO of the ozone loss rate is found to be as follows: NOx cycles contribute the largest fraction (50 – 85 %) of the QBO amplitude of the total ozone loss rate; HOx cycles are the second-largest (20 – 30 %) below 30 hPa and the third-largest (about 10 %) above 20 hPa; Ox cycles rank third (5 – 20 %) below 30 hPa and second (about 20 %) above 20 hPa; ClOx cycles rank fourth (5 – 10 %); and BrOx cycles are almost negligible. The relative contribution of the NOx and Ox cycles to the QBO amplitude of ozone loss differs by up to 10 % and 20 %, respectively, from their contribution to the annual mean ozone loss rate. The ozone QBO at 20 hPa is mainly driven by ozone transport, which then alters the ozone loss rate. In contrast, the ozone QBO at 10 hPa is driven chemically by NOx and the temperature dependence of [O]/[O3], which results from the temperature dependence of the reaction O + O2 + M → O3 + M. In addition, the ozone QBO at 10 hPa is influenced by the overhead ozone column, which affects [O]/[O3] (through ozone photolysis) and the ozone production rate (through oxygen photolysis)

Solar impact on the lower mesospheric subtropical jet: A comparative study with general circulation model simulations

The seasonal and interannual variation in the lower mesospheric subtropical jet (LMSJ) and their dependence on the 11-year solar cycle are studied by comparing observational data with simulations by two general circulation models. In the model simulations, a strengthening of the LMSJs is found in both hemispheres during the winter under the solar maximum condition, similar to the observation. However the model responses are substantially smaller except for one case in the southern hemisphere. It is also found that the stronger LMSJ due to an enhanced solar forcing appears during the period which follows an increasing period of interannual variation. Analysis of the observed seasonal march of the LMSJ in each year shows two different regimes of behavior. For a successful simulation, the model should realistically reproduce the observed interannual variability as well as the climatological mean

Apparent stratospheric ozone loss rate over Eureka in 1994/95, 1995/96, and 1996/97 inferred from ECC ozonesonde observations

Many ECC-type ozonesondes were launched at the Canadian Arctic Eureka observatory(80°N , 86°W ), one of the most northern stations in the Arctic, during winters from 1993/94 to 2001/02, and the temporal evolutions of the vertical ozone profiles were obtained in detail. The lower stratospheric temperature over Eureka was very low inside the polar vortex and the largest ozone loss was observed in 1999/2000, as reported in a previous paper. Similarly, Eureka was often or persistently inside the vortex in the lower stratosphere(around the 470K isentropic surface level) in the winters of 1994/95, 1995/96, and 1996/97. Very low temperatures were observed inside the vortex in the lower stratosphere over Eureka, as indicated by detection of PSCs by Mie lidar. Observations of tracers(N_2O, total reactive nitrogen species(NOy), and others) inside the vortex during these winters using an ER-2 aircraft and balloons indicated that the effect of air parcel mixing across the vortex edge was minimal, based on the tracer-tracer relationship(e.g., Y. Kondo et al.; J. Geophys. Res., 104D, 8215, 1999). Therefore, significant decreases of the in-travortex ozone mixing ratio in the lower stratosphere were considered to be chemical ozone losses due to chlorine activation of PSCs following diabatic descent. The apparent ozone loss rate inside the vortex over Eureka was estimated for each year. The rates ranged from 0.01 to 0.03ppmv/day, less than that observed in 1999/2000(0.04ppmv/day). The observations were conducted at a single station; however, the apparent ozone loss rate over Eureka inside the vortex each year agrees with loss rates obtained in other studies

On the representation of major stratospheric warmings in reanalyses

Major sudden stratospheric warmings (SSWs) represent one of the most abrupt phenomena of the boreal wintertime stratospheric variability, and constitute the clearest example of coupling between the stratosphere and the troposphere. A good representation of SSWs in climate models is required to reduce their biases and uncertainties in future projections of stratospheric variability. The ability of models to reproduce these phenomena is usually assessed with just one reanalysis. However, the number of reanalyses has increased in the last decade and their own biases may affect the model evaluation. Here we compare the representation of the main aspects of SSWs across reanalyses. The examination of their main characteristics in the pre- and post-satellite periods reveals that reanalyses behave very similarly in both periods. However, discrepancies are larger in the pre-satellite period compared to afterwards, particularly for the NCEP-NCAR reanalysis. All datasets reproduce similarly the specific features of wavenumber-1 and wavenumber-2 SSWs. A good agreement among reanalyses is also found for triggering mechanisms, tropospheric precursors, and surface response. In particular, differences in blocking precursor activity of SSWs across reanalyses are much smaller than between blocking definitions

Evidence for changes in stratospheric transport and mixing over the past three decades based on multiple data sets and tropical leaky pipe analysis

Variability in the strength of the stratospheric Lagrangian mean meridional or Brewer-Dobson circulation and horizontal mixing into the tropics over the past three decades are examined using observations of stratospheric mean age of air and ozone. We use a simple representation of the stratosphere, the tropical leaky pipe (TLP) model, guided by mean meridional circulation and horizontal mixing changes in several reanalyses data sets and chemistry climate model (CCM) simulations, to help elucidate reasons for the observed changes in stratospheric mean age and ozone. We find that the TLP model is able to accurately simulate multiyear variability in ozone following recent major volcanic eruptions and the early 2000s sea surface temperature changes, as well as the lasting impact on mean age of relatively short-term circulation perturbations. We also find that the best quantitative agreement with the observed mean age and ozone trends over the past three decades is found assuming a small strengthening of the mean circulation in the lower stratosphere, a moderate weakening of the mean circulation in the middle and upper stratosphere, and a moderate increase in the horizontal mixing into the tropics. The mean age trends are strongly sensitive to trends in the horizontal mixing into the tropics, and the uncertainty in the mixing trends causes uncertainty in the mean circulation trends. Comparisons of the mean circulation and mixing changes suggested by the measurements with those from a recent suite of CCM runs reveal significant differences that may have important implications on the accurate simulation of future stratospheric climate

Meiosis-Specific Loading of the Centromere-Specific Histone CENH3 in Arabidopsis thaliana

Centromere behavior is specialized in meiosis I, so that sister chromatids of homologous chromosomes are pulled toward the same side of the spindle (through kinetochore mono-orientation) and chromosome number is reduced. Factors required for mono-orientation have been identified in yeast. However, comparatively little is known about how meiotic centromere behavior is specialized in animals and plants that typically have large tandem repeat centromeres. Kinetochores are nucleated by the centromere-specific histone CENH3. Unlike conventional histone H3s, CENH3 is rapidly evolving, particularly in its N-terminal tail domain. Here we describe chimeric variants of CENH3 with alterations in the N-terminal tail that are specifically defective in meiosis. Arabidopsis thaliana cenh3 mutants expressing a GFP-tagged chimeric protein containing the H3 N-terminal tail and the CENH3 C-terminus (termed GFP-tailswap) are sterile because of random meiotic chromosome segregation. These defects result from the specific depletion of GFP-tailswap protein from meiotic kinetochores, which contrasts with its normal localization in mitotic cells. Loss of the GFP-tailswap CENH3 variant in meiosis affects recruitment of the essential kinetochore protein MIS12. Our findings suggest that CENH3 loading dynamics might be regulated differently in mitosis and meiosis. As further support for our hypothesis, we show that GFP-tailswap protein is recruited back to centromeres in a subset of pollen grains in GFP-tailswap once they resume haploid mitosis. Meiotic recruitment of the GFP-tailswap CENH3 variant is not restored by removal of the meiosis-specific cohesin subunit REC8. Our results reveal the existence of a specialized loading pathway for CENH3 during meiosis that is likely to involve the hypervariable N-terminal tail. Meiosis-specific CENH3 dynamics may play a role in modulating meiotic centromere behavior

Studies of the Effect of Seasonal Cycle on the Equatorial Quasi-Biennial Oscillation with a Chemistry-Climate Model

The effect of the seasonal cycle on the quasi-biennial oscillation (QBO) in the equatorial stratosphere was investigated using a chemistry-climate model (CCM) by fixing the seasonal cycle in CCM simulations. The CCM realistically reproduced the QBO in wind and ozone fields of a 30-month period in a climatological simulation (control run) under annually repeating sea surface temperature (SST) with a seasonal cycle. For the control run, four experimental simulations (perpetual runs) were made by fixing solar declination and SST on the 15th of January, April, July, and October, respectively, for about 20 years. In the three perpetual runs of January, July, and October, the QBO was maintained and persisted throughout the 20-year integration in spite of some small differences in period and amplitude among the three runs. On the other hand, the QBO in the perpetual April run began to weaken after about 15 years and the downward propagation of westerly wind stopped at about 20 hPa, resulting in the QBO’s ceasing. The cause of this QBO disappearance is related to the evolution of the background mean flow in the lower stratosphere, which filtered out the parameterized gravity waves propagating upwards farther