Dynamical implications of seasonal and spatial variations in Titan's stratospheric composition

2008 ◽  
Vol 367 (1889) ◽  
pp. 697-711 ◽  
Author(s):  
Nicholas A Teanby ◽  
Patrick G.J Irwin ◽  
Remco de Kok ◽  
Conor A Nixon
Keyword(s):  
Polar Vortex ◽  
Spatial Variations ◽  
The South ◽  
Trace Species ◽  
Time Period ◽  
Circulation Cell ◽  
Seasonal And Spatial Variations ◽  
Infrared Spectrometer ◽  
Stratospheric Circulation ◽  
Stratospheric Composition

Titan's diverse inventory of photochemically produced gases can be used as tracers to probe atmospheric circulation. Since the arrival of the Cassini–Huygens mission in July 2004 it has been possible to map the seasonal and spatial variations of these compounds in great detail. Here, we use 3.5 years of data measured by the Cassini Composite InfraRed Spectrometer instrument to determine spatial and seasonal composition trends, thus providing clues to underlying atmospheric motions. Titan's North Pole (currently in winter) displays enrichment of trace species, implying subsidence is occurring there. This is consistent with the descending branch of a single south-to-north stratospheric circulation cell and a polar vortex. Lack of enrichment in the south over most of the observed time period argues against the presence of any secondary circulation cell in the Southern Polar stratosphere. However, a residual cap of enriched gas was observed over the South Pole early in the mission, which has since completely dissipated. This cap was most probably due to residual build-up from southern winter. These observations provide new and important constraints for models of atmospheric photochemistry and circulation.

Contribution of large bacteria to bacterial biomass in a deep freshwater lake (Lake Biwa, Japan)

2020 ◽  
Vol 85 ◽  
pp. 131-139
Author(s):  
S Shen ◽  
Y Shimizu
Keyword(s):  
Cell Volume ◽  
Bacterial Cell ◽  
Lake Biwa ◽  
Bacterial Biomass ◽  
Spatial Variations ◽  
Freshwater Lake ◽  
Heterotrophic Nanoflagellates ◽  
Bacterial Productivity ◽  
Transmission Electron ◽  
Seasonal And Spatial Variations

Despite the importance of bacterial cell volume in microbial ecology in aquatic environments, literature regarding the effects of seasonal and spatial variations on bacterial cell volume remains scarce. We used transmission electron microscopy to examine seasonal and spatial variations in bacterial cell size for 18 mo in 2 layers (epilimnion 0.5 m and hypolimnion 60 m) of Lake Biwa, Japan, a large and deep freshwater lake. During the stratified period, we found that the bacterial cell volume in the hypolimnion ranged from 0.017 to 0.12 µm3 (median), whereas that in the epilimnion was less variable (0.016 to 0.033 µm3, median) and much lower than that in the hypolimnion. Additionally, in the hypolimnion, cell volume during the stratified period was greater than that during the mixing period (up to 5.7-fold). These differences in cell volume resulted in comparable bacterial biomass in the hypolimnion and epilimnion, despite the fact that there was lower bacterial abundance in the hypolimnion than in the epilimnion. We also found that the biomass of larger bacteria, which are not likely to be grazed by heterotrophic nanoflagellates, increased in the hypolimnion during the stratified period. Our data suggest that estimation of carbon flux (e.g. bacterial productivity) needs to be interpreted cautiously when cell volume is used as a constant parametric value. In deep freshwater lakes, a difference in cell volume with seasonal and spatial variation may largely affect estimations.

scholarly journals Long-range transport of volcanic aerosol from the 2010 Merapi tropical eruption to Antarctica

2018 ◽  
Author(s):  
Xue Wu ◽  
Sabine Griessbach ◽  
Lars Hoffmann
Keyword(s):  
Long Range ◽  
Lower Stratosphere ◽  
Polar Vortex ◽  
Volcanic Eruptions ◽  
Long Range Transport ◽  
Volcanic Plume ◽  
Volcanic Aerosol ◽  
The South ◽  
Range Transport ◽  
The Antarctic

Abstract. Volcanic sulfate aerosol is an important source of sulfur for Antarctica where other local sources of sulfur are rare. Mid- and high latitude volcanic eruptions can directly influence the aerosol budget of the polar stratosphere. However, tropical eruptions can also enhance polar aerosol load following long-range transport. In the present work, we analyze the volcanic plume of a tropical eruption, Mount Merapi in October 2010, using the Lagrangian particle dispersion model Massive-Parallel Trajectory Calculations (MPTRAC), Atmospheric Infrared Sounder (AIRS) SO2 observations and Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) aerosol observations. We investigate the pathway and transport efficiency of the volcanic aerosol from the tropical tropopause layer (TTL) to the lower stratosphere over Antarctica. We first estimated the time- and height-resolved SO2 injection time series over Mount Merapi during the explosive eruption using the AIRS SO2 observations and a backward trajectory approach. Then the SO2 injections were tracked for up to 6 months using the MPTRAC model. The Lagrangian transport simulation of the volcanic plume was compared to MIPAS aerosol observations and showed good agreement. Both of the simulation and the observations presented in this study suggest that a significant amount of aerosols of the volcanic plume from the Merapi eruption was transported from the tropics to the south of 60 °S within one month after the eruption and even further to Antarctica in the following two months. This relatively fast meridional transport of volcanic aerosol was mainly driven by quasi-horizontal mixing from the TTL to the extratropical lower stratosphere, which was facilitated by the weakening of the subtropical jet during the seasonal transition from austral spring to summer and linked to the westerly phase of the quasi-biennial oscillation (QBO). When the plume went to southern high latitudes, the polar vortex was displaced from the south pole, so the volcanic plume was carried to the south pole without penetrating the polar vortex. Based on the model results, the most efficient pathway for the quasi-horizontal mixing was in between the isentropic surfaces of 360 and 430 K. Although only 4 % of the initial SO2 load was transported into the lower stratosphere south of 60 °S, the Merapi eruption contributed about 8800 tons of sulfur to the Antarctic lower stratosphere. This indicates that the long-range transport under favorable meteorological conditions enables tropical volcanic eruptions to be an important remote source of sulfur for the Antarctic stratosphere.

scholarly journals Multi-decadal Records of Stratospheric Composition and their Relationship to Stratospheric Circulation Change

2017 ◽  
Author(s):  
Anne R. Douglass ◽  
Susan E. Strahan ◽  
Luke D. Oman ◽  
Richard S. Stolarski
Keyword(s):  
Transport Model ◽  
Atmospheric Composition ◽  
Model Driven ◽  
Earth Observing System ◽  
Circulation Change ◽  
Decadal Scale ◽  
Stratospheric Circulation ◽  
Transport And Mixing ◽  
Stratospheric Composition ◽  
Modern Era

Abstract. Constituent evolution for 1990–2015 simulated using the Global Modeling Initiative Chemistry and Transport Model driven by meteorological fields from the Modern Era Retrospective analysis for Research and Applications Version 2 (MERRA-2) is compared with three sources of observations: ground based column measurements of HNO3 and HCl from two stations in the Network for Detection of Atmospheric Composition Change (NDACCC, ~ 1990–ongoing); profiles of CH4 from the HALogen Occultation Experiment (HALOE) on the Upper Atmosphere Research Satellite (UARS, 1992–2005); profiles of N2O from the Microwave Limb Sounder on the Earth Observing System satellite Aura (2015–ongoing). The differences between observed and simulated values are shown to be time dependent, with better agreement after ~2000 compared with the prior decade. Furthermore, the differences between observed and simulated HNO3 and HCl columns are shown to be correlated with each other, suggesting that issues with the simulated transport and mixing cause the differences during the 1990s and these issues are less important during the later years. Because the simulated fields are related to mean age in the lower stratosphere, we use these comparisons to evaluate the time dependence of mean age. We use these relationships to account for dynamical variability when determining decadal scale trends in constituents and mean age. The ongoing NDACC column observations provide critical information necessary to substantiate trends in mean age obtained using fields from MERRA-2 or any other reanalysis products.

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