scholarly journals A model study of ozone in the eastern Mediterranean free troposphere during MINOS (August 2001)

2003 ◽  
Vol 3 (4) ◽  
pp. 1199-1210 ◽  
Author(s):  
G. J. Roelofs ◽  
H. A. Scheeren ◽  
J. Heland ◽  
H. Ziereis ◽  
J. Lelieveld
Keyword(s):  
North America ◽  
East Asia ◽  
Tropospheric Ozone ◽  
Eastern Mediterranean ◽  
Eastern Mediterranean Region ◽  
Lower Troposphere ◽  
Tropospheric Chemistry ◽  
The Tibetan Plateau ◽  
South East Asia ◽  
European Continent

Abstract. A coupled tropospheric chemistry-climate model is used to analyze tropospheric ozone distributions observed during the MINOS campaign in the eastern Mediterranean region (August, 2001). Modeled ozone profiles are generally in good agreement with the observations. Our analysis shows that the atmospheric dynamics in the region are strongly influenced by the occurrence of an upper tropospheric anti-cyclone, associated with the Asian summer monsoon and centered over the Tibetan Plateau. The anti-cyclone affects the chemical composition of the upper troposphere, where ozone concentrations of about 50 ppbv were measured, through advection of boundary layer air from South-East Asia. A layer between 4-6 km thickness was present beneath, containing up to 120 ppbv of ozone with substantial contributions by transport from the stratosphere and through lightning NOx. Additionally, pollutant ozone from North America was mixed in. Ozone in the lower troposphere originated mainly from the European continent. The stratospheric influence may be overestimated due to too strong vertical diffusion associated with the relatively coarse vertical resolution. The estimated tropospheric ozone column over the eastern Mediterranean is ~50 DU in summer, to which ozone from recent stratospheric origin contributes about 30%, ozone from lightning 13%, and from South-East Asia, North America and Europe about 7%, 8% and 14%, respectively, adding to a long-term hemispheric background of 25% of the column.

scholarly journals Distribution and origin of ozone in the eastern Mediterranean free troposphere during MINOS (August 2001)

2003 ◽  
Vol 3 (2) ◽  
pp. 1247-1272 ◽  
Author(s):  
G.-J. Roelofs ◽  
B. Scheeren ◽  
J. Heland ◽  
H. Ziereis ◽  
J. Lelieveld
Keyword(s):  
North America ◽  
East Asia ◽  
Tropospheric Ozone ◽  
Eastern Mediterranean ◽  
Eastern Mediterranean Region ◽  
Lower Troposphere ◽  
Tropospheric Chemistry ◽  
The Tibetan Plateau ◽  
South East Asia ◽  
European Continent

Abstract. A coupled tropospheric chemistry – climate model is used to reproduce and analyze tropospheric ozone distributions observed during the MINOS campaign in the eastern Mediterranean region (August, 2001). Generally, regional atmospheric dynamics in summer are strongly influenced by the occurrence of an upper tropospheric anti-cyclone, associated with the Asian summer monsoon and centered over the Tibetan Plateau. The anti-cyclone affects the chemical composition of the upper troposphere, where ozone concentrations of about 50 ppbv were measured, through advection of boundary layer air from South-East Asia. A layer between 4–6 km thickness and containing up to 120 ppbv of ozone was present beneath. Ozone from stratospheric origin and from lightning NOx contributed to this layer. Additionally, pollutant ozone from North America was mixed in. Ozone in the lower troposphere originated mainly from the European continent. Modeled ozone profiles are in reasonable agreement with the observations. The stratospheric influence is sometimes overestimated by the model due to too strong vertical diffusion associated with the relatively coarse vertical resolution of the model, and specific convective events are not reproduced realistically. The modeled tropospheric ozone column over the eastern Mediterranean is ~50 DU in summer, to which ozone from recent stratospheric origin contributes about 30%, ozone from lightning 13%, and from South-East Asia, North America and Europe about 7%, 8% and 14%, respectively, adding to a long-term hemispheric background of 25% of the column.

scholarly journals On the impact of future climate change on tropopause folds and tropospheric ozone

2019 ◽  
Vol 19 (22) ◽  
pp. 14387-14401 ◽  
Author(s):  
Dimitris Akritidis ◽  
Andrea Pozzer ◽  
Prodromos Zanis
Keyword(s):  
Atmospheric Chemistry ◽  
Tropospheric Ozone ◽  
Eastern Mediterranean ◽  
Stratospheric Ozone ◽  
Lower Troposphere ◽  
Future Climate Change ◽  
Identification Algorithm ◽  
The Future ◽  
Projected Changes ◽  
The Impact

Abstract. Using a transient simulation for the period 1960–2100 with the state-of-the-art ECHAM5/MESSy Atmospheric Chemistry (EMAC) global model and a tropopause fold identification algorithm, we explore the future projected changes in tropopause folds, stratosphere-to-troposphere transport (STT) of ozone, and tropospheric ozone under the RCP6.0 scenario. Statistically significant changes in tropopause fold frequencies from 1970–1999 to 2070–2099 are identified in both hemispheres, regionally exceeding 3 %, and are associated with the projected changes in the position and intensity of the subtropical jet streams. A strengthening of ozone STT is projected for the future in both hemispheres, with an induced increase in transported stratospheric ozone tracer throughout the whole troposphere, reaching up to 10 nmol mol−1 in the upper troposphere, 8 nmol mol−1 in the middle troposphere, and 3 nmol mol−1 near the surface. Notably, the regions exhibiting the largest changes of ozone STT at 400 hPa coincide with those with the highest fold frequency changes, highlighting the role of the tropopause folding mechanism in STT processes under a changing climate. For both the eastern Mediterranean and Middle East (EMME) and Afghanistan (AFG) regions, which are known as hotspots of fold activity and ozone STT during the summer period, the year-to-year variability of middle-tropospheric ozone with stratospheric origin is largely explained by the short-term variations in ozone at 150 hPa and tropopause fold frequency. Finally, ozone in the lower troposphere is projected to decrease under the RCP6.0 scenario during MAM (March, April, and May) and JJA (June, July, and August) in the Northern Hemisphere and during DJF (December, January, and February) in the Southern Hemisphere, due to the decline of ozone precursor emissions and the enhanced ozone loss from higher water vapour abundances, while in the rest of the troposphere ozone shows a remarkable increase owing mainly to the STT strengthening and the stratospheric ozone recovery.

The Influence of Mechanical and Thermal Forcing by the Tibetan Plateau on Asian Climate

2007 ◽  
Vol 8 (4) ◽  
pp. 770-789 ◽  
Author(s):  
Guoxiong Wu ◽  
Yimin Liu ◽  
Qiong Zhang ◽  
Anmin Duan ◽  
Tongmei Wang ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
East Asia ◽  
South China ◽  
Local Heating ◽  
Lower Troposphere ◽  
Early Spring ◽  
The Tibetan Plateau ◽  
Continental Scale ◽  
The North ◽  
Meridional Winds

Abstract This paper attempts to provide some new understanding of the mechanical as well as thermal effects of the Tibetan Plateau (TP) on the circulation and climate in Asia through diagnosis and numerical experiments. The air column over the TP descends in winter and ascends in summer and regulates the surface Asian monsoon flow. Sensible heating on the sloping lateral surfaces appears from the authors’ experiments to be the major driving source. The retarding and deflecting effects of the TP in winter generate an asymmetric dipole zonal-deviation circulation, with a large anticyclone gyre to the north and a cyclonic gyre to the south. Such a dipole deviation circulation enhances the cold outbreaks from the north over East Asia, results in a dry climate in south Asia and a moist climate over the Indochina peninsula and south China, and forms the persistent rainfall in early spring (PRES) in south China. In summer the TP heating generates a cyclonic spiral zonal-deviation circulation in the lower troposphere, which converges toward and rises over the TP. It is shown that because the TP is located east of the Eurasian continent, in summertime the meridional winds and vertical motions forced by the Eurasian continental-scale heating and the TP local heating are in phase over the eastern and central parts of the continent. The monsoon in East Asia and the dry climate in middle Asia are therefore intensified.

scholarly journals MAX-DOAS measurements of NO<sub>2</sub>, SO<sub>2</sub>, HCHO, and BrO at the Mt. Waliguan WMO GAW global baseline station in the Tibetan Plateau

2020 ◽  
Vol 20 (11) ◽  
pp. 6973-6990 ◽  
Author(s):  
Jianzhong Ma ◽  
Steffen Dörner ◽  
Sebastian Donner ◽  
Junli Jin ◽  
Siyang Cheng ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Trace Gases ◽  
Elevation Angle ◽  
Lower Troposphere ◽  
Statistical Error ◽  
Tropospheric Chemistry ◽  
Ozone Production ◽  
Optical Absorption Spectroscopy ◽  
The Tibetan Plateau ◽  
Mixing Ratios

Abstract. Mt. Waliguan Observatory (WLG) is a World Meteorological Organization (WMO) Global Atmosphere Watch (GAW) global baseline station in China. WLG is located at the northeastern part of the Tibetan Plateau (36∘17′ N, 100∘54′ E, 3816 m a.s.l.) and is representative of the pristine atmosphere over the Eurasian continent. We made long-term ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements at WLG during the period 2012–2015. In this study, we retrieve the differential slant column densities (dSCDs) and estimate the tropospheric background mixing ratios of different trace gases, including NO2, SO2, HCHO, and BrO, using the measured spectra at WLG. Averaging of 10 original spectra is found to be an “optimum option” for reducing both the statistical error of the spectral retrieval and systematic errors in the analysis. The dSCDs of NO2, SO2, HCHO, and BrO under clear-sky and low-aerosol-load conditions are extracted from measured spectra at different elevation angles at WLG. By performing radiative transfer simulations with the model TRACY-2, we establish approximate relationships between the trace gas dSCDs at 1∘ elevation angle and the corresponding average tropospheric background volume mixing ratios. Mixing ratios of these trace gases in the lower troposphere over WLG are estimated to be in a range of about 7 ppt (January) to 100 ppt (May) for NO2, below 0.5 ppb for SO2, between 0.4 and 0.9 ppb for HCHO, and lower than 0.3 ppt for BrO. The chemical box model simulations constrained by the NO2 concentration from our MAX-DOAS measurements show that there is a little net ozone loss (−0.8 ppb d−1) for the free-tropospheric conditions and a little net ozone production (0.3 ppb d−1) for the boundary layer conditions over WLG during summertime. Our study provides valuable information and data sets for further investigating tropospheric chemistry in the background atmosphere and its links to anthropogenic activities.

scholarly journals Dominant Modes of Tropospheric Ozone Variation over East Asia from GOME Observations

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Yi Liu ◽  
Yuli Zhang ◽  
Yong Wang ◽  
Chuanxi Liu ◽  
Zhaonan Cai ◽  
...  
Keyword(s):  
East Asia ◽  
Tropospheric Ozone ◽  
Asian Summer Monsoon ◽  
Principal Component ◽  
Total Variance ◽  
Ozone Production ◽  
The Tibetan Plateau ◽  
Westerly Jet ◽  
Sign Distribution ◽  
Subtropical Westerly Jet

The variation in tropospheric ozone over East Asia was analyzed using tropospheric column ozone data measured by the Global Ozone Monitoring Experiment (GOME) satellite. An empirical orthogonal function (EOF) analysis was carried out to derive the dominant modes of the variation in the tropospheric ozone volume-mixing ratio (TOVMR). The EOF1 mode, which explained 61.5% of the total variance, showed a same-sign distribution over all of East Asia, with a belt of enhanced ozone concentrations around 40°N. The principal component of EOF1 (PC1) suggested that photochemical ozone production together with Brewer-Dobson circulation and subtropical westerly jet plays important roles in modulating the seasonal variation of the TOVMR; ozone-rich air produced by photochemical processes was transported from the stratosphere to the troposphere by BD circulation and this ozone-rich air was then blocked by the subtropical westerly jet and accumulated north of the jet. The EOF2 mode explained 29.2% of the total variance with an opposite-sign pattern on the north and south side of 35°N. When anticyclonic circulation transported ozone-poor air from the upwelling area over the Bay of Bengal towards the Tibetan Plateau during the onset of the Asian summer monsoon, tropospheric ozone in this region decreased dramatically.

scholarly journals Composite study of aerosol export events from East Asia and North America

2012 ◽  
Vol 12 (8) ◽  
pp. 21977-22022 ◽  
Author(s):  
Y. Luan ◽  
L. Jaeglé
Keyword(s):  
Boundary Layer ◽  
North America ◽  
East Asia ◽  
Transport Model ◽  
Lower Troposphere ◽  
Temporal Variations ◽  
The Arctic ◽  
Chemical Transport Model ◽  
Mean Values ◽  
Warm Conveyor Belts

Abstract. We use satellite observations of aerosol optical depth (AOD) from the Moderate Resolution Imaging Spectrometer (MODIS) together with the GEOS-Chem global chemical transport model to contrast export of aerosols from East Asia and North America during 2004–2010. The GEOS-Chem model reproduces the spatial distribution and temporal variations of Asian aerosol outflow generally well, although a low bias (−30%) is found in the model fine mode AOD. We use the model to identify 244 aerosol pollution export events from E. Asia and 251 export events from N. America over our 7-yr study period. When these events are composited by season, we find that the AOD in the outflow is enhanced by 50–100% relative to seasonal mean values. The composite Asian plume splits into one branch going poleward towards the Arctic, with the other crossing the Pacific in 6–8 days. A fraction of the aerosols is trapped in the subtropical Pacific High. The N. American plume travels to the northeast Atlantic, reaching Europe after 4–5 days. Part of the composite plume turns anticyclonically in the Azores High, where it slowly decays. Both the Asian and N. American export events are favored by a dipole structure in sea-level pressure anomalies, associated with mid-latitude cyclone activity over the respective source regions. The observed AOD in the E. Asian outflow exhibits stronger seasonality, with a spring maximum, than the N. American outflow, with a weak summer maximum. The large spring AOD in the Asian outflow is the result of enhanced sulfate and dust aerosol concentrations, but is also due to a larger export efficiency of sulfate and SO2 from the Asian boundary layer relative to the N. American boundary layer. While the N. American sulfate outflow is mostly found in the lower troposphere (1–3 km altitude), the Asian sulfate outflow occurs at higher altitudes (2–6 km). In the Asian outflow 42–59% of the sulfate column is present above 2 km altitude, with only 24–35% in the N. American outflow. We link this to the factor of 2–5 lower precipitation in the warm conveyor belts (WCB) of midlatitude cyclones over E. Asia compared to N. America. This relative lack of precipitation makes Asian WCB very efficient for injecting aerosols in the middle troposphere.

scholarly journals Stratospheric impact on the Northern Hemisphere winter and spring ozone interannual variability in the troposphere

2019 ◽  
Author(s):  
Junhua Liu ◽  
Jose M. Rodriguez ◽  
Luke D. Oman ◽  
Anne R. Douglass ◽  
Mark A. Olsen ◽  
...  
Keyword(s):  
North America ◽  
Tropospheric Ozone ◽  
Interannual Variation ◽  
Stratospheric Ozone ◽  
Lower Troposphere ◽  
The Arctic ◽  
Vertical Extent ◽  
Pinatubo Eruption ◽  
Tropospheric O3 ◽  
The Impact

Abstract. In this study we use O3 and stratospheric O3 tracer simulations from the high-resolution Goddard Earth Observing System, Version 5 (GEOS-5) Replay run (MERRA-2 GMI at 0.5° model resolution ~ 50 km) and observations from ozonesondes to investigate the interannual variation and vertical extent of the stratospheric ozone impact on tropospheric ozone. Our work focuses on the winter and spring seasons over North America and Europe. The model reproduces the observed interannual variation of tropospheric O3, except for the Pinatubo period from 1991 to 1995 over the region of North America. Ozonesonde data show a negative ozone anomaly in 1992–1994 following the Pinatubo eruption, with recovery thereafter. The simulated anomaly is only half the magnitude of that observed. Our analysis suggests that the simulated Stratosphere-troposphere exchange (STE) flux deduced from the analysis might be too strong over the North American (50° N–70° N) region after the Mt. Pinatubo eruption in the early 1990s, masking the impact of lower stratospheric O3 concentration on tropospheric O3. European ozonesonde measurements show a similar but weaker O3 depletion after the Mt. Pinatubo eruption, which is fully reproduced by the model. Analysis based on a stratospheric O3 tracer (StratO3) identifies differences in strength and vertical extent of stratospheric ozone influence on the tropospheric ozone interannual variation (IAV) between North America and Europe. Over North America, the StratO3 IAV has a significant impact on tropospheric O3 from the upper to lower troposphere and explains about 60 % and 66 % of simulated O3 IAV at 400 hPa, ~ 11 % and 34 % at 700 hPa in winter and spring respectively. Over Europe, the influence is limited to the middle to upper troposphere, and becomes much smaller at 700 hPa. The stronger and deeper stratospheric contributions in the tropospheric O3 IAV over North America shown by the model is likely related to ozonesondes' being closer to the polar vortex in winter with lower geopotential height, lower tropopause height, and stronger coupling to the Arctic Oscillation in the lower troposphere (LT) than over Europe.

scholarly journals Long-term Variations in Ozone Levels in the Troposphere and Lower Stratosphere over Beijing: Observations and Model Simulations

2020 ◽  
Author(s):  
Yuli Zhang ◽  
Mengchu Tao ◽  
Jinqiang Zhang ◽  
Yi Liu ◽  
Hongbin Chen ◽  
...  
Keyword(s):  
Tropospheric Ozone ◽  
Lower Stratosphere ◽  
Stratospheric Ozone ◽  
Lower Troposphere ◽  
Control Measures ◽  
Tropospheric Chemistry ◽  
Lagrangian Model ◽  
Positive Trend ◽  
Sudden Decrease

Abstract. Tropospheric ozone is both a major pollutant and a short-lived greenhouse gas and has therefore attracted much concern in recent years. The ozone profile in the troposphere and lower stratosphere over Beijing has been observed since 2002 by ozonesondes developed by the Institute of Atmospheric Physics. Increasing concentrations of tropospheric ozone from 2002 to 2010 measured by these balloon-based observations have been reported previously. As more observations are now available, we used these data to analyze the long-term variability of ozone over Beijing during the whole period from 2002 to 2018. The ozonesondes measured increasing concentrations of ozone from 2002 to 2012 in both the troposphere and lower stratosphere. There was a sudden decrease in observed ozone between 2011 and 2012. After this decrease, the increasing trend in ozone concentrations slowed down, especially in the mid-troposphere, where the positive trend became neutral. We used the Chemical Lagrangian Model of the Stratosphere (CLaMS) to determine the influence of the transport of ozone from the stratosphere to the troposphere on the observed ozone profiles. CLaMS showed a weak increase in the contribution of stratospheric ozone before the decrease in 2011–2012 and a much more pronounced decrease after this time. Because there is no tropospheric chemistry in CLaMS, the sudden decrease simulated by CLaMS indicates that a smaller downward transport of ozone from the stratosphere after 2012 may explain a significant part of the observed decrease in ozone in the mid-troposphere and lower stratosphere. However, the influence of stratospheric ozone in the lower troposphere is negligible in CLaMS and the hiatus in the positive trend after 2012 can be attributed to a reduction in ozone precursors as a result of stronger pollution control measures in Beijing.

Gliding Mammals of the World

2012 ◽  
Author(s):  
Stephen Jackson ◽  
Peter Schouten
Keyword(s):  
North America ◽  
East Asia ◽  
Central Africa ◽  
The Philippines ◽  
South East Asia ◽  
Horizontal Distance ◽  
Distribution Map ◽  
Flying Squirrels ◽  
The World ◽  
First Time

The world's gliding mammals are an extraordinary group of animals that have the ability to glide from tree to tree with seemingly effortless grace. There are more than 60 species of gliding mammals including the flying squirrels from Asia, Europe and North America, the scaly-tailed flying squirrels from central Africa and the gliding possums of Australia and New Guinea. But the most spectacular of all are the colugos – or so called flying lemurs – that occur throughout South-East Asia and the Philippines. Animals that glide from tree to tree descend at an angle of less than 45 degrees to the horizontal, while those that parachute descend at an angle greater than 45 degrees. Gliding is achieved by deflecting air flowing past well-developed gliding membranes, or patagia, which form an effective airfoil that allows the animal to travel the greatest possible horizontal distance with the least loss in height. The flying squirrels and scaly-tailed flying squirrels even have special cartilaginous spurs that extend either from the wrist or elbow, respectively, to help support the gliding membrane. Gliding Mammals of the World provides, for the first time, a synthesis of all that is known about the biology of these intriguing mammals. It includes a brief description of each species, together with a distribution map and a beautiful full-colour painting. An introduction outlines the origins and biogeography of each group of gliding mammals and examines the incredible adaptations that allow them to launch themselves and glide from tree to tree.

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