The seasonal and zonal differences in the temperature, circulation and composition of the tropical upper troposphere and lower stratosphere due to the MJO

Abstract Seasonal differences in the impact of the Madden–Julian oscillation (MJO) on tropical and extratropical upper troposphere–lower stratosphere (UTLS) temperature, circulation, and trace gases are examined using trace gases (ozone, carbon monoxide, and water vapor) and temperature from measurements from the Microwave Limb Sounder (MLS) and meteorological fields from the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2). During boreal winter months (November–February), atmospheric fields exhibit a well-known planetary-scale perturbation consistent with the upper-level flow modeled by Gill, with twin high and low pressure extratropical systems associated with a Rossby wave response. However, the circulation anomalies in the UTLS differ during boreal summer months (June–September), when background UTLS circulation north of the equator is dominated by the Asian summer monsoon anticyclone. The twin high and low pressure extratropical systems are much weaker but with a stronger equatorial Kelvin wave front that encircles the globe as the MJO propagates eastward. These differences are explained in terms of seasonal variations in vertically propagating Kelvin waves that strongly depend on the zonal structure of the climatological background winds. The trace gas response to the MJO is strongly coherent with circulation anomalies showing strong seasonal differences. The stronger equatorial Kelvin wave front during the summer produces enhanced upwelling in the tropical tropopause layer, resulting in significant cooling of this region, reduced ozone and water vapor, and enhanced carbon monoxide.

Download Full-text

Seasonal characteristics of trace gas transport into the extratropical upper troposphere and lower stratosphere

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-7073-2019 ◽

2019 ◽

Vol 19 (10) ◽

pp. 7073-7103 ◽

Cited By ~ 1

Author(s):

Yoichi Inai ◽

Ryo Fujita ◽

Toshinobu Machida ◽

Hidekazu Matsueda ◽

Yousuke Sawa ◽

...

Keyword(s):

Lower Stratosphere ◽

Trace Gases ◽

Source Region ◽

Lower Troposphere ◽

Trace Gas ◽

Air Masses ◽

Backward Trajectories ◽

Upper Troposphere ◽

Passive Behavior ◽

Seasonal Characteristics

Abstract. To investigate the seasonal characteristics of trace gas distributions in the extratropical upper troposphere and lower stratosphere (ExUTLS) as well as stratosphere–troposphere exchange processes, origin fractions of air masses originating in the stratosphere, tropical troposphere, midlatitude lower troposphere (LT), and high-latitude LT in the ExUTLS are estimated using 10-year backward trajectories calculated with European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim data as the meteorological input. Time series of trace gases obtained from ground-based and airborne observations are incorporated into the trajectories, thus reconstructing spatiotemporal distributions of trace gases in the ExUTLS. The reconstructed tracer distributions are analyzed with the origin fractions and the stratospheric age of air (AoA) estimated using the backward trajectories. The reconstructed distributions of SF6 and CO2 in the ExUTLS are linearly correlated with those of AoA because of their chemically passive behavior and quasi-stable increasing trends in the troposphere. Distributions of CH4, N2O, and CO are controlled primarily by chemical decay along the transport path from the source region via the stratosphere and subsequent mixing of such stratospheric air masses with tropospheric air masses in the ExUTLS.

Download Full-text

The governing processes and timescales of stratosphere-to-troposphere transport and its contribution to ozone in the Arctic troposphere

Atmospheric Chemistry and Physics ◽

10.5194/acp-9-3011-2009 ◽

2009 ◽

Vol 9 (9) ◽

pp. 3011-3025 ◽

Cited By ~ 33

Author(s):

Q. Liang ◽

A. R. Douglass ◽

B. N. Duncan ◽

R. S. Stolarski ◽

J. C. Witte

Keyword(s):

Lower Stratosphere ◽

Trace Gases ◽

Lower Troposphere ◽

Threshold Level ◽

The Arctic ◽

Trace Gas ◽

Seasonal Cycles ◽

Upper Troposphere ◽

Budget Analysis ◽

Wet Removal

Abstract. We used the seasonality of a combination of atmospheric trace gases and idealized tracers to examine stratosphere-to-troposphere transport and its influence on tropospheric composition in the Arctic. Maximum stratosphere-to-troposphere transport of CFCs and O3 occurs in April as driven by the Brewer-Dobson circulation. Stratosphere-troposphere exchange (STE) occurs predominantly between 40° N to 80° N with stratospheric influx in the mid-latitudes (30–70° N) accounting for 67–81% of the air of stratospheric origin in the Northern Hemisphere extratropical troposphere. Transport from the lower stratosphere to the lower troposphere (LT) takes three months on average, one month to cross the tropopause, the second month to travel from the upper troposphere (UT) to the middle troposphere (MT), and the third month to reach the LT. During downward transport, the seasonality of a trace gas can be greatly impacted by wet removal and chemistry. A comparison of idealized tracers with varying lifetimes suggests that when initialized with the same concentrations and seasonal cycles at the tropopause, trace gases that have shorter lifetimes display lower concentrations, smaller amplitudes, and earlier seasonal maxima during transport to the LT. STE contributes to O3 in the Arctic troposphere directly from the transport of O3 and indirectly from the transport of NOy. Direct transport of O3 from the stratosphere accounts for 78% of O3 in the Arctic UT with maximum contributions occurring from March to May. The stratospheric contribution decreases significantly in the MT/LT (20–25% of total O3) and shows a very weak March–April maximum. Our NOx budget analysis in the Arctic UT shows that during spring and summer, the stratospheric injection of NOy-rich air increases NOx concentrations above the 20 pptv threshold level, thereby shifting the Arctic UT from a regime of net photochemical ozone loss to one of net production with rates as high as +16 ppbv/month.

Download Full-text

Multivariate analysis of Kelvin wave seasonal variability in ECMWF L91 analyses

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-8313-2018 ◽

2018 ◽

Vol 18 (11) ◽

pp. 8313-8330 ◽

Cited By ~ 4

Author(s):

Marten Blaauw ◽

Nedjeljka Žagar

Keyword(s):

Multivariate Analysis ◽

Seasonal Variability ◽

Lower Stratosphere ◽

Shallow Water Equation ◽

Static Stability ◽

Boreal Summer ◽

Kelvin Wave ◽

Upper Troposphere ◽

Eastern Hemisphere ◽

Spherical Earth

Abstract. This paper presents a multivariate analysis of the linear Kelvin waves (KWs) represented by the operational 91-level ECMWF analyses in the 2007–2013 period, with a focus on seasonal variability. The applied method simultaneously filters KW wind and temperature perturbations in the continuously stratified atmosphere on the spherical Earth. The spatial filtering of the three-dimensional KW structure in the upper troposphere and lower stratosphere is based on the Hough harmonics using several tens of linearized shallow-water equation systems on the spherical Earth with equivalent depths ranging from 10 km to a few metres. Results provide the global KW energy spectrum. It shows a clear seasonal cycle with the KW activity predominantly in zonal wavenumbers 1–2, where up to 50 % more energy is observed during the solstice seasons in comparison with boreal spring and autumn. Seasonal variability in KWs in the upper troposphere and lower stratosphere is examined in relation to the background wind and stability. A spectral bandpass filtering is used to decompose variability into three period ranges: seasonal, intra-seasonal and intra-monthly variability components. Results reveal a slow seasonal KW component with a robust dipole structure in the upper troposphere with its position determined by the location of the dominant convective outflow throughout the seasons. Its maximal strength occurs during boreal summer when easterlies in the eastern hemisphere are strongest. The two other components represent vertically propagating KWs and are observed throughout the year with seasonal variability mostly found in the wave amplitudes being dependent on the seasonality of the background easterly winds and static stability.

Download Full-text

Large Anomalies in the Tropical Upper Troposphere Lower Stratosphere (UTLS) Trace Gases Observed during the Extreme 2015–16 El Niño Event by Using Satellite Measurements

Remote Sensing ◽

10.3390/rs11060687 ◽

2019 ◽

Vol 11 (6) ◽

pp. 687 ◽

Cited By ~ 7

Author(s):

S. Ravindrababu ◽

M. Ratnam ◽

Ghouse Basha ◽

Yuei-An Liou ◽

N. Reddy

Keyword(s):

21St Century ◽

El Niño ◽

Lower Stratosphere ◽

El Nino ◽

Trace Gases ◽

Equatorial Region ◽

Upper Troposphere ◽

El Niño Event ◽

Cold Point ◽

Tropical Upper Troposphere

It is well reported that the 2015–16 El Niño event is one of the most intense and long lasting events in the 21st century. The quantified changes in the trace gases (Ozone (O3), Carbon Monoxide (CO) and Water Vapour (WV)) in the tropical upper troposphere and lower stratosphere (UTLS) region are delineated using Aura Microwave Limb Sounder (MLS) and Atmosphere Infrared Radio Sounder (AIRS) satellite observations from June to December 2015. Prior to reaching its peak intensity of El Niño 2015–16, large anomalies in the trace gases (O3 and CO) were detected in the tropical UTLS region, which is a record high in the 21st century. A strong decrease in the UTLS (at 100 and 82 hPa) ozone (~200 ppbv) in July-August 2015 was noticed over the entire equatorial region followed by large enhancement in the CO (150 ppbv) from September to November 2015. The enhancement in the CO is more prevalent over the South East Asia (SEA) and Western Pacific (WP) regions where large anomalies of WV in the lower stratosphere are observed in December 2015. Dominant positive cold point tropopause temperature (CPT-T) anomalies (~5 K) are also noticed over the SEA and WP regions from the high-resolution Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) Global Position System (GPS) Radio Occultation (RO) temperature profiles. These observed anomalies are explained in the light of dynamics and circulation changes during El Niño.

Download Full-text

The governing processes and timescales of stratosphere-to-troposphere transport and its contribution to ozone in the Arctic troposphere

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-8-19377-2008 ◽

2008 ◽

Vol 8 (6) ◽

pp. 19377-19414

Author(s):

Q. Liang ◽

A. R. Douglass ◽

B. N. Duncan ◽

R. S. Stolarski ◽

J. C. Witte

Keyword(s):

Lower Stratosphere ◽

Trace Gases ◽

Lower Troposphere ◽

Threshold Level ◽

The Arctic ◽

Trace Gas ◽

Seasonal Cycles ◽

Upper Troposphere ◽

Budget Analysis ◽

Wet Removal

Abstract. We used the seasonality of a combination of atmospheric trace gases and idealized tracers to examine stratosphere-to-troposphere transport and its influence on tropospheric composition in the Arctic. Maximum stratosphere-to-troposphere transport of CFCs and O3 occurs in April as driven by the Brewer-Dobson circulation. Stratosphere-troposphere exchange (STE) occurs predominantly between 40° N to 80° N with stratospheric influx in the mid-latitudes (30–70° N) accounting for 67–81% of the air of stratospheric origin in the Northern Hemisphere extratropical troposphere. Transport from the lower stratosphere to the lower troposphere (LT) takes three months on average, one month to cross the tropopause, the second month to travel from the upper troposphere (UT) to the middle troposphere (MT), and the third month to reach the LT. During downward transport, the seasonality of a trace gas can be greatly impacted by wet removal and chemistry. A comparison of idealized tracers with varying lifetimes suggests that when initialized with the same concentrations and seasonal cycles at the tropopause, trace gases that have shorter lifetimes display lower concentrations, smaller amplitudes, and earlier seasonal maxima during transport to the LT. STE contributes to O3 in the Arctic troposphere directly from the transport of O3 and indirectly from the transport of NOy. Direct transport of O3 from the stratosphere accounts for 78% of O3 in the Arctic UT with maximum contributions occurring from March to May. The stratospheric contribution decreases significantly in the MT/LT (20–25% of total O3) and shows a very weak March–April maximum. Our NOx budget analysis in the Arctic UT shows that during spring and summer, the stratospheric injection of NOy-rich air increases NOx concentrations above the 20 pptv threshold level, thereby shifting the Arctic UT from a regime of net photochemical ozone loss to one of net production with rates as high as +16 ppbv/month.

Download Full-text

Mercury distribution in the upper troposphere and lower most stratosphere according to measurements by the IAGOS-CARIBIC observatory, 2014–2016

10.5194/acp-2017-1233 ◽

2018 ◽

Author(s):

Franz Slemr ◽

Andreas Weigelt ◽

Ralf Ebinghaus ◽

Johannes Bieser ◽

Carl A. M. Brenninkmeijer ◽

...

Keyword(s):

Large Scale ◽

Total Mercury ◽

Trace Gases ◽

Boreal Winter ◽

Signal Integration ◽

Upper Troposphere ◽

Cloud Scavenging ◽

Passenger Aircraft ◽

North And South America ◽

North And South

Abstract. Mercury was measured onboard the IAGOS-CARIBIC passenger aircraft since May 2005 until February 2016 during nearly monthly sequences of mostly four intercontinental flights from Germany to destinations in North and South America, Africa, and South and East Asia. Most of these mercury data were obtained using an internal default signal integration procedure of the Tekran instrument but since April 2014 more precise and accurate data were obtained using post-flight manual integration of the instrument raw signal. In this paper we use the latter data. Elevated upper tropospheric total mercury (TM) concentrations due to large scale biomass burning were observed in the upper troposphere (UT) at the equator and southern latitudes during the flights to Latin America and South Africa in boreal autumn (SON) and boreal winter (DJF). TM concentrations in the lowermost stratosphere (LMS) decrease with altitude above the thermal tropopause but the gradient is less steep than reported before. Seasonal variation of the vertical TM distribution in the UT and LMS is similar to that of other trace gases with surface sources and stratospheric sinks. Using speciation experiments, we show that nearly identical TM and gaseous elementary mercury (GEM) concentrations exist at and below the tropopause. Above the thermal tropopause GEM concentrations are almost always smaller than those of TM and the TM – GEM (i.e. Hg2+) difference increases up to ~ 40 % of TM at ~ 2 km and more above the thermal tropopause. Correlations with N2O as a reference tracer suggest stratospheric lifetimes of 72 ± 37 and 74 ± 27 yr for TM and GEM, respectively, comparable to the stratospheric lifetime of COS. This coincidence, combined with pieces of evidence from us and other researchers, corroborates the hypothesis that Hg2+ formed by oxidation in the stratosphere attaches to sulfate particles formed mainly by oxidation of COS and is removed with them from the stratosphere by air mass exchange, gravitational sedimentation, and cloud scavenging processes.

Download Full-text

Climatology and long-term evolution of ozone and carbon monoxide in the UTLS at northern mid-latitudes, as seen by IAGOS from 1995 to 2013

10.5194/acp-2017-778 ◽

2017 ◽

Cited By ~ 1

Author(s):

Yann Cohen ◽

Hervé Petetin ◽

Valérie Thouret ◽

Virginie Marécal ◽

Béatrice Josse ◽

...

Keyword(s):

Carbon Monoxide ◽

Lower Stratosphere ◽

Boreal Summer ◽

Brazilian Coast ◽

Seasonal Cycles ◽

Western Coast ◽

Data Set ◽

Upper Troposphere ◽

North East ◽

Wide Range

Abstract. In situ measurements in the upper troposphere – lower stratosphere (UTLS) are performed in the framework of the European research infrastructure IAGOS (In-service Aircraft for a Global Observing System) for ozone since 1994 and for carbon monoxide since 2002. The flight tracks cover a wide range of longitudes in the northern extratropics, extending from the North American western coast (125° W) to the eastern Asian coast (135° E), and more recently over the northern Pacific ocean. Different tropical regions are also sampled frequently, such as the Brazilian coast, central and southern Africa, southeastern Asia and the western Maritime Continent. As a result, a new set of climatologies for O3 (Aug. 1994–Dec. 2013) and CO (Dec. 2001–Dec. 2013) in the upper troposphere (UT), tropopause layer and lower stratosphere (LS) are made available, including quasi-global gridded horizontal distributions, and seasonal cycles over eight well sampled regions of interest in the northern extratropics. The seasonal cycles generally show a summertime maximum in O3 and a springtime maximum in CO in the UT, in contrast with the systematic springtime maximum in O3 and the quasi-absence of seasonal cycle of CO in the LS. This study highlights some regional variabilities in the UT notably (i) a west-east difference of O3 in boreal summer with up to 15 ppb more O3 over central Russia compared with northeast America, (ii) a systematic west-east gradient of CO from 60° E to 140° E (especially noticeable in spring and summer with about 5 ppb by 10 degrees longitude), (iii) a broad spring/summer maximum of CO over North East Asia, and (iv) a spring maximum of O3 over Western North America. Thanks to almost 20 years of O3 and 12 years of CO measurements, the IAGOS database is a unique data set to derive trends in the UTLS. Trends in O3 in the UT are positive and statistically significant in most regions, ranging from +0.25 to +0.45 ppb yr−1, characterized by the significant increase of the lowest values of the distribution. No significant trends of O3 are detected in the LS. Trends of CO in the UT, tropopause and LS are all negative and statistically significant. The estimated slopes range from −1.37 to −0.59 ppb yr−1 , with a nearly homogeneous decrease of the lowest values of the monthly distribution (fifth percentile) contrasting with the high inter-regional variability of the highest values (95th percentile).

Download Full-text

Modeling the transport of very short-lived substances into the tropical upper troposphere and lower stratosphere

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-9-18511-2009 ◽

2009 ◽

Vol 9 (5) ◽

pp. 18511-18543 ◽

Cited By ~ 2

Author(s):

J. Aschmann ◽

B. M. Sinnhuber ◽

E. L. Atlas ◽

S. M. Schauffler

Keyword(s):

Large Scale ◽

Lower Stratosphere ◽

Transport Model ◽

Three Dimensional ◽

Chemical Transport Model ◽

Heating Rates ◽

Model Calculations ◽

Upper Troposphere ◽

Mass Fluxes ◽

Tropical Upper Troposphere

Abstract. The transport of very short-lived substances into the tropical upper troposphere and lower stratosphere is investigated by a three-dimensional chemical transport model using archived convective updraft mass fluxes (or detrainment rates) from the European Centre for Medium-Range Weather Forecast's ERA-Interim reanalysis. Large-scale vertical velocities are calculated from diabatic heating rates. With this approach we explicitly model the large scale subsidence in the tropical troposphere with convection taking place in fast and isolated updraft events. The model calculations agree generally well with observations of bromoform and methyl iodide from aircraft campaigns and with ozone and water vapor from sonde and satellite observations. Using a simplified treatment of dehydration and bromine product gas washout we give a range of 1.6 to 3 ppt for the contribution of bromoform to stratospheric bromine, assuming a uniform source in the boundary layer of 1 ppt. We show that the most effective region for VSLS transport into the stratosphere is the West Pacific, accounting for about 55% of the bromine from bromoform transported into the stratosphere under the supposition of a uniformly distributed source.

Download Full-text