| publications-1411 |
PEER REVIEWED ARTICLE |
2014 |
B. Vogel , G. Günther , R. Müller , J.-U. Grooß , P. Hoor , M. Krämer , S. Müller , A. Zahn , M. Riese |
Fast transport from Southeast Asia boundary layer sources to northern Europe: rapid uplift in typhoons and eastward eddy shedding of the Asian monsoon anticyclone |
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10.5194/acp-14-12745-2014 |
Uncategorized |
Groundwater |
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Abstract. Enhanced tropospheric trace gases such as CO, CH4 and H2O and reduced stratospheric O3 were measured in situ in the lowermost stratosphere over northern Europe on 26 September 2012 during the TACTS aircraft campaign. The measurements indicate that these air masses clearly differ from the stratospheric background. The calculation of 40-day backward trajectories with the trajectory module of the CLaMS model shows that these air masses are affected by the Asian monsoon anticyclone. Some air masses originate from the boundary layer in Southeast Asia/West Pacific and are rapidly lifted (1–2 days) within a typhoon up to the outer edge of the Asian monsoon anticyclone. Afterwards, the air parcels are entrained by the anticyclonic circulation of the Asian monsoon. The subsequent long-range transport (8–14 days) of enhanced water vapour and pollutants to the lowermost stratosphere in northern Europe is driven by eastward transport of tropospheric air from the Asian monsoon anticyclone caused by an eddy shedding event. We found that the combination of rapid uplift by a typhoon and eastward eddy shedding from the Asian monsoon anticyclone is a novel fast transport pathway that may carry boundary emissions from Southeast Asia/West Pacific within approximately 5 weeks to the lowermost stratosphere in northern Europe. |
603557 |
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| publications-1412 |
PEER REVIEWED ARTICLE |
2016 |
Markus Kunze , Peter Braesicke , Ulrike Langematz , Gabriele Stiller |
Interannual variability of the boreal summer tropical UTLS in observations and CCMVal-2 simulations |
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10.5194/acp-16-8695-2016 |
Uncategorized |
Groundwater |
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Abstract. During boreal summer the upper troposphere/lower stratosphere (UTLS) in the Northern Hemisphere shows a distinct maximum in water vapour (H2O) mixing ratios and a coincident minimum in ozone (O3) mixing ratios, both confined within the Asian monsoon anticyclone (AMA). This well-known feature has been related to transport processes emerging above the convective systems during the Asian summer monsoon (ASM), further modified by the dynamics of the AMA. We compare the ability of chemistry–climate models (CCMs) to reproduce the climatological characteristics and variability of H2O, O3, and temperature in the UTLS during the boreal summer with MIPAS satellite observations and ERA-Interim reanalyses. By using a multiple linear regression model the main driving factors, the strength of the ASM, the quasi-biennial oscillation (QBO), and the El Niño–Southern Oscillation (ENSO), are separated. The regression patterns related to ENSO show a coherent, zonally asymmetric signal for temperatures and H2O mixing ratios for ERA-Interim and the CCMs and suggest a weakening of the ASM during ENSO warm events. The QBO modulation of the lower-stratospheric temperature near the Equator is well represented as a zonally symmetric pattern in the CCMs. Changes in H2O and O3 mixing ratios are consistent with the QBO-induced temperature and circulation anomalies but less zonally symmetric than the temperature pattern. Regarding the ASM, the results of the regression analysis show for ERA-Interim and the CCMs enhanced H2O and reduced O3 mixing ratios within the AMA for stronger ASM seasons. The CCM results can further confirm earlier studies which emphasize the importance of the Tibetan Plateau/southern slope of the Himalayas as the main source region for H2O in the AMA. The results suggest that H2O is transported towards higher latitudes at the north-eastern edge of the AMA rather than towards low equatorial latitudes to be fed into the tropical pipe. |
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| publications-1413 |
PEER REVIEWED ARTICLE |
2016 |
Ann-Sophie Tissier , Bernard Legras |
Convective sources of trajectories traversing the tropical tropopause layer |
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10.5194/acp-16-3383-2016 |
Uncategorized |
Uncategorized |
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Abstract. Transit properties across the tropical tropopause layer are studied using extensive forward and backward Lagrangian diabatic trajectories between cloud tops and the reference surface 380 K. After dividing the tropical domain into 11 subregions according to the distribution of land and convection, we estimate the contribution of each region to the upward mass flux across the 380 K surface and to the vertical distribution of convective sources and transit times over the period 2005–2008. The good agreement between forward and backward statistics is the basis of the results presented here. It is found that about 85 % of the tropical parcels at 380 K originate from convective sources throughout the year. From November to April, the sources are dominated by the warm pool which accounts for up to 70 % of the upward flux. During boreal summer, the Asian monsoon region is the largest contributor with similar contributions from the maritime and continental parts of the region; however, the vertical distributions and transit times associated with these two subregions are very different. Convective sources are generally higher over the continental part of the Asian monsoon region, with shorter transit times. We estimate the monthly averaged upward mass flux on the 380 K surface and show that the contribution from convective outflow accounts for 80 % on average and explains most of its seasonal variations. The largest contributor to the convective flux is the South Asian Pacific region (warm pool) at 39 % throughout the year followed by oceanic regions surrounding continental Asia at 18 % and Africa at 10.8 %. Continental Asian lowlands account for 8 %. The Tibetan Plateau is a minor overall contributor (0.8 %), but transport from convective sources in this region is very efficient due to its central location beneath the Asian upper level anticyclone. The core results are robust to uncertainties in data and methods, but the vertical source distributions and transit times exhibit some sensitivity to the representations of cloud tops and heating rates. The main sensitivity is to the radiative heating rates which vary among reanalyses. |
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| publications-1414 |
PEER REVIEWED ARTICLE |
2016 |
Thibaut Dauhut , Jean-Pierre Chaboureau , Juan Escobar , Patrick Mascart |
Giga-LES of Hector the Convector and Its Two Tallest Updrafts up to the Stratosphere |
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10.1175/jas-d-16-0083.1 |
Uncategorized |
Groundwater |
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Abstract The dynamics of Hector the Convector, which overshot into the stratosphere on 30 November 2005 over the Tiwi Islands, Australia, is investigated using a giga-large-eddy simulation with a 100-m cubic mesh. Individual updrafts, defined as 3D objects with vertical velocity above 10 m s−1 are identified. Among the 20 000 updrafts formed during the most intense phase, only a dozen were more than 4 km tall. The two tallest updrafts accounted for more than 90% of the total vertical mass flux through the tropical tropopause layer. Their locations were determined by low-level convergence lines first created by the sea breeze in the morning, then enhanced by cold pools due to cumulus congestus. They finally reinforced each other as they moved inland and intersected. The two tallest updrafts that overshot the tropopause were contrasted with those occurring 1 h earlier and later. They presented larger widths (up to 8 km), greater buoyancy (up to 0.1 m s−2), stronger vertical velocities (up to 50 m s−1), and larger hydrometeor contents (more than 10 g kg−1). They kept their core weakly diluted on their way to the stratosphere with an entrainment rate as low as 0.08 km−1. Both the low-level convergence lines intensified by cold pools and the reduced mixing in the troposphere were found to be the determinant for the transition from deep to very deep convection. |
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| publications-1415 |
PEER REVIEWED ARTICLE |
2016 |
T. Dinh , A. Podglajen , A. Hertzog , B. Legras , R. Plougonven |
Effect of gravity wave temperature fluctuations on homogeneous ice nucleation in the tropical tropopause layer |
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10.5194/acp-16-35-2016 |
Simulation & Modeling |
River Basins |
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Abstract. The impact of high-frequency fluctuations of temperature on homogeneous nucleation of ice crystals in the vicinity of the tropical tropopause is investigated using a bin microphysics scheme for air parcels. The imposed temperature fluctuations come from measurements during isopycnic balloon flights near the tropical tropopause. The balloons collected data at high frequency, guaranteeing that gravity wave signals are well resolved.With the observed temperature time series, the numerical simulations with homogeneous freezing show a full range of ice number concentration (INC) as previously observed in the tropical upper troposphere. In particular, a low INC may be obtained if the gravity wave perturbations produce a non-persistent cooling rate (even with large magnitude) such that the absolute change in temperature remains small during nucleation. This result is explained analytically by a dependence of the INC on the absolute drop in temperature (and not on the cooling rate). This work suggests that homogeneous ice nucleation is not necessarily inconsistent with observations of low INCs. |
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| publications-1416 |
PEER REVIEWED ARTICLE |
2017 |
Sinikka T. Lennartz , Christa A. Marandino , Marc von Hobe , Pau Cortes , Birgit Quack , Rafel Simo , Dennis Booge , Andrea Pozzer , Tobias Steinhoff |
Direct oceanic emissions unlikely to account for the missing source of atmospheric carbonyl sulfide |
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10.5194/acp-17-385-2017 |
Simulation & Modeling |
Groundwater |
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Abstract. The climate active trace-gas carbonyl sulfide (OCS) is the most abundant sulfur gas in the atmosphere. A missing source in its atmospheric budget is currently suggested, resulting from an upward revision of the vegetation sink. Tropical oceanic emissions have been proposed to close the resulting gap in the atmospheric budget. We present a bottom-up approach including (i) new observations of OCS in surface waters of the tropical Atlantic, Pacific and Indian oceans and (ii) a further improved global box model to show that direct OCS emissions are unlikely to account for the missing source. The box model suggests an undersaturation of the surface water with respect to OCS integrated over the entire tropical ocean area and, further, global annual direct emissions of OCS well below that suggested by top-down estimates. In addition, we discuss the potential of indirect emission from CS2 and dimethylsulfide (DMS) to account for the gap in the atmospheric budget. This bottom-up estimate of oceanic emissions has implications for using OCS as a proxy for global terrestrial CO2 uptake, which is currently impeded by the inadequate quantification of atmospheric OCS sources and sinks. |
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| publications-1417 |
PEER REVIEWED ARTICLE |
2016 |
Aurélien Podglajen , Riwal Plougonven , Albert Hertzog , Bernard Legras |
A modelling case study of a large-scale cirrus in the tropical tropopause layer |
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10.5194/acp-16-3881-2016 |
Uncategorized |
Uncategorized |
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Abstract. We use the Weather Research and Forecast (WRF) model to simulate a large-scale tropical tropopause layer (TTL) cirrus in order to understand the formation and life cycle of the cloud. This cirrus event has been previously described through satellite observations by Taylor et al. (2011). Comparisons of the simulated and observed cirrus show a fair agreement and validate the reference simulation regarding cloud extension, location and life time. The validated simulation is used to understand the causes of cloud formation. It is shown that several cirrus clouds successively form in the region due to adiabatic cooling and large-scale uplift rather than from convective anvils. The structure of the uplift is tied to the equatorial response (equatorial wave excitation) to a potential vorticity intrusion from the midlatitudes. Sensitivity tests are then performed to assess the relative importance of the choice of the microphysics parameterization and of the initial and boundary conditions. The initial dynamical conditions (wind and temperature) essentially control the horizontal location and area of the cloud. However, the choice of the microphysics scheme influences the ice water content and the cloud vertical position. Last, the fair agreement with the observations allows to estimate the cloud impact in the TTL in the simulations. The cirrus clouds have a small but not negligible impact on the radiative budget of the local TTL. However, for this particular case, the cloud radiative heating does not significantly influence the simulated dynamics. This result is due to (1) the lifetime of air parcels in the cloud system, which is too short to significantly influence the dynamics, and (2) the fact that induced vertical motions would be comparable to or smaller than the typical mesoscale motions present. Finally, the simulation also provides an estimate of the vertical redistribution of water by the cloud and the results emphasize the importance in our case of both rehydration and dehydration in the vicinity of the cirrus. |
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| publications-1418 |
PEER REVIEWED ARTICLE |
2015 |
B. Vogel , G. Günther , R. Müller , J.-U. Grooß , M. Riese |
Impact of different Asian source regions on the composition of the Asian monsoon anticyclone and of the extratropical lowermost stratosphere |
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10.5194/acp-15-13699-2015 |
Uncategorized |
Groundwater |
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Abstract. The impact of different boundary layer source regions in Asia on the chemical composition of the Asian monsoon anticyclone, considering its intraseasonal variability in 2012, is analysed by simulations of the Chemical Lagrangian Model of the Stratosphere (CLaMS) using artificial emission tracers. The horizontal distribution of simulated CO, O3, and artificial emission tracers for India/China are in good agreement with patterns found in satellite measurements of O3 and CO by the Aura Microwave Limb Sounder (MLS). Using in addition, correlations of artificial emission tracers with potential vorticity demonstrates that the emission tracer for India/China is a very good proxy for spatial distribution of trace gases within the Asian monsoon anticyclone. The Asian monsoon anticyclone constitutes a horizontal transport barrier for emission tracers and is highly variable in location and shape. From the end of June to early August, a northward movement of the anticyclone and, during September, a strong broadening of the spatial distribution of the emission tracer for India/China towards the tropics are found. In addition to the change of the location of the anticyclone, the contribution of different boundary source regions to the composition of the Asian monsoon anticyclone in the upper troposphere strongly depends on its intraseasonal variability and is therefore more complex than hitherto believed. The largest contributions to the composition of the air mass in the anticyclone are found from northern India and Southeast Asia at a potential temperature of 380 K. In the early (mid-June to mid-July) and late (September) period of the 2012 monsoon season, contributions of emissions from Southeast Asia are highest; in the intervening period (early August), emissions from northern India have the largest impact. Our findings show that the temporal variation of the contribution of different convective regions is imprinted in the chemical composition of the Asian monsoon anticyclone. Air masses originating in Southeast Asia are found both within and outside of the Asian monsoon anticyclone because these air masses experience, in addition to transport within the anticyclone, upward transport at the southeastern flank of the anticyclone and in the tropics. Subsequently, isentropic poleward transport of these air masses occurs at around 380 K with the result that the extratropical lowermost stratosphere in the Northern Hemisphere is flooded by the end of September with air masses originating in Southeast Asia. Even after the breakup of the anticyclonic circulation (around the end of September), significant contributions of air masses originating in India/China are still found in the upper troposphere over Asia. Our results demonstrate that emissions from India, China, and Southeast Asia have a significant impact on the chemical composition of the lowermost stratosphere of the Northern Hemisphere, in particular at the end of the monsoon season in September/October 2012. |
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| publications-1419 |
PEER REVIEWED ARTICLE |
2016 |
Marta Abalos , Bernard Legras , Emily Shuckburgh |
Interannual variability in effective diffusivity in the upper troposphere/lower stratosphere from reanalysis data |
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10.1002/qj.2779 |
Data Management & Analytics |
Precipitation & Ecological Systems |
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The effective diffusivity based on passive tracer advection is used to evaluate the long‐term mixing properties for the period 1980–2012 in the lower stratosphere and upper troposphere (UTLS) using data from the ERA‐Interim reanalysis. The regions of strongest interannual variability in effective diffusivity coincide with the regions of strong climatological mixing, such as the winter and spring midlatitude stratosphere, the polar lowermost stratosphere and around the edge of the subtropical jets (especially in summer). The annular modes dominate the variability in the winter polar vortices, and the Quasi‐Biennial Oscillation in the tropical stratosphere. El Niño/Southern Oscillation modulates the strength of mixing across the subtropical jets, and has a significant impact on mixing in the summer subtropical lower stratosphere. Long‐term trends show a vertical shift in the mixing consistent with the effect of ozone depletion on the zonal wind in the austral summer polar stratosphere. Other significant trends include increased mixing in the austral surf zone and a dipolar pattern in the boreal summer and autumn, with mixing increased on the equatorward part of the subtropical jet and reduced just above. The results are highly consistent with those from the JRA‐55 reanalysis when the same horizontal resolution is used. The calculations are also qualitatively consistent with effective diffusivity obtained directly from the potential vorticity field and, in the UTLS, they are broadly consistent with those obtained from the ozone field. |
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| publications-1420 |
PEER REVIEWED ARTICLE |
2014 |
David Barriopedro , Natalia Calvo |
On the Relationship between ENSO, Stratospheric Sudden Warmings, and Blocking |
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10.1175/jcli-d-13-00770.1 |
Data Management & Analytics |
Precipitation & Ecological Systems |
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Abstract This paper examines the influence of El Niño–Southern Oscillation (ENSO) on different aspects of major stratospheric sudden warmings (SSWs), focusing on the precursor role of blocking events. The results reveal an ENSO modulation of the blocking precursors of SSWs. European and Atlantic blocks tend to precede SSWs during El Niño (EN), whereas eastern Pacific and Siberian blocks are the preferred precursors of SSWs during La Niña (LN) winters. This ENSO preference for different blocking precursors seems to occur through an ENSO effect on regional blocking persistence, which in turn favors the occurrence of SSWs. The regional blocking precursors of SSWs during each ENSO phase also have different impacts on the upward propagation of planetary-scale wavenumbers 1 and 2; hence, they determine ENSO differences in the wavenumber signatures of SSWs. SSWs occurring during EN are preceded by amplification of wavenumber 1, whereas LN SSWs are predominantly associated to wavenumber-2 amplification. However, there is not a strong preference for splitting or displacement SSWs during any ENSO phase. This is mainly because during EN, splitting SSWs do not show a wavenumber-2 pattern. |
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