P. Siegmund

Tracer correlations in the northern high latitude lowermost stratosphere: Influence of cross-tropopause mass exchange

We present an analysis of trace gas correlations in the lowermost stratosphere. In-situ aircraft measurements of CO, N(2)O, NO(y) and O(3) Obtained during the STREAM 1997 winter campaign, have been used to investigate the role of cross-tropopause mass exchange on tracer-tracer relations. At altitudes several;kilometers above the local tropopause, undisturbed stratospheric air was found with NO(y)/NO(y)* ratios close to unity, NO(y)/O(3) about 0.003 - 0.006 and CO mixing ratios as low as 20 ppbv (NO(y)* is a proxy for total reactive nitrogen derived from NO(y)-N(2)O relations measured in the stratosphere). Mixing of tropospheric-air into the lowermost stratosphere has been identified by enhanced ratios of NO(y)/NO(y)* and NO(y)/O(3), and from scatter plots of CO versus O(3). The enhanced NO(y)/O(3) ratio in the lowermost stratospheric mixing zone points to a reduced efficiency of O(3) formation from aircraft NO(x) emissions.

A Simulation of the Separate Climate Effects of Middle-Atmospheric and Tropospheric CO2 Doubling

Abstract The separate climate effects of middle-atmospheric and tropospheric CO2 doubling have been simulated and analyzed with the ECHAM middle-atmosphere climate model. To this end, the CO2 concentration has been separately doubled in the middle-atmosphere, the troposphere, and the entire atmosphere, and the results have been compared to a control run. During NH winter, the simulated uniformly doubled CO2 climate shows an increase of the stratospheric residual circulation, a small warming in the Arctic lower stratosphere, a weakening of the zonal winds in the Arctic middle-atmosphere, an increase of the NH midlatitude tropospheric westerlies, and a poleward shift of the SH tropospheric westerlies. The uniformly doubled CO2 response in most regions is approximately equal to the sum of the separate responses to tropospheric and middle-atmospheric CO2 doubling. The increase of the stratospheric residual circulation can be attributed for about two-thirds to the tropospheric CO2 doubling and one-third to the...

Stratosphere‐troposphere exchange: A model and method intercomparison

This paper presents one of the first extensive intercomparisons of models and methods used for estimating stratosphere-troposphere exchange (STE). The study is part of the European Union project Influence of Stratosphere Troposphere Exchange in a Changing Climate on Atmospheric Transport and Oxidation Capacity (STACCATO). Nine different models and methods, including three trajectory methods, one Eulerian method, two Lagrangian and one Eulerian transport model, and two general circulation models applied the same initialization. Stratospheric and tropospheric tracers have been simulated, and the tracer mass fluxes have been calculated through the tropopause and the 700 hPa surface. For a 12-day case study over Europe and the northeast Atlantic the simulated tracer mass fluxes have been intercompared. For this case the STE simulations show the same temporal evolution and the same geographical pattern of STE for most models and methods, but with generally different amplitudes (up to a factor of 4). On the other hand, for some simulations also the amplitudes are very similar.

Infrasonic signature of the 2009 major sudden stratospheric warming

The study of infrasound is experiencing a renaissance since it was chosen as a verification technique for the Comprehensive Nuclear-Test-Ban Treaty. The success of the verification technique strongly depends on knowledge of upper atmospheric processes. The ability of infrasound to probe the upper atmosphere starts to be exploited, taking the field beyond its monitoring application. Processes in the stratosphere couple to the troposphere and influence our daily weather and climate. Infrasound delivers actual observations on the state of the stratosphere with a high spatial and temporal resolution. Here we show the infrasonic signature, passively obtained, of a drastic change in the stratosphere due to the major sudden stratospheric warming (SSW) of January 2009. With this study, we infer the enormous capacity of infrasound in acoustic remote sensing of stratospheric processes on a global scale with surface based instruments.

Chlorine activation and ozone destruction in the northern lowermost stratosphere

We report aircraft measurements from the Stratosphere-Troposphere Experiments by Aircraft Measurements (STREAM) II campaign, performed during February 1995 from Kiruna, northern Sweden, near 67 degrees N latitude. We have measured trace species, e.g., O-3, nitrogen compounds, HCl, hydrocarbons, CO, ice particles. and aerosols, to characterize the chemical conditions of the lowermost stratosphere at altitudes up to similar to 12.5 km. From the observation of anomalously high CO/C2H6 ratios, caused by enhanced C2H6 breakdown, we derive that heterogeneous chlorine activation has occurred. This has liberated a diurnal mean Cl concentration up to 1.0 x 10(4) atoms cm(-3), which efficiently destroys ozone. We also infer that much of the Cl activation has taken place on ice crystals above the tropopause. The measured crystal number densities were typical of thin cirrus. Model calculations suggest that heterogeneous chlorine conversion on ice crystals, in addition to that on liquid aerosols, may contribute significantly to ozone destruction in the middle- and high-latitude lowermost stratosphere.

Highly elevated carbon monoxide concentrations in the upper troposphere and lowermost stratosphere at northern midlatitudes during the STREAM II summer campaign in 1994

Abstract During the second Stratosphere Troposphere Experiment by Aircraft Measurements (STREAM II) five flights up to 12 km altitude were performed over the North Sea, Great Britain, The Netherlands, and Germany, with a Cessna Citation II twin jet aircraft during the period 20–29 July 1994. Carbon monoxide (CO) concentrations in the lowermost stratosphere, which were measured by tunable diode laser absorption spectroscopy, varied between typical background values around 40 parts per billion by volume (ppbv) and highly elevated levels of up to 300 ppbv. The high CO concentrations were observed before a cold front passed over western Europe. The enhanced CO abundance was most probably caused by boreal fires in Canada in connection with convective mixing and subsequent horizontal advection over the North Atlantic Ocean.

Observations of high concentrations of total reactive nitrogen (NO y ) and nitric acid (HNO3) in the lower Arctic stratosphere during the Stratosphere‐Troposphere Experiment by Aircraft Measurements (STREAM) II campaign in February 1995

Simultaneous in situ measurements of NO y , HNO 3 , O 3 , N 2 O, and CO have been performed in the lower stratosphere during the Stratosphere-Troposphere Experiment by Aircraft Measurements (STREAM) II intensive winter campaign in February 1995 from Kiruna airport (northern Sweden) with a Cessna Citation II twinjet aircraft up to a maximum altitude of 12.8 km. The flights were coordinated with the Arctic Second European Stratospheric Arctic and Midlatitude Experiment (SESAME) winter campaign. Strongly elevated levels of total reactive nitrogen (NO Y ) and its most abundant contributing species, nitric acid (HNO 3 ), with mixing ratios up to 9 parts per billion by volume (ppbv), were observed during all flights at altitudes near 12 km. On average, the measured NO concentrations exceed the expected levels by a factor of 2-3. Normal background O Y has been calculated from observed N 2 O mixing ratios using the NO Y -N 2 O correlation reported for the undisturbed northern hemisphere. This indicates that subsidence of air in the vortex alone cannot explain these findings. We propose that the elevated NO Y concentrations were caused by nitrification of the lower stratosphere associated with sedimentation and evaporation of polar stratospheric cloud particles that carry down HNO 3 from higher altitudes, that is, from altitudes up to about 25 km.

In situ trace gas and particle measurements in the summer lower stratosphere during STREAM II : Implications for O-3 production

In situ aircraft measurements of O3, CO,HNO3, and aerosol particles are presented,performed over the North Sea region in the summerlower stratosphere during the STREAM II campaign(Stratosphere Troposphere Experiments by AircraftMeasurements) in July 1994. Occasionally, high COconcentrations of 200-300 pbbv were measured in thelowermost stratosphere, together with relatively highHNO3 concentrations up to 1.6 ppbv. The particlenumber concentration (at standard pressure andtemperature) between 0.018-1 μm decreased acrossthe tropopause, from >1000 cm-3 in the uppertroposphere to <500 cm-3 in the lowermoststratosphere. Since the CO sources are found in thetroposphere, the elevated CO mixing ratios areattributed to mixing of polluted tropospheric air intothe lowermost extratropical stratosphere. Further wehave used a chemical model to illustrate that nitrogenoxide reservoir species (mainly HNO3) determinethe availability of NOx (=NO + NO2) andtherefore largely control the total net O3production in the lower kilometers of thestratosphere. Model simulations, applying additionalNOx perturbations from aircraft, show that theO3 production efficiency of NOx is smallerthan previously assumed, under conditions withrelatively high HNO3 mixing ratios, as observedduring STREAM II. The model simulations furthersuggest a relatively high O3 productionefficiency from CO oxidation, as a result of therelatively high ambient HNO3 and NOxconcentrations, implying that upward transport of COrich air enhances O3 production in the lowermoststratosphere. Analysis of the measurements and themodel calculations suggest that the lowermoststratosphere is a transition region in which thechemistry deviates from both the upper troposphere andlower stratosphere.

Nitric acid (HNO3) in the upper troposphere and lower stratosphere at midlatitudes: New results from aircraft‐based mass spectrometric measurements

Extensive measurements of gaseous nitric acid (HNO 3 ) have been performed in the upper troposphere and lower stratosphere using aircraft-based ion-molecule reaction mass spectrometry (IMRMS). The measurements, which took place in summer and winter between November 1994 and July 1996, cover latitudes between 29°N and 57°N and altitudes between 5.5 and 13 km. According to meteorological analyses, potential vorticity values up to 9.5 PVU (1 PVU = 10 -6 m 2 s -1 K kg -1 ) were reached. Stratospheric HNO 3 mixing ratios ranged between 300 and 2200 parts per trillion by volume (pptv). In the upper troposphere, nitric acid mixing ratios ranged between 100 and 2000 pptv, with the largest values influenced by fast vertical transport from the planetary boundary layer. These values exceed previous measurements and model calculations. The relatively high upper tropospheric nitric acid mixing ratio indicates a large rate for NO recycling from gaseous nitric acid, and possibly also an increased efficiency of aerosol activation, which may lead to an increased albedo of cirrus clouds.

Stratospheric Polar Cap Mean Height and Temperature as Extended-Range Weather Predictors

Abstract The skill of stratospheric and tropospheric predictors in predicting near-surface quantities at the extended range (∼10 days–2 months) has been investigated, using 40 yr of reanalysis data from the European Centre for Medium-Range Weather Forecasts. The predictors are 1) the geopotential height (Z) at various levels, 2) the difference between Z and the 1000-hPa geopotential [Z − Z(1000)], and 3) the temperature at various levels. The predictors are averages over the area north of 65°N. The predictands are Z(1000) averaged over the same area and geographical fields of several near-surface quantities. The predictive skill has been investigated for different lead times between predictor and predictand and different averaging periods of the predictor and the predictand. The results show that the predictive skill of Z in the troposphere is mainly due to the predictive skill of sea level pressure, whereas the predictive skill of Z in the stratosphere is mainly due to the predictive skill of stratospher...