Evidence of tropospheric layering: interleaved stratospheric and planetary boundary layer intrusions

International audienceWe present a case study of interleaving in the free troposphere of 4 layers of non-tropospheric origin, with emphasis on their residence time in the troposphere. Two layers are stratospheric intrusions at 4.7 and 2.2 km altitude with residence times of about 2 and 6.5 days, respectively. The two other layers at 7 and 3 km altitude were extracted from the maritime planetary boundary layer by warm conveyor belts associated with two extratropical lows and have residence times of about 2 and 5.75 days, respectively. The event took place over Frankfurt (Germany) in February 2002 and was observed by a commercial airliner from the MOZAIC programme with measurements of ozone, carbon monoxide and water vapour. Origins and residence times in the troposphere of these layers are documented with a trajectory and particle dispersion model. The combination of forward and backward simulations of the Lagrangian model allows the period of time during which the residence time can be assessed to be longer, as shown by the capture of the stratospheric-origin signature of the lowest tropopause fold just about to be completely mixed above the planetary boundary layer. This case study is of interest for atmospheric chemistry because it emphasizes the importance of coherent airstreams that produce laminae in the free troposphere and that contribute to the average tropospheric ozone. The interleaving of these 4 layers also provides the conditions for a valuable case study for the validation of global chemistry transport models used to perform tropospheric ozone budgets

Ozone profile observations in Houston, Texas (1994 - 2010) from aircraft, balloons, and satellites

Houston, Texas has long been an urban area plagued with high levels of surface ozone, particularly in spring and late summer. The combination of a large commuter population and one of the largest concentrations of petrochemical plants in the world results in abundant and nearly co-located sources of NOx and hydrocarbons. The location of Houston on the South Coast of the United States in a subtropical climate results in meteorological conditions that favor ozone production. Using MOZAIC (1994 - 2004), ozonesonde (2000, 2004 - 2010), and TES (2005 – 2010) data, we examine the evolution of ozone profiles over Houston during a period in which various strategies have been implemented to alleviate the ozone pollution problem. Using meteorological data from associated soundings and analyses, we identify and evaluate influences on the ozone profiles from natural and anthropogenic sources, as well as local and remote sources. We further investigate how these various influences have changed with time

A numerical study of tropical cross-tropopause transport by convective overshoots during the TROCCINOX golden day

International audienceObservations obtained during the Tropical Convection, Cirrus and Nitrogen Oxides (TROCCINOX) golden day have revealed the presence of ice particles up to 410 K (18.2 km) 2 km above the local tropopause. The case is investigated using a three-dimensional quadruply nested non-hydrostatic simulation and Meteosat Second Generation (MSG) observations. The simulation fairly well reproduces the measurements along the flight track. A reasonable agreement with MSG observations is also achieved: the 10.8-µm brightness temperature (BT) minimum of 187 K is reproduced (a value 6 K colder than the environmental cold-point temperature) as well as the positive BT difference between the 6.2- and 10.8-µm bands, an overshoot signature. The simulation produces several overshooting plumes up to 410 K yielding an upward transport of water vapour of a few tons per second across the tropical tropopause. The estimated mass flux agree with those derived from over tracer budgets indicating that convection transport mass across the tropopause

Midlatitude stratosphere - troposphere exchange as diagnosed by MLS O3 and MOPITT CO assimilated fields

International audienceThis paper presents a comprehensive characterization of a very deep stratospheric intrusion which occurred over the British Isles on 15 August 2007. The signature of this event is diagnosed using ozonesonde measurements over Lerwick, UK (60.14 N, 1.19 W) and is also well characterized using meteorological analyses from the global operational weather prediction model of Météo-France, ARPEGE. Modelled as well as assimilated fields of both ozone (O3) and carbon monoxide (CO) have been used in order to better document this event. O3 and CO from Aura/MLS and Terra/MOPITT instruments, respectively, are assimilated into the three-dimensional chemical transport model MOCAGE of Météo-France using a variational 3-DFGAT (First Guess at Appropriate Time) method. The validation of O3 and CO assimilated fields is done using selfconsistency diagnostics and by comparison with independent observations such as MOZAIC (O3 and CO), AIRS (CO) and OMI (O3). It particularly shows in the upper troposphere and lower stratosphere region that the assimilated fields are closer to MOZAIC than the free model run. The O3 bias between MOZAIC and the analyses is −11.5 ppbv with a RMS of 22.4 ppbv and a correlation coefficient of 0.93, whereas between MOZAIC and the free model run, the corresponding values are 33 ppbv, 38.5 ppbv and 0.83, respectively. In the same way, for CO, the bias, RMS and correlation coefficient between MOZAIC and the analyses are −3.16 ppbv, 13 ppbv and 0.79, respectively, whereas between MOZAIC and the free model run, the corresponding values are 33 ppbv, 38.5 ppbv and 0.83, respectively. In the same way, for CO, the bias, RMS and correlation coefficient between MOZAIC and the analyses are −3.16 ppbv, 13 ppbv and 0.79, respectively, whereas between MOZAIC and the free model they are 6.3 ppbv, 16.6 ppbv and 0.71, respectively. The paper also presents a demonstration of the capability of O3 and CO assimilated fields to better describe a stratosphere-troposphere exchange (STE) event in comparison with the free run modelled O3 and CO fields. Although the assimilation of MLS data improves the distribution of O3 above the tropopause compared to the free model run, it is not sufficient to reproduce the STE event well. Assimilated MOPITT CO allows a better qualitative description of the stratospheric intrusion event. The MOPITT CO analyses appear more promising than the MLS O3 analyses in terms of their ability to capture a deep STE event. Therefore, the results of this study open the perspectives for using MOPITT CO in the STE studies

Circulation ageostrophique dans les systemes jet-fronts: une etude prospective du couplage dynamique haute et basse troposphere

INIST T 73863 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc

Analysis and diagnosis of the composition of ageostrophic circulations in jet-front systems

International audienc

Rossby wave interactions with Mediterranean and subtropical latitudes

International audienceThe downstream influence of a Rossby wave on weather conditions in the Mediterranean and North Africa is studied. The objective is to gain a better understanding of the atmospheric processes in these regions and to improve their quantification. The emphasis is placed on high-impact weather events to improve numerical forecasts and warnings about these hazardous weather phenomena. For this purpose, 4 days from 5 to 8 February 1997 are used to investigate both a Mediterranean low and a subtropical African convective situation. Sensitivity studies, using a potential vorticity inversion tool associated with the French atmospheric model ARPEGE, are presented. The Mediterranean surface low under study is shown to be associated with the mid-latitude upper level potential vorticity anomaly, itself associated with a Rossby wave. A subtropical convective cell is shown to be related to upward vertical motions associated with a cut-off low; this cut-off low coming from a mid-latitude Rossby wave

Analysis of the tropospheric ozone column variations at mid northern latitudes MOZAIC sites (1994-2004).

(20-24 juin 2004