[1] Seasonal variations of several trace constituents near the tropopause are analyzed based on satellite measurements, and results are compared to a recent numerical model simulation. We examine methane, water vapor, and nitrogen oxides (NO x ) derived from Halogen Occultation Experiment (HALOE) satellite observations; these species have strong gradients near the tropopause, so that their seasonality is indicative of stratospheretroposphere exchange (STE) and circulation in the near-tropopause region. Model results are from the Model for Ozone and Related Chemical Tracers (MOZART) stratospheretroposphere chemical transport model (CTM). Results show overall good agreement between observations and model simulations for methane and water vapor, whereas nitrogen oxides near the tropopause are much lower in the model than suggested by HALOE data. The latter difference is probably related to the lightning and convective parameterizations incorporated in MOZART, which produce NO x maxima not near the tropopause, but in the upper troposphere. Constituent seasonal variations highlight the imporatance of the Northern Hemisphere (NH) summer monsoons as regions for transport into the lowermost stratosphere. In MOZART, there is clear evidence that air from the monsoon region is transported into the tropics and entrained into the upward BrewerDobson circulation, bypassing the tropical tropopause.

The risk of HGD increases with the size of PGA, tubulovillous architecture and the presence of AIG as well as mixed immunophenotype. As the overall local recurrence rate is less than 10%, PGAs may be treated conservatively, but they should be excised completely if possible, particularly if they are large or show high-grade features.

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Non-conventional dysplasias of the tubular gut: a review and illustration of their histomorphological spectrumThe increasing use of gastrointestinal endoscopic procedures has led to the recognition by histopathologists of non-conventional (or special-type) dysplasias of the gastrointestinal tract. These lesions can be recognised in association with prevalent underlying gastrointestinal conditions, such as Barrett oesophagus, chronic atrophic gastritis, and inflammatory bowel disease. The diagnosis of these special types can be challenging, and their biological behaviours are not fully characterised. The aim of this review is to provide a global view of non-conventional dysplastic lesions observed in the various segments of the tubular gastrointestinal tract and describe their salient features. Furthermore, as the clinical implications of these various subtypes have not been broadly tested in practice and are not represented in most management guidelines, we offer guidance on the best management practices for these lesions.

Concentrations and distributions of stratospheric aerosol, hydrogen fluoride and ozone from the Halogen Occultation Experiment (HALOE) on the Upper Atmosphere Research Satellite (UARS) are used to investigate features associated with transport by the secondary meridional circulation induced by the quasi‐biennial oscillation (QBO). The points of maxima in the divergence and convergence of the QBO‐induced meridional velocity at the equator are identified from the meridional gradients of the tracers. Such points can be identified from the tracer fields in the westerly shear zones but not in the easterly shear zones. The temporal variation of tracer concentration at the equator is determined mainly by vertical advection, which is significantly larger during the westerly shear phase of the QBO than during the easterly shear phase, since the QBO‐induced equatorial sinking motion amplifies the vertical gradient. Thus, the vertical advection associated with the secondary circulation has a stronger influence on the equatorial tracer variation during the westerly shear phase than during the easterly shear phase.