Climatology and small-scale structure of lower stratospheric N2O based on in situ observations

We derive seasonal mean distributions of N2O as a function of latitude and height from in situ measurements made by the airborne tunable laser absorpt ion spectrometer (ATLAS) instrument on board the NASA ER-2 aircraft. Season al means are also derived using an equivalent latitude coordinate which max imizes the information content and produces nearly pole-to-pole coverage. T he mean N2O fields are consistent with the Brewer-Dobson circulation, showi ng tropospheric values of N2O entering the tropical lower stratosphere and low values at the winter hemisphere poles. The analysis presented here is i ntended for use as a climatology for two- and three-dimensional modelers wi shing to evaluate the balance of transport processes affecting their models ' lower stratosphere. We also present some interesting features that have b een revealed by the high spatial resolution of the ATLAS measurements. Thes e include large gradients of N2O observed at the equatorward and poleward e dges of the surf zone and filaments less than 1 km thick identified during aircraft profiling. The results presented here demonstrate the unique natur e and high value of aircraft in situ data sets.