Climatologyand small-scalestructureof lower stratosphericNzO based on in situ observations

We derive seasonalmean distributionsof N20 as a function of latitude and heightfrom in situ measurements madeby the airbornetunablelaserabsorption spectrometer (ATLAS) instrumenton boardthe NASA ER-2 aircraft.Seasonalmeansare alsoderivedusingan equivalentlatitudecoordinatewhichmaximizesthe information contentand producesnearlypole-to-polecoverage.The mean N20 fieldsare consistent with the Brewer-Dobsoncirculation,showingtroposphericvaluesof N20 enteringthe tropicallower stratosphere and low valuesat the winter hemispherepoles.The analysis presentedhere is intendedfor useas a climatologyfor two- and three-dimensional modelerswishingto evaluatethe balanceof transportprocesses affectingtheir models' lower stratosphere.We alsopresentsomeinterestingfeaturesthat havebeen revealedby the high spatialresolutionof the ATLAS measurements. Theseincludelarge gradientsof N20 observedat the equatorwardand polewardedgesof the surfzone and filamentsless than 1 km thick identifiedduringaircraft profiling.The resultspresentedhere demonstratethe uniquenature and high value of aircraft in situ data sets.