Noncoincident validation of Aura MLS observations using the Langley Research Center Lagrangian chemistry and transport model

We evaluate Aura Microwave Limb Sounder version 2.2 measurements of O3, HCl, and H2O with version 19 HALOE observations using a model-assisted, noncoincident intercomparison technique. Air parcels in the Langley Research Center Lagrangian chemistry and transport model (LCTM) are initialized from HALOE observations made during three different 3-week periods in 2004 and early 2005. The LCTM tracks the dynamical and photochemical evolution of the ensemble of air parcels following initialization. We show that the LCTM predictions agree closely with subsequent HALOE measurements not used to initialize the model, demonstrating the model’s capability to accurately propagate information from the HALOE observations. HALOE-initialized LCTM O3 predictions agree very well in the stratosphere with MLS measurements, with coincident zonal mean differences generally less than 10%. We find low biases in HCl of 10–30% relative to the MLS observations. We also find low biases with respect to MLS H2O of up to 15% in the upper and middle stratosphere and
30% low biases in the lower stratosphere/upper troposphere midlatitudes. We note some nonphysical vertical oscillations of MLS H2O in the tropical and midlatitude lower stratosphere that are not present in the HALOE-initialized LCTM output. The oscillations are smaller in version 2.2 than in previous versions. These results are generally consistent with published HALOE/MLS intercomparisons of these species using a traditional coincident validation technique. This consistency suggests that the traditional coincident validation results are applicable on daily temporal and zonal spatial scales.