Abstract
The hydrogen fluoride (HF) molecule is important as a tracer and for study of chlorine input to the stratosphere due to CFC's. This paper describes the characteristics of and data from the Halogen Occultation Experiment (HALOE) HF channel, including steps taken to validate the results. The on‐orbit precision of the HF measurements is shown to be better than 0.04 parts per billion by volume (ppbv) to 0.06 ppbv throughout the stratosphere. The estimated accuracy is 14% to 27% depending on altitude. The internal consistency of the HF measurements is excellent as judged by sunrise/sunset differences and comparison with HALOE CH4 distributions. The mean difference between HALOE HF and correlative balloon underflight measurements is <7% from 5 mbar to 50 mbar. Comparisons with the shuttle ATLAS 1 Atmospheric Trace Molecules Observed by Spectroscopy (ATMOS) data are not as good and there is a systematic difference between HALOE (smaller) and ATMOS (larger) ranging from 10% to 20% at altitudes above the 10‐mbar pressure level. Differences with ATMOS reach as much as 40% or more below the 10‐mbar level. The larger differences in this region are believed to be due to dynamical influences on HF coupled with wide separations in space and time between HALOE and ATMOS measurements. Analysis of HALOE HF pressure versus longitude cross sections shows that obtaining close space and time coincidence can be very important in comparing tracer distributions. Typical characteristics of a pressure versus latitude cross section and polar orthographic projection are also discussed. Comparisons with latitudinal distributions of tracer measurements from previous experiments show similar features like the tropical double minimum due to the semiannual oscillation. All comparisons and analyses conducted provide good confidence in the validity of the HALOE HF results.
Highlights
Introduction bandsDetails of the experiment,geographiccoverageof theThe HalogenOccultationExperiment(HALOE) was launched on boardthe Upper AtmosphereResearchSatelliteon September 12, 1991, into a 57ø inclination,585 km nearlycircularorbit
We recognizethatimportantcolumnamountvalues between --200 mbar and 50 mbar are not included, but we found occasional,rather small HALOE profile featuresof .0.2 ppbv maximum magnitude at the lowest altitudeswhich causedthe columnsumto changesignificantly
1 results measured at southern midlatitudes in March 1992 [Zander et al, 1994]
Summary
Typical HF modulation signal versus altitude (pressure) profilesfor low, middle,andhigh latitudesfor northernsummer andearly fall of 1992 are shownin Figure. The randomand systematicerror entriesin the table provide both estimated precision and accuracy information neededfor sciencestudies.The estimatedtotal error,obtainedby calculating the root-sum-squareof all individual errors, varies from a high of 27% at 100 mbar to as low as 14% at 5 mbar. These error estimates were obtained by calculating a signal profile based on realistic temperature-pressureH, F, CH4, and H20 profiles and the forward radiancecalculationmodel usedin the retrieval algorithm. The instrument noise used in the simulations was obtained from statisticalanalysisof exoatmospheridcata. It includestherefore digitization noise as well as detectorand electronicsnoise.
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