The MLS HCl Product
Basic Information
HCl in the stratosphere (from 15 to 50 km altitude) is a gas that results from the decomposition (by UV radiation) of tropospheric sources gases, mainly chlorofluorocarbons (CFCs). Most of the chlorine that is released from CFCs are stored in this HCl reservoir at high altitudes (near 50 km), and HCl in the upper stratosphere provides a measure of the total chlorine content of the atmosphere (an abundance close to 3.5 parts per billion by volume). The chemistry that leads to ozone depletion at high latitudes largely comes from the more reactive forms of gaseous chlorine (mainly as ClO or chlorine monoxide, also measured by MLS), which makes up all or a large fraction of the atmospheric chlorine content in the lower stratosphere (near 20 km altitude) during polar winter and spring. Some chlorine at high altitude (near 40 km) is also in the form of ClO, which participates in ozone depletion as well. HCl is converted to ClO at high altitude, mainly by reaction with the OH radical; methane (CH4) reacting with chlorine atoms reforms HCl. A steady-state balance in the concentrations of active and reservoir chlorine molecules is achieved. Chlorine nitrate (ClONO2) also plays a role as a temporary chlorine reservoir, usually with lower abundances than HCl. |
The HCl Molecule
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How it is part of MLS Science Objectives
One of the objectives for MLS and the Aura mission is to understand and
follow changes in the chemistry and atmospheric composition that can affect
stratospheric ozone. HCl in the upper stratosphere has now been decreasing
(since about the turn of the century), based on expectations from measurements
of CFCs at the ground as well as past satellite HCl data and column
HCl measurements from ground-based infrared data. MLS is observing the global
decrease in upper stratospheric HCl, which confirms that international
agreements to limit the production of CFCs is having an impact in the region
where ozone depletion has occurred, during the past two decades. In the lower stratosphere during
polar winter and spring, the MLS measurements of HCl and ClO provide important information
about the partitioning of chlorine products critical to ozone depletion.
How EOS MLS measures HCl
The standard product for HCl is taken from the 640 GHz (Core+R4A) retrieval. Simulations indicate excellent closure for HCl, typically to better than ~1%. Systematic biases (usually positive) tend to increase to 0.1 ppbv or more at the lowermost pressure (147 hPa); this can amount to more than 30% for the small abundances often found at this altitude. This, and the fact that the random error also increases significantly there leads us to be cautious about HCl below 100 hPa, except possibly at high latitudes where larger abundances can be found.
(map from 2005d264)
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HCl Information from the Spectroscopy Database
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Quick Product Information for data version v2.2
- Swath Name: HCl
- Vertical Resolution:
~3km lower stratosphere
4-6 km at 1hPa and higher
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- Useful Range: 100 - 0.15 hPa
- DAAC Short Name: ML2HCL
- Precision:
0.3-0.2 ppbv at 100-10 hPa
0.2-0.9 ppbv at 10-0.2 hPa
- Accuracy: 5-10% (height-dependent)
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The RMS scatter about the 'truth' (for noisy retrievals) is slightly (20%) lower than the estimated precision in the lower stratosphere and up to 50% lower in the lower mesosphere. Clouds tend to cause some (mostly positive) biases, but mainly at 147 hPa where the estimated precision is also increasing; therefore the effect on real data will not be obvious. Some profiles incur vertical oscillations at high latitudes, although this is usually within the estimated noise of the measurements.
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v2.2 HCl Averaging Kernel
colored lines are individual kernels; thick dashed line is full width at half maximum, thick solid is integrated kernel value
Publications related to the MLS HCl data product
2008
- Lary, D.J., O. Aulov, "Space-based measurements of HCl: Intercomparison and historical context", vol 113, pgs. D15S04, 2008. Reprint
- Froidevaux, L., Y.B. Jiang, A. Lambert, N.J. Livesey, W.G. Read, J.W. Waters, R.A. Fuller, T.P. Marcy, P.J. Popp, R.S. Gao, D.W. Fahey, K.W. Jucks, R.A. Stachnik, G.C. Toon, L.E. Christensen, C.R. Webster, P.F. Bernath, C.D. Boone, K.A. Walker, H.C. Pumphrey, R.S. Harwood, G.L. Manney, M.J. Schwartz, W.H. Daffer, B.J. Drouin, R.E. Cofield, D.T. Cuddy, R.F. Jarnot, B.W. Knosp, V.S. Perun, W.V. Snyder, P.C. Stek, R.P. Thurstans, P.A. Wagner, "Validation of Aura Microwave Limb Sounder HCl measurements", vol 113, 2008. Preprint
- Schoeberl, M.R., A.R. Douglass, P.A. Newman, L.R. Lait, D. Lary, J. Waters, N. Livesey, L. Froidevaux, A. Lambert, W. Read, M.J. Filipiak, H.C. Pumphrey, "QBO and Annual Cycle Variations in Tropical Lower Stratosphere Trace Gases from HALOE and Aura MLS Observations", vol 113, pgs. D05301, 2008. Reprint
- Santee, M.L., I.A. MacKenzie, G.L. Manney, M.P. Chipperfield, P.F. Bernath, K.A. Walker, C.D. Boone, L. Froidevaux, N.J. Livesey, J.W. Waters, "A study of stratospheric chlorine partitioning based on new", vol 113, 2008. Preprint
- Coffey, M.T., J.W. Hannigan, A. Goldman, D.E. Kinnison, J.C. Gille, J. Barnett, L. Froidevaux, A. Lambert, M.L. Santee, N.J. Livesey, B.M. Fisher, S.S. Kulawik, R. Beer, "Airborne Fourier transform spectrometer (FTS) observations in support of EOS Aura validation", 2008. Preprint
- Considine, D.B., M. Natarajan, T.D. Fairlie, G.S. Lingenfelser, R.B. Pierce, L. Froidevaux, A. Lambert, "Noncoincident validation of Aura MLS observations using the Langley Research Center Lagrangian chemistry and transport model", 2008. Preprint
2007
- Manney, G.L., W.H. Daffer, J.M. Zawodny, P.F. Bernath, K.W. Hoppel, K.A. Walker, B.W. Knosp, C. Boone, E.E. Remsberg, M.L. Santee, V. Lynn Harvey, S. Pawson, D.R. Jackson, L. Deaver, C.T. McElroy, C.A. McLinden, J.R. Drummond, H.C. Pumphrey, A. Lambert, M.J. Schwartz, L. Froidevaux, S. McLeod, L.L. Takacs, M.J. Suarez, C.R. Trepte, D.T. Cuddy, N.J. Livesey, R.S. Harwood, J.W. Waters, "Solar Occultation Satellite Data and Derived Meteorological Products: Sampling Issues and Comparisons with Aura MLS", vol 112, pgs. D24S50, 2007. Reprint
- Lary, D.J., D.W. Waugh, A.R. Douglass, R.S. Stolarski, P.A. Newman, H. Mussa, "Variations in Stratospheric Inorganic Chlorine Between 1991 and 2006", vol 34, pgs. L21811, 2007. Reprint
2006
- Froidevaux, L., N.J. Livesey, W.G. Read, Y.B. Jiang, C.J. Jimenez, M.J. Filipiak, M.J. Schwartz, M.L. Santee, H.C. Pumphrey, J.H. Jiang, D.L. Wu, G.L. Manney, B.J. Drouin, J.W. Waters, E.J. Fetzer, P.F. Bernath, C.D. Boone, K.A. Walker, K.W. Jucks, G.C. Toon, J.J. Margitan, B. Sen, C.R. Webster, L.E. Christensen, J.W. Elkins, E. Atlas, R.A. Lueb, R. Hendershot, "Early validation analyses of atmospheric profiles from EOS MLS on the Aura satellite", vol 44, num no. 5, 2006. Reprint
- Cofield, R.E., P.C. Stek, "Design and field-of-view calibration of 114-660 GHz optics of the Earth Observing System Microwave Limb Sounder", vol 44, num no. 5, pgs. 1166-1181, 2006. Reprint
- Froidevaux, L., N.J. Livesey, W.G. Read, R.J. Salawitch, J.W. Waters, B.J. Drouin, I.A. MacKenzie, H.C. Pumphrey, P. Bernath, C. Boone, R. Nassar, S. Montzka, J. Elkins, D. Cunnold, D. Waugh, "Temporal decrease in upper atmospheric chlorine", vol 33, pgs. L23812, 2006. Reprint Supplemental
- Schoeberl, M.R., S.R. Kawa, A.R. Douglass, T.J. McGee, E.V. Browell, J.W. Waters, N.J. Livesey, W.G. Read, L. Froidevaux, M.L. Santee, H.C. Pumphrey, L.R. Lait, L. Twigg, "Chemical Observations of a Polar Vortex Intrusion", vol 111, pgs. D20306, 2006. Reprint
- Hilsenrath, E., M.R. Schoeberl, A.R. Douglass, P.K. Bhartia, J. Barnett, R. Beer, J. Waters, M. Gunson, L. Froidevaux, J. Gille, P.F. Levelt, "Early Data from Aura and Continuity from UARS and TOMS", vol 125, pgs. 417-430, 2006. Reprint
2005
- Manney, G.L., M.L. Santee, N.J. Livesey, L. Froidevaux, W.G. Read, H.C. Pumphrey, J.W. Waters, S. Pawson, "EOS Microwave Limb Sounder Observations of the Antarctic Polar Vortex Breakup in 2004", vol 32, pgs. L12811, 2005. Reprint Summary
- Santee, M.L., G.L. Manney, N.J. Livesey, L. Froidevaux, H.C. Pumphrey, W.G. Read, M.J. Schwartz, J.W. Waters, "Polar processing and development of the 2004 Antarctic ozone hole: First results from Aura MLS", vol 32, pgs. L12817, 2005. Reprint Summary
2004
- Drouin, B.J., "Temperature Dependent Pressure Induced Lineshape of the HCl J = 1 <- 0 Rotational Transition in Nitrogen and Oxygen", vol 83, num Issues 3-4, pgs. 321-331, 2004. Reprint Summary
2003
- Muller, R., S. Tilmes, J-U. Groos, D.S. McKenna, M. Muller, U. Schmidt, G.C. Toon, R.A. Stachnik, J.J. Margitan, J.W. Elkins, J. Arvelius, J.M. Russell, "Chlorine activation and chemical loss deduced from HALOE and balloon measurements in the Arctic during the winter of 1999-2000", vol 108, num D5, pgs. 8302, 2003. Reprint
1999
- Stachnik, R.A., R.J. Salawitch, A. Engel, U. Schmidt, "Measurements of chlorine partitioning in the winter Arctic stratosphere", vol 26, pgs. 3093-3096, 1999. Reprint
1997
- Engel, A., U. Schmidt, R.A. Stachnik, "Partitioning Between Chlorine Reservoir Species Deduced from Observations in the Arctic Winter Stratosphere", vol 27, pgs. 107-126, 1997. Reprint
1992
- Stachnik, R.A., J.C. Hardy, J.A. Tarsala, J.W. Waters, N.R. Erickson, "Submillimeterwave heterodyne measurements of stratospheric ClO, HCl, O3, and HO2: First results", vol 19, pgs. 1931-1934, 1992. Reprint
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