Implications of enhanced mesospheric water vapor observed by HALOE

Abstract

Abstract. Recently reprocessed water vapor data from theHalogen Occultation Experiment (HALOE) on the UARS satellite show significant deviations from the expected constant value of 2'CH4 + HI20. An unusual enhancement in the I-I20 is seen from 65-70 km which exceeds the stratospheric the value of 2'CH4 + I-I20 by 0.6-0.8 ppmv. This is inconsistent with the conventional view of transport of I-I20 and CH4 up from the lower stratosphere and photodissociation in the mesosphere and suggests the presence of another source of I-I2 O. We re-evaluate the hypothesis that there is an extraterrestrial source of water deposited at mesospheric altitudes. The HALOE data above 60 km provide stringent new constraints on the magnitude and altitude of such a source, but cannot rule out the possibility of a small contribution in the middle mesosphere.

Measurements of middle atmospheric water vapor from low latitudes and midlatitudes in the northern hemisphere, 1995–1998

“…The notch in the unconvolved HALOE v18 profiles near 60 km is a prominent feature in Figures 7a and 7b. The observed decrease in water vapor mixing ratio retrieved by HALOE at this altitude is in disagreement with presently understood chemistry [Siskind and Summers, 1998]. This notch is not present in the convolved HALOE retrievals, because the WVMS retrievals do not have the resolution required to resolve such a feature.…”

An “island” in the stratosphere – on the enhanced annual variation of water vapour in the middle and upper stratosphere in the southern tropics and subtropics

“…Other instances can be found, for example, in the work of Holton and Choi (1988) or Randel et al (1998), which show this feature in methane. Since H 2 O + 2 · CH 4 is approximately a conserved parameter in the stratosphere and lower mesosphere (Le Texier et al, 1988;Siskind and Summers, 1998) the structure and variability of methane and water vapour are tightly linked with each other. All these publications have, however, a much wider scientific focus: variability in general and atmospheric transport.…”

Evidence for slowdown in stratospheric ozone loss: First stage of ozone recovery

“…We expect to see signs of ozone recovery first in the 40-km region [Jucks et al, 1996]; however, because of interactions with increasing greenhouse gases, decreasing temperature, and circulation changes, these climate changes can mask an ozone recovery from chlorine-catalyzed loss [Shindell et al, 1998]. Furthermore, detecting signs of ozone recovery first in the 40-km region is extremely important for confirming our understanding of ozone chemistry in the upper stratosphere, a research area with significant heritage in measurements, modeling, and laboratory investigations [Chen et al, 1997;Crutzen et al, 1995;Dessler et al, 1998;Eluszkiewicz and Allen, 1993;Froidevaux et al, 1985;Grooß et al, 1999;Jackman et al, 1996;Jucks et al, 1996;Kegley-Owen et al, 1999;Khosravi et al, 1998;Lipson et al, 1999;Michelsen et al, 1994;Minschwaner and Siskind, 1993;Natarajan and Callis, 1991;Randel et al, 1999;Reinsel et al, 1999;Russell et al, 1996b;Siskind et al, 1995;Siskind and Summers, 1998;Stolarski et al, 1992;Stolarski and Douglass, 1986;Summers et al, 1997;Viggiano et al, 1995;Waters et al, 1996;Wennberg et al, 1994] and in the effects on ground-level ultraviolet radiation [McKenzie et al, 1999;Rozema et al, 2002]. Most recently, for example, Shindell and Grewe [2002] show that the 40-km region is not only the optimum location to identify recovery but also is the ideal location to ascribe attribution due to CFC reductions and complicating greenhouse gas effects [Shindell et al, 1999;Shindell, 2001].…”