Discovery of a water vapor layer in the Arctic summer mesosphere: Implications for polar mesospheric clouds

Abstract

Abstract. We report the discovery of a layer of enhanced water vapor in the Arctic summer mesosphere that was made utilizing two new techniques for remotely determining water vapor abundances. The first utilizes Middle Atmosphere High Resolution Spectrograph Investigation (MAHRSI) OH measurements as a proxy for water vapor. The second is a reanalysis of Halogen Occultation Experiment (HALOE) water vapor data with a technique to simultaneously determine polar mesospheric cloud (PMC) ice particle extinction along with the water vapor abundance. These results reveal a narrow layer of enhanced water vapor centered between 82-84 km altitude and coincident with PMCs, that exhibits water vapor mixing ratios of 10-15 ppmv. This indicates that a higher degree of supersaturation is present in the PMC region, and that PMCs are thus more efficient at sequestering total water (both ice particles and vapor) within the layer, than previously believed.

Retrieval of water vapor profile in the mesosphere from satellite ozone and hydroxyl measurements by the basic dynamic model of mesospheric photochemical system

“…4 we present for comparison two vertical profiles of water vapour concentration in mesosphere measured by HALOE (v. 19) on 3 and 22 August 1997. Moreover, these maxima are also observed in the HALOE data measured in July-August at 65-70 • N (McHugh et al, 2003;Hervig et al, 2003) sedimentation and evaporation of particles of mesospheric clouds in the summer time at mesopause heights (Summers et al, 2001;Von Zahn and Berger, 2003). A possible cause of the second maximum of H 2 O concentration (at 73-75 km) may be heterogeneous reactions of H 2 O molecule formation on the surface of meteorite dust hypothesized by Summers and Siskind (1999).…”

“…Relative value of this difference (OH FIRS -OH MAHRSI )/OH MAHRSI ) grows with increasing height and amounts to about 33% already at 50 km. Note also that the value of OH FIRS ≈1.76·10 7 cm −3 at 50 km corresponds almost exactly to the model value of the OH concentration at the same height, which was calculated by Summers et al (2001) using the photochemical model with account for the distribution of H 2 O concentration from HALOE and, as opined by Sum- To conclude, we note that the proposed method of water vapour retrieval in mesosphere implies that the magnitude of this parameter at specific altitude weakly changes within several hours (4-7 h). This supposition may be violated in some cases, for example, near the boundary of a polar vortex where water vapour concentration has an appreciable meridional gradient and gravity waves impact the boundary (Lossow et al, 2009).…”

“…It may be conjectured that real values of constants of photochemical reactions differ strongly from the values recommended by JPL which we use in our research. Summers et al (2001) showed that OH concentrations measured within the framework of MAHRSI at 69-71 • N in the 50-79 km range of heights proved to be appreciably less (up to 50-60% less) than those calculated by the photochemical model with allowance for the dis- tribution of H 2 O concentration from HALOE. According to Summers et al (2001) the cause of this discrepancy is the overestimated (by 50%) standard JPL value of constant of the reaction O+HO 2 →O 2 +OH.…”

“…Summers et al (2001) showed that OH concentrations measured within the framework of MAHRSI at 69-71 • N in the 50-79 km range of heights proved to be appreciably less (up to 50-60% less) than those calculated by the photochemical model with allowance for the dis- tribution of H 2 O concentration from HALOE. According to Summers et al (2001) the cause of this discrepancy is the overestimated (by 50%) standard JPL value of constant of the reaction O+HO 2 →O 2 +OH. Figure 6 demonstrates the distribution of H 2 O concentration which we retrieved by the CRISTA-MAHRSI data same as in Fig.…”

“…The used data of OH concentration measurements at the heights of 50-70 km may be underestimated. In other words, the discrepancy noted by Summers et al (2001) between the model and measured concentrations of OH may be due to unrecorded error of MAHRSI measurements. This possibility is pointed to indirectly by data of simultaneous balloon-borne measurements of vertical distributions of OH, HO 2 , O 3 and H 2 O at 69 • N made by means of FIRS-2 at the heights of 30-50 km (Jucks et al, 1998) the same year as the MAHRSI campaign.…”