Mountain wave PSC dynamics and microphysics from ground-based lidar measurements and meteorological modeling

Abstract

Abstract. The day-long observation of a polar stratospheric cloud (PSC) by two co-located ground-based lidars at the Swedish research facility Esrange (67.9 • N, 21.1 • E) on 16 January 1997 is analyzed in terms of PSC dynamics and microphysics. Mesoscale modeling is utilized to simulate the meteorological setting of the lidar measurements. Microphysical properties of the PSC particles are retrieved by comparing the measured particle depolarization ratio and the PSC-averaged lidar ratio with theoretical optical data derived for different particle shapes. In the morning, nitric acid trihydrate (NAT) particles and then increasingly coexisting liquid ternary aerosol (LTA) were detected as outflow from a mountain wave-induced ice PSC upwind Esrange. The NAT PSC is in good agreement with simulations for irregularshaped particles with length-to-diameter ratios between 0.75 and 1.25, maximum dimensions from 0.7 to 0.9 µm, and a number density from 8 to 12 cm −3 and the coexisting LTA droplets had diameters from 0.7 to 0.9 µm, a refractive index of 1.39 and a number density from 7 to 11 cm −3 . The total amount of condensed HNO 3 was in the range of 8-12 ppbv. The data provide further observational evidence that NAT forms via deposition nucleation on ice particles as a number of recently published papers suggest. By early afternoon the mountain-wave ice PSC expanded above the lidar site. Its optical data indicate a decrease in minimum particle size from 3 to 1.9 µm with time. Later on, following the weakening of the mountain wave, wave-induced LTA was observed only. Our study demonstrates that ground-based lidar measurements of PSCs can be comprehensively interpreted if combined with mesoscale meteorological data.

A-train CALIOP and MLS observations of early winter Antarctic polar stratospheric clouds and nitric acid in 2008

“…There is no simple depolarization dependency on the particle shape (Liu and Mishchenko, 2001;Reichardt et al, 2002), and a variety of shapes are consistent with lidar observations (Reichardt et al, 2004). Particle shapes for NAT are likely to be physically more complex figures than spheroids or cylinders; however, these are commonly used for the interpretation of lidar measurements:…”

CALIPSO observations of wave‐induced PSCs with near‐unity optical depth over Antarctica in 2006–2007

“…Within cloudy lidar profiles, we looked for a 1‐km clear‐sky area (33 points) from the tropopause and up. If clear sky was not found below 28 km the profile was rejected; otherwise PSC extinction and optical depth τ were estimated by the difference in molecular and attenuated backscatter within the clear sky area ( Young [1995], also used by Reichardt et al [2004]). Multiple scattering effects should be negligible considering the low extinctions under consideration [ Chepfer et al , 1999]; these effects could be significant for highly opaque PSCs, but would lead to underestimated optical depths and would not change the conclusions.…”

“…Following Adriani et al [2004], δ > 0.3 should be indicative of solid cristalline composition; Reichardt et al [2004] report 56 < S < 135 for type I and 16 < S < 42 for ice‐based type II PSCs ( Platt et al [1999] report a 25–34 range for cirrus clouds). In the present case, high depolarization ratios (0.3 < δ < 0.55) and low lidar ratios (S ∼ 20, Figure 1c) are consistent with type II.…”

“… Höpfner et al [2001], through the analysis of the solar absorption spectrum, found optical depths 0.25–0.8 in the infrared (10.6–12.5 μ m) for a case study PSC over Sweden, a result difficult to extend to the visible domain. Regarding lidar observations, Reichardt et al [2004] derived optical depths as part of their analysis of mountain wave PSCs over Sweden, but were not presented in the text. Because of this lack of quantitative reference, the 2002 study of Arctic stratospheric components by Tabazadeh et al [2002] still refers to an optical depth range below 0.04 for PSCs, as documented by McCormick et al [1981].…”

Optical‐microphysical cirrus model

“…During January 1997 the GKSS Raman lidar [ Reichardt et al , 1996] was monitoring the winter atmosphere above the Esrange research station, Sweden (67.9°N, 21.1°E) in search for polar stratospheric clouds forming downwind the Scandinavian mountain ridge [e.g., Reichardt et al , 2004]. This campaign provided the opportunity to collect a multiparameter data set of Arctic cirrus clouds, with the initial intention to compare it to the observations of midlatitude cirrus clouds made at the home base of the instrument near Geesthacht, Germany (53.5°N, 10.5°E) [ Reichardt , 1999].…”