Properties of polar stratospheric clouds observed by ILAS in early 1997

Abstract

[1] The relative extinction coefficients for Arctic polar stratospheric clouds (PSCs) are determined using a transmittance-ratio technique from spectral data observed in early 1997 by the Improved Limb Atmospheric Spectrometer (ILAS). The observed relative extinction coefficients are compared with theoretical coefficients calculated by the Mie theory for single mode lognormal size distributions of PSCs. The observed PSCs are then classified into three types: nitric acid droplets (HNO 3 /H 2 O), and nitric acid trihydrate (NAT) solid particles in the form of a-NAT and b-NAT. However, the definitive detection of a-NAT is difficult due to uncertainties of atmospheric temperature measurements and laboratory determination of refractive indices.

Polar stratospheric cloud microphysics and chemistry

“…They validated their method using lidar observations that were coincident with POAM observations. Poole et al (2003), Lee et al (2003), and Kim et al (2006) have extended the use of this technique to the analysis of SAGE III measurements and ILAS-I/ILAS-II measurements, respectively. Relative extinction coefficients are calculated using adjacent transmittance profiles, one containing a PSC signature, the second containing none.…”

Characterization of stratospheric liquid ternary solution aerosol from broadband infrared extinction measurements

“…[30] The retrievals obtained by Lee et al [2003] corresponded to the best spectral fitting at 51.5% (Figure 10, left) and 56% (Figure 10, right) weights of nitric acid using the data of Norman et al [1999] for the refractive indices. However, both values obtained by Lee et al [2003] technique are larger than those predicted by the Carslaw model [Carslaw et al, 1995] at the typical atmospheric conditions specified in section 2.…”

“…[29] The retrievals of size parameters using both techniques are in good agreement, as seen in Figure 10 and Table 1. Although size positions of the maxima of the particle size distribution retrieved by the bicomponent approximation are somewhat larger than those obtained by Lee et al [2003], the mean sizes R a are in excellent agreement (Table 1 and insert in Figure 10, bottom).…”

“…With this approximation, we follow selection of the reference spectra described in previous section. The PSCs observed on 15 January 1997 (65.3°N, 17.4°E) and on 17 January 1997 (65.6°N, 32.0°E) were identified by Lee et al [2003] as mainly composed of supercooled binary solution at tangent heights h = 24–25 km and h = 23–24 km, respectively. This identification is based on the ratio technique aimed to extract the optical depth of pure PSC spectra using transmittance for both PSC T P (λ, h ) and adjacent background T B (λ, h ) occultation events.…”

“…Application of the bicomponent approximation and technique of Lee et al [2003] to the ILAS observations for two occultation events. (top) Absorption bands of O 3 and HNO 3 for a single 21‐km layer, (middle) spectral fitting of the relative extinction coefficient (solid circles) by applying the bicomponent approximation (shaded curves) and the ratio technique (solid curves), and (bottom) retrieved volume particle size distribution according to the bicomponent approximation (shaded curves) and the ratio technique (solid curves).…”