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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2010.06.035 Byline: R. de Kok (a), P.G.J. Irwin (b), N.A. Teanby (b) Keywords: Titan; Atmospheres, Composition; Infrared observations Abstract: We use Cassini far-infrared limb and nadir spectra, together with recent Huygens results, to shed new light on the controversial far-infrared opacity sources in Titan's troposphere. Although a global cloud of large CH.sub.4 ice particles around an altitude of 30km, together with an increase in tropospheric haze opacity with respect to the stratosphere, can fit nadir and limb spectra well, this cloud does not seem consistent with shortwave measurements of Titan. Instead, the N.sub.2-CH.sub.4 collision-induced absorption coefficients are probably underestimated by at least 50% for low temperatures. Author Affiliation: (a) SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands (b) Atmospheric, Oceanic & Planetary Physics, Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK Article History: Received 18 February 2010; Revised 12 June 2010; Accepted 23 June 2010

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2010.03.017 Byline: P.G.J. Irwin (a), N.A. Teanby (a), G.R. Davis (b) Keywords: Spectroscopy; Uranus, Atmosphere; Neptune, Atmosphere; Infrared observations Abstract: Long-slit spectroscopy observations of Uranus by the United Kingdom InfraRed Telescope UIST instrument in 2006, 2007 and 2008 have been used to monitor the change in Uranus' vertical and latitudinal cloud structure through the planet's Northern Spring Equinox in December 2007. These spectra were analysed and presented by Irwin et al. (Irwin, P.G.J., Teanby, N.A., Davis, G.R. [2009]. Icarus 203, 287-302), but since publication, a new set of methane absorption data has become available (Karkoschka, E., Tomasko, M. [2010]. Methane absorption coefficients for the jovian planets from laboratory, Huygens, and HST data. Icarus 205, 674-694.), which appears to be more reliable at the cold temperatures and high pressures of Uranus' deep atmosphere. We have fitted k-coefficients to these new methane absorption data and we find that although the latitudinal variation and inter-annual changes reported by Irwin et al. (2009) stand, the new k-data place the main cloud deck at lower pressures (2-3bars) than derived previously in the H-band of [approximately equal to]3-4bars and [approximately equal to]3bars compared with [approximately equal to]6bars in the J-band. Indeed, we find that using the new k-data it is possible to reproduce satisfactorily the entire observed centre-of-disc Uranus spectrum from 1 to 1.75[mu]m with a single cloud at 2-3bars provided that we make the particles more back-scattering at wavelengths less than 1.2[mu]m by, for example, increasing the assumed single-scattering albedo from 0.75 (assumed in the J and H-bands) to near 1.0. In addition, we find that using a deep methane mole fraction of 4% in combination with the associated warm 'F' temperature profile of Lindal et al. (Lindal, G.F., Lyons, J.R., Sweetnam, D.N., Eshleman, V.R., Hinson, D.P. [1987]. J. Geophys. Res. 92, 14987-15001), the retrieved cloud deck using the new (Karkoschka and Tomasko, 2010) methane absorption data moves to between 1 and 2bars. The same methane absorption data and retrieval algorithm were applied to observations of Neptune made during the same programme and we find that we can again fit the entire 1-1.75[mu]m centre-of-disc spectrum with a single cloud model, providing that we make the stratospheric haze particles (of much greater opacity than for Uranus) conservatively scattering (i.e. I =1) and we also make the deeper cloud particles, again at around the 2bar level more reflective for wavelengths less than 1.2[mu]m. Hence, apart from the increased opacity of stratospheric hazes in Neptune's atmosphere, the deeper cloud structure and cloud composition of Uranus and Neptune would appear to be very similar. Author Affiliation: (a) Atmospheric, Oceanic, and Planetary Physics, Department of Physics, University of Oxford, Clarendon Laboratory, Parks Rd., Oxford OX1 3PU, United Kingdom (b) Joint Astronomy Centre, 660 N. A'ohoku Place, Hilo, HI 96720, United States Article History: Received 29 September 2009; Revised 12 March 2010; Accepted 15 March 2010

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.05.003 Byline: P.G.J. Irwin (a), N.A. Teanby (a), G.R. Davis (b) Keywords: Spectroscopy; Uranus; Atmosphere; Infrared observations Abstract: Long-slit spectroscopy observations of Uranus by the United Kingdom Infrared Telescope UIST instrument in 2006, 2007 and 2008 have been used to monitor the change in Uranus' vertical and latitudinal cloud structure through the planet's northern spring equinox in December 2007. The observed reflectance spectra in the Long J (1.17-1.31[mu]m) and H (1.45-1.65[mu]m) bands, obtained with the slit aligned along Uranus' central meridian, have been fitted with an optimal estimation retrieval model to determine the vertical cloud profile from 0.1 to 6-8bar over a wide range of latitudes. Context images in a number of spectral bands were used to discriminate general zonal cloud structural changes from passing discrete clouds. From 2006 to 2007 reflection from deep clouds at pressures between 2 and 6-8bar increased at all latitudes, although there is some systematic uncertainty in the absolute pressure levels resulting from extrapolating the methane coefficients of Irwin et al. (Irwin, P.G.J., Sromovsky, L.A., Strong, E.K., Sihra, K., Teanby, N.A., Bowles, N., Calcutt, S.B., Remedios, J.J. [2006] Icarus, 181, 309-319) at pressures greater than 1bar, as noted by Tomasko et al. and Karkoschka and Tomasko (Tomasko, M.G., Bezard, B., Doose, L., Engel, S., Karkoschka, E. [2008] Planet. Space Sci., 56, 624-647; Karkoschka, E., Tomasko, M. [2009] Icarus). However, from 2007 to 2008 reflection from these clouds throughout the southern hemisphere and from both northern and southern mid-latitudes (30[degrees] N,S) diminished. As a result, the southern polar collar at 45[degrees]S has diminished in brightness relative to mid-latitudes, a similar collar at 45[degrees]N has become more prominent (e.g. Rages, K.A., Hammel, H.B., Sromovsky, L. [2007] Bull. Am. Astron. Soc., 39, 425; Sromovsky, L.A., Fry, P.M., Ahue, W.M., Hammel, H.B., de Pater, I., Rages, K.A., Showalter, M.R., van Dam, M.A. [2008] vol. 40 of AAS/Division for Planetary Sciences Meeting Abstracts, pp. 488-489; Sromovsky, L.A., Ahue, W.K.M., Fry, P.M., Hammel, H.B., de Pater, I., Rages, K.A., Showalter, M.R. [2009] Icarus), and the lowering reflectivity from mid-latitudes has left a noticeable brighter cloud zone at the equator (e.g. Sromovsky, L.A., Fry, P.M. [2007] Icarus, 192, 527-557;Karkoschka, E., Tomasko, M. [2009] Icarus). For such substantial cloud changes to have occurred in just two years suggests that the circulation of Uranus' atmosphere is much more vigorous and/or efficient than is commonly thought. The composition of the main observed cloud decks between 2 and 6-8bar is unclear, but the absence of the expected methane cloud at 1.2-1.3bar (Lindal, G.F., Lyons, J.R., Sweetnam, D.N., Eshleman, V.R., Hinson, D.P. [1987] J. Geophys. Res., 92, 14987-15001) is striking (as previously noted by, among others, Sromovsky, L.A., Irwin, P.G.J., Fry, P.M. [2006] Icarus, 182, 577-593; Sromovsky, L.A., Fry, P.M. [2007] Icarus, 192, 527-557; Sromovsky, L.A., Fry, P.M. [2008] Icarus, 193, 252-266; Karkoschka, E., Tomasko, M. [2009] Icarus) and suggests that cloud particles may be considerably different from pure condensates and may be linked with stratospheric haze particles drizzling down from above, or that tropospheric hazes are generated near the methane condensation level and then drizzle down to deep pressures as suggested by Karkoschka and Tomasko (Karkoschka, E., Tomasko, M. [2009] Icarus). The retrieved cloud structures were also tested for different assumptions of the deep methane mole fraction, which Karkoschka and Tomasko (Karkoschka, E., Tomasko, M. [2009] Icarus) find may vary from [approximately equal to]1-2% in polar regions to perhaps as much as 4% equatorwards of 45[degrees]N,S. We found that such variations did not significantly affect our conclusions. Author Affiliation: (a) Atmospheric, Oceanic, and Planetary Physics, Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom (b) Joint Astronomy Centre, 660 N. A'ohoku Place, Hilo, HI 96720, USA Article History: Received 21 January 2009; Revised 27 April 2009; Accepted 3 May 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2008.05.024 Byline: R. de Kok, P.G.J. Irwin, N.A. Teanby Keywords: Titan; Atmospheres; composition; Infrared observations Abstract: In Titan's north polar region stratospheric clouds are expected to form due to a combination of low temperatures and downward motion of volatile-enriched air. Here we investigate possible sources of stratospheric clouds at Titan's pole using data from the Cassini Composite Infrared Spectrometer and a simple condensation model. An upper limit for C.sub.4N.sub.2 gas was determined to be 9x10.sup.-9, which is less than required to make the C.sub.4N.sub.2 cloud at the Voyager epoch. Hence, the presence of this cloud after equinox remains a mystery. The largest cloud seen in far-infrared spectra has a feature around 220 cm.sup.-1 and is located around an altitude of 140 km. The upper limit for propionitrile (C.sub.2H.sub.5CN) gas shows that the feature around 220 cm.sup.-1 is probably not due to pure propionitrile ice. Instead, our model calculations show that HCN should cause by far the largest cloud around 140 km. We therefore propose that HCN ice plays an important role in the formation of the massive polar cloud, because of the unavailability of sufficient condensable gas other than HCN to produce a strong enough condensate feature. However, the signature at 220 cm.sup.-1 is not consistent with that of pure HCN ice at 172 cm.sup.-1 and mixing of HCN ice with other ices, or chemical alteration of HCN ice might mask the HCN ice signature. Author Affiliation: Atmospheric, Oceanic and Planetary Physics, Department of Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford, OX1 3PU, UK Article History: Received 26 February 2008; Revised 12 May 2008

Abstract: Since the 1970s, it has been predicted that both CO2 and H2O clouds can form in the Martian atmosphere, and many remote-sounding instruments have directly observed layers of extinction asserted to be clouds composed of either CO2 or H2O ice on Mars. The Mars Climate Sounder, onboard the Mars Reconnaissance Orbiter (MRO/MCS), entered orbit around Mars in 2006, and has been providing near-continuous coverage of the full planet since, at wavelengths from visible through to the mid-infrared, primarily in limb-viewing geometry, making it a suitable candidate to study the parameters of these clouds. In this work, the multiple scattering radiative-transfer tool NemesisMCS has been used to create a large dataset of simulations of CO2 and H2O clouds on Mars as would be measured by MRO/MCS, using a range of atmospheric conditions as well as cloud parameters derived from literature suitable for upper atmospheric clouds, and building specifically on the work of Sefton-Nash et al. (2013). This ensemble of simulations has been used to characterise the spectral signature of plausible CO2 and H2O clouds, as well as to assess the suitability of MRO/MCS to observe, to differentiate between, and to derive properties of such clouds. It has been found, given the noise levels expected for MRO/MCS and the range of atmospheric and cloud parameters sampled in this study, that radiance signals introduced by upper atmospheric clouds having nadir optical depths greater than about 10−5 should be distinguishable, with . This corresponds to specific concentrations greater than about 105 particles/g, particle radii greater than around , and cloud depths greater than about 2km. MRO/MCS measurements should be able to be used with confidence to differentiate between upper atmospheric cloud and dust in the lower atmosphere, and clear conditions, with high success ( ). Lower reliability classification is accomplished for CO2 clouds, with only 60% being correctly identified as CO2, and the remainder classified instead as H2O cloud, in the case of optical depths in the expected range for upper atmospheric cloudswhich are detectable by MRO/MCS, although this result is highly dependent upon the sampled selection of optically thin and thick clouds and the atmospheric model employed. Although almost all the H2O clouds are correctly identified, the fact that such a large proportion of CO2 clouds are misclassified as H2O clouds shows that the spectral information alone from MRO/MCS is insufficient to differentiate between CO2 and H2O clouds when optically thin—but detectable—clouds are included in the analysis. Using a simple look-up table (LUT) scheme and simulated data, retrieval of properties of upper atmospheric clouds of sufficient opacity is possible, with preliminary estimates indicating that H2O cloud and dust parameters can be correctly reproduced between 48% and 100% of the time, and between 18% and 92% of the time for CO2 cloud test cases, although it must be noted that these values must be taken as a qualitative measure which does not capture the full range of atmospheric and cloud conditions on Mars which would be present in real MRO/MCS data. Furthermore, because of the optical properties of H2O and CO2, on a like-with-like selection, the H2O clouds always produce greater perturbations in radiance, thus biasing results to a higher success rate for H2O cloud retrievals. Application of the method to MRO/MCS data with a full-optimal estimation retrieval tool such as NemesisMCS will be the topic of a future study. [Copyright &y& Elsevier]

Abstract: Mesospheric clouds have been previously observed on Mars in a variety of datasets. However, because the clouds are optically thin and most missions have performed surface-focussed nadir sounding, geographic and seasonal coverage is sparse. We present new detections of mesospheric clouds using a limb spectra dataset with global coverage acquired by NASA’s Mars Climate Sounder (MCS) aboard Mars Reconnaissance Orbiter. Mesospheric aerosol layers, which can be CO2 ice, water ice or dust clouds, cause high radiances in limb spectra, either by thermal emission or scattering of sunlight. We employ an object recognition and classification algorithm to identify and map aerosol layers in limb spectra acquired between December 2006 and April 2011, covering more than two Mars years. We use data from MCS band A4, to show thermal signatures of day and nightside features, and A6, which is sensitive to short wave IR and visible daytime features only. This large dataset provides several thousand detections of mesospheric clouds, more than an order of magnitude more than in previous studies. Our results show that aerosol layers tend to occur in two distinct regimes. They form in equatorial regions (30°S–30°N) during the aphelion season/northern hemisphere summer (L s <150°), which is in agreement with previous published observations of mesospheric clouds. During perihelion/dust storm season (L s >150°) a greater number of features are observed and are distributed in two mid-latitude bands, with a southern hemisphere bias. We observe temporal and longitudinal clustering of cloud occurrence, which we suggest is consistent with a formation mechanism dictated by interaction of broad temperature regimes imposed by global circulation and the propagation to the mesosphere of small-scale dynamics such as gravity waves and thermal tides. Using calculated frost point temperatures and a parameterization based on synthetic spectra we find that aphelion clouds are present in generally cooler conditions and are spectrally more consistent with H2O or CO2 ice. A significant fraction has nearby temperature retrievals that are within a few degrees of the CO2 frost point, indicating a CO2 composition for those clouds. Perihelion season clouds are spectrally most similar to H2O ice and dust aerosols, consistent with temperature retrievals near to the clouds that are 30–80K above the CO2 frost point. [Copyright &y& Elsevier]

Abstract: Near-infrared observations of Uranus were made in October/November 2010 with the Gemini-North telescope in Hawaii, using NIFS, an integral field spectrograph, and the NIRI instrument in imaging mode. Observations were acquired using adaptive optics and have a spatial resolution of approximately 0.1–0.2″. The observed spectra along Uranus’ central meridian were analysed using a multiple-scattering retrieval algorithm to infer the vertical/latitudinal variation in cloud optical depth, which we compare with previous observations made by Gemini-North/NIFS in 2009 and UKIRT/UIST observations made between 2006 and 2008. Assuming a continuous distribution of small particles (r ∼1μm, and refractive index of 1.4+0i) with the single scattering albedo set to 0.75 and using a Henyey–Greenstein phase function with asymmetry parameter set to 0.7 at all wavelengths and latitudes, the retrieved cloud density profiles show that the north polar zone at 45°N has continued to steadily brighten while the south polar zone at 45°S has continued to fade. As with our previous analyses we find that, assuming that the methane vertical profile is the same at all latitudes, the clouds forming these polar zones at 45°N and 45°S lie at slightly lower pressures than the clouds at more equatorial latitudes. However, we also find that the Gemini data can be reproduced by assuming that the main cloud remains fixed at ∼2bar at all latitudes and adjusting the relative humidity of methane instead. In this case we find that the deep cloud is still more opaque at the equator and at the zones at 45°N and 45°S and shows the same seasonal trends as when the methane humidity remain fixed. However, with this approach the relative humidity of methane is seen to rise sharply from approximately 20% at polar latitudes to values closer to 80% for latitudes equatorward of 45°S and 45°N, consistent with the analysis of 2002 HST observations by Karkoschka and Tomasko (Karkoschka, E., Tomasko, M. [2009]. Icarus 202, 287–302), with a possible indication of seasonal variability. Overall, Uranus appeared to be less convectively active in 2010 than in the previous 4years, supporting the conclusion that now the northern spring equinox (which occurred in 2007) has passed, the atmosphere is settling back into the more quiescent state seen by Voyager 2 in 1986. [Copyright &y& Elsevier]

Abstract: Observations of Neptune were made in September 2009 with the Gemini-North Telescope in Hawaii, using the NIFS instrument in the H-band covering the wavelength range 1.477–1.803μm. Observations were acquired in adaptive optics mode and have a spatial resolution of approximately 0.15–0.25″. The observations were analysed with a multiple-scattering retrieval algorithm to determine the opacity of clouds at different levels in Neptune’s atmosphere. We find that the observed spectra at all locations are very well fit with a model that has two thin cloud layers, one at a pressure level of ∼2bar all over the planet and an upper cloud whose pressure level varies from 0.02 to 0.08bar in the bright mid-latitude region at 20–40°S to as deep as 0.2bar near the equator. The opacity of the upper cloud is found to vary greatly with position, but the opacity of the lower cloud deck appears remarkably uniform, except for localised bright spots near 60°S and a possible slight clearing near the equator. A limb-darkening analysis of the observations suggests that the single-scattering albedo of the upper cloud particles varies from ∼0.4 in regions of low overall albedo to close to 1.0 in bright regions, while the lower cloud is consistent with particles that have a single-scattering albedo of ∼0.75 at this wavelength, similar to the value determined for the main cloud deck in Uranus’ atmosphere. The Henyey-Greenstein scattering particle asymmetry of particles in the upper cloud deck are found to be in the range g ∼0.6–0.7 (i.e. reasonably strongly forward scattering). Numerous bright clouds are seen near Neptune’s south pole at a range of pressure levels and at latitudes between 60 and 70°S. Discrete clouds were seen at the pressure level of the main cloud deck (∼2bar) at 60°S on three of the six nights observed. Assuming they are the same feature we estimate the rotation rate at this latitude and pressure to be 13.2±0.1h. However, the observations are not entirely consistent with a single non-evolving cloud feature, which suggests that the cloud opacity or albedo may vary very rapidly at this level at a rate not seen in any other giant-planet atmosphere. [Copyright &y& Elsevier]

Abstract: Observations of Uranus were made in September 2009 with the Gemini-North telescope in Hawaii, using both the NIFS and NIRI instruments. Observations were acquired in Adaptive Optics mode and have a spatial resolution of approximately 0.1″. NIRI images were recorded with three spectral filters to constrain the overall appearance of the planet: J, H-continuum and CH4(long), and long slit spectroscopy measurements were also made (1.49–1.79μm) with the entrance slit aligned on Uranus’ central meridian. To acquire spectra from other points on the planet, the NIFS instrument was used and its 3″×3″ field of view stepped across Uranus’ disc. These observations were combined to yield complete images of Uranus at 2040 wavelengths between 1.476 and 1.803μm. The observed spectra along Uranus central meridian were analysed with the NEMESIS retrieval tool and used to infer the vertical/latitudinal variation in cloud optical depth. We find that the 2009 Gemini data perfectly complement our observations/conclusions from UKIRT/UIST observations made in 2006–2008 and show that the north polar zone at 45°N has continued to steadily brighten while that at 45°S has continued to fade. The improved spatial resolution of the Gemini observations compared with the non-AO UKIRT/UIST data removes some of the earlier ambiguities with our previous analyses and shows that the opacity of clouds deeper than the 2-bar level does indeed diminish towards the poles and also reveals a darkening of the deeper cloud deck near the equator, perhaps coinciding with a region of subduction. We find that the clouds at 45°N,S lie at slightly lower pressures than the clouds at more equatorial latitudes, which suggests that they might possibly be composed of a different condensate, presumably CH4 ice, rather than H2S or NH3 ice, which is assumed for the deeper cloud. In addition, analysis of the centre-to-limb curves of both the Gemini/NIFS and earlier UKIRT/UIST IFU observations shows that the main cloud deck has a well-defined top, and also allows us to better constrain the particle scattering properties. Overall, Uranus appeared to be less convectively active in 2009 than in the previous 3years, which suggests that now the northern spring equinox (which occurred in 2007) is passed the atmosphere is settling back into the quiescent state seen by Voyager 2 in 1986. However, a number of discrete clouds were still observed, with one at 15°N found to lie near the 500 mb level, while another at 30°N, was seen to be much higher at near the 200 mb level. Such high clouds are assumed to be composed of CH4 ice. [Copyright &y& Elsevier]

We have developed a new retrieval approach to modelling near-infrared spectra of Uranus that represents a significant improvement over previous modelling methods. We reanalysed IRTF/SpeX observations of Uranus observed in 2009 covering the wavelength range 0.8–1.8 μm and reported by Tice et al. (Tice, D.S., Irwin, P.G.J., Fletcher, L.N., Teanby, N.A., Hurley, J., Orton, G.S., Davis, G.R. [2013]. Icarus 223, 684–698). By retrieving the imaginary refractive index spectra of cloud particles we are able to consistently define the real part of the refractive index spectra, through a Kramers–Kronig analysis, and thus determine self-consistent extinction cross-section, single-scattering and phase-function spectra for the clouds and hazes in Uranus’ atmosphere. We tested two different cloud-modelling schemes used in conjunction with the temperature/methane profile of Baines et al. (Baines, K.H., Mickelson, M.E., Larson, L.E., Ferguson, D.W. [1995]. Icarus 114, 328–340), a reanalysis of the Voyager-2 radio-occultation observations performed by Sromovsky, Fry and Kim (Sromovsky, L.A., Fry, P.M., Kim, J.H. [2011]. Icarus 215, 292–312), and a recent determination from Spitzer (Orton, G.S., Fletcher, L.N., Moses, J.I., Mainzer, A.K., Hines, D., Hammel, H.B., Martin-Torres, F.J., Burgdorf, M., Merlet, C., Line, M.R. [2014]. Icarus 243, 494–513). We find that both cloud-modelling schemes represent the observed centre-of-disc spectrum of Uranus well, and both require similar cloud scattering properties of the main cloud residing at ∼2 bars. However, a modified version of the Sromovsky, Fry and Kim (2011) model, with revised spectral properties of the lowest cloud layer, fits slightly better at shorter wavelengths and is more consistent with the expected vertical position of Uranus’ methane cloud. We find that the bulk of the reflected radiance from Uranus arises from a thick cloud at approximately the 2 bar level, composed of particles that are significantly more absorbing at wavelengths λ > 1.0 μm than they are at shorter wavelengths λ < 1.0 μm. This spectral information provides a possible constraint on the identity of the main particle type, although we find that the scattering properties required are not consistent with any of the available laboratory data for pure NH 3 , NH 4 SH, or CH 4 ice (all suspected of condensing in the upper troposphere). It is possible that the observed clouds are mixtures of tropospheric condensate mixed with photochemical products diffusing down from above, which masks their pure scattering features. Because there is no available laboratory data for pure H 2 S or PH 3 ice (both of which might be present as well), they cannot be excluded as the cloud-forming species. We note, however, that their absorptive properties would have to be two orders of magnitude greater than the other measured ices at wavelengths greater than 1 μm to be consistent with our retrieval, which suggests that mixing with photochemical products may still be important. [ABSTRACT FROM AUTHOR]

Highlights: [•] Revised WKMC-80K methane line data give very good fit to Neptune H-band spectra. [•] Reflectivity of particles in main cloud deck is found to decrease with wavelength from 1.4 to 1.6μm. [•] Neptune’s CH3D/CH4 ratio is determined to be . [•] The abundance of CO at the cloud tops (2–3bars) is found to be much less than in the stratosphere. [ABSTRACT FROM AUTHOR]