Geophysica Aircraft Research Articles

Nitric Acid Trihydrate (NAT) formation at low NAT supersaturation in Polar Stratospheric Clouds (PSCs)

Abstract. A PSC was detected on 6 February 2003 in the Arctic stratosphere by in-situ measurements onboard the high-altitude research aircraft Geophysica. Low number densities (~10-4cm-3) of small nitric acid (HNO3) containing particles (d<6µm) were observed at altitudes between 18 and 20km. Provided the temperatures remain below the NAT equilibrium temperature TNAT, these NAT particles have the potential to grow further and to remove HNO3 from the stratosphere, thereby enhancing polar ozone loss. Interestingly, the NAT particles formed in less than a day at temperatures just slightly below TNAT (T>TNAT-3.1K). This unique measurement of PSC formation at extremely low NAT saturation ratios (SNAT≤10) constrains current NAT nucleation theories. We suggest, that the NAT particles have formed heterogeneously, but for certain not on ice. Conversely, meteoritic particles may be favorable candidates for triggering NAT nucleation at the observed low number densities.

Polar stratospheric clouds observed during the Airborne Polar Experiment–Geophysica Aircraft in Antarctica (APE‐GAIA) campaign

In this work, observations of polar stratospheric clouds (PSC) carried out during one flight of the stratospheric research aircraft Geophysica deployed in the Airborne Polar Experiment–Geophysica Aircraft in Antarctica (APE‐GAIA) campaign in September–October 1999 are presented. An analysis of data from the two lidars and a backscatter sonde on board the Geophysica aircraft is presented, coupled with temperature measurements. The observations are analyzed with the aid of a mesoscale model to provide air mass thermal histories and a microphysical box model to simulate PSC formation. The results obtained from this comparison are discussed in view of the theories for PSC formation processes.

Observation of polar stratospheric clouds with the ABLE LIDAR during the APE-POLECAT flight of January 9, 1997

Observations of Polar Stratospheric Clouds (PSCs) were carried out with an airborne lidar on the stratospheric M55 Geophysica aircraft during a flight from Rovaniemi, Finland, on 9 January, 1997. The clouds were observed at the zenith, downwind from the Norwegian Alps: three PSCs, of somewhat different characteristics, were detected at heights between 23 and 28 km . In two of the clouds, different types of particles seem to coexist: echoes attributable to types I and II PSCs are found in different portions of the clouds. The formation of the PSCs is related to an orographic lee-wave, whose development was forecast by a mesoscale dynamical model used to plan the flight path. The largest observed PSC displays a complex structure, that appears to be influenced by waves of different wavelengths. In particular, lidar and in situ data suggest the presence of a wave having a relatively short length (about 18 km ) that overlaps on the main lee-wave. The short wavelength oscillation is thought to play a major role in the cloud development, determining the rapid formation and evaporation of particles and therefore the non-stationary character of the PSC.

In situ measurements of background aerosol and subvisible cirrus in the tropical tropopause region

In situ aerosol measurements were performed in the Indian Ocean Intertropical Convergence Zone (ITCZ) region during the Airborne Polar Experiment‐Third European Stratospheric Experiment on Ozone (APE‐THESEO) field campaign based in Mahé, Seychelles between 24 February and 6 March 1999. These are measurements of particle size distributions with a laser optical particle counter of the Forward Scattering Spectrometer Probe (FSSP)‐300 type operated on the Russian M‐55 high‐altitude research aircraft Geophysica in the tropical upper troposphere and lower stratosphere up to altitudes of 21 km. On 24 and 27 February 1999, ultrathin layers of cirrus clouds were penetrated by Geophysica directly beneath the tropical tropopause at 17 km pressure altitude and temperatures below 190 K. These layers also were concurrently observed by the Ozone Lidar Experiment (OLEX) lidar operating on the lower‐flying German DLR Falcon research aircraft. The encountered ultrathin subvisual cloud layers can be characterized as (1) horizontally extending over several hundred kilometers, (2) persisting for at least 3 hours (but most likely much longer), and (3) having geometrical thicknesses of 100–400 m. These cloud layers belong to the geometrically and optically thinnest ever observed. In situ particle size distributions covering diameters between 0.4 and 23 μm obtained from these layers are juxtaposed with those obtained inside cloud veils around cumulonimbus (Cb) anvils and also with background aerosol measurements in the vicinity of the clouds. A significant number of particles with size diameters around 10 μm were detected inside these ultrathin subvisible cloud layers. The cloud particle size distribution closely resembles a background aerosol onto which a modal peak between 2 and 17 μm is superimposed. Measurements of particles with sizes above 23 μm could not be obtained since no suitable instrument was available on Geophysica. During the flight of 6 March 1999, upper tropospheric and lower stratospheric background aerosol was measured in the latitude band between 4°S and 19°S latitude. The resulting particle number densities along the 56th meridian exhibit very little latitudinal variation. The concentrations for particles with sizes above 0.5 μm encountered under these background conditions varied between 0.1 and 0.3 particles/cm3 of air in altitudes between 17 and 21 km.

Off-axis measurements of atmospheric trace gases by use of an airborne ultraviolet-visible spectrometer.

An airborne UV-visible spectrometer, the Gas Analyzer Spectrometer Correlating Optical Differences, airborne version (GASCOD/A4pi) was successfully operated during the Airborne Polar Experiment, Geophysica Aircraft in Antarctica airborne campaign from Ushuaia (54 degrees 49' S, 68 degrees 18' W), Argentina in southern spring 1999. The instrument measured scattered solar radiation through three optical windows with a narrow field of view (FOV), one from the zenith, two from the horizontal, as well as actinic fluxes through 2pi FOV radiometric heads. Only a few airborne measurements of scattered solar radiation at different angles from the zenith are available in the literature. With our configuration we attempted to obtain the average line-of-sight concentrations of detectable trace gases. The retrieval method, based on differential optical absorption spectroscopy, is described and results for ozone are shown and compared with measurements from an in situ instrument as the first method of validation.

A Chemiluminescent Analyzer for Stratospheric Measurements of the Ozone Concentration (FOZAN)

Abstract Within the framework of the Airborne Polar Experiment, a new ozone analyzer based on chemiluminescent technology has been developed for high-altitude measurements. The instrument was tested on board the M-55 Geophysica aircraft during some flights over Italy, reaching an altitude of about 20 000 m and a temperature of about −75°C. This paper presents the chemiluminescent characteristics of the sensor, the electronic design of the instrument, and a comparison between the results obtained during a test flight with those derived from a contemporary balloon sounding. The instrumental performances of the analyzer were found to be suitable for stratospheric applications.

ABLE: Development of an Airborne Lidar

Abstract The acronym ABLE (Airborne Lidar Experiment) identifies a project to develop and fly an optical radar on a stratospheric platform for studies related to atmospheric radiation and composition. The prototype, ABLE 1, has been successfully flown on board the M55 Geophysica aircraft in the Arctic campaign of December 1996–January 1997 to observe stratospheric clouds and aerosol. The lidar, which runs automatically, has been installed in the unpressurized bay of the aircraft where the temperature approaches the low values of external air. The lidar transmitter is based on a Nd:YAG laser, with second and third harmonic outputs. The receiver consists of a 0.3-m Cassegrain telescope and several detection channels to look at different wavelengths and polarizations. A fluid circulation unit connected to the aircraft provides heating control. The instrument can point to the zenith or to the nadir. In the past campaign only λ = 532 nm was utilized: observations were carried out at two polarizations, pointing...