Clouds in Antarctica are key elements that affect radiative forcing and thus Antarctic climate evolution. Although the vast majority of clouds are composed of ice crystals, a non-negligible fraction ...constitutes supercooled liquid water (SLW; water held in liquid form below 0 °C). Numerical weather prediction models have great difficulty in forecasting SLW clouds over Antarctica, favouring ice at the expense of liquid water and therefore incorrectly estimating the cloud radiative forcing. Remote-sensing observations of SLW clouds have been carried out for several years at Concordia Station (75° S, 123° E; 3233 m above mean sea level), combining active lidar measurements (SLW cloud detection) and passive HAMSTRAD microwave measurements (liquid water path, LWP). The present project aimed at in situ observations of SLW clouds using sondes developed by the company Anasphere, specifically designed for SLW content (SLWC) measurements. These SLWC sondes were coupled to standard meteorological pressure–temperature–humidity sondes from Vaisala and released under meteorological balloons. During the 2021–2022 summer campaign, 15 launches were made, of which 7 were scientifically exploitable above a height of 400 m above ground level, a threshold height imposed by the time the SLWC sonde takes to stabilize after launch. The three main outcomes from our analyses are as follows: (a) the first in situ observations so far of SLW clouds in Antarctica with SLWC sondes; (b) on average, the consistency of SLW cloud heights as observed by in situ sondes and remote-sensing lidar; and (c) the liquid water path (vertically integrated SLWC) deduced by the sondes being generally equal to or greater than the LWP remotely sensed by HAMSTRAD. In general, the SLW clouds were observed in a layer close to saturation (U > 80 %) or saturated (U ∼ 100 %–105 %) just below or at the lowermost part of the entrainment zone, or capping inversion zone, which exists at the top of the planetary boundary layer and is characterized by an inflection point in the potential temperature vertical profile. Our results are consistent with the theoretical view that SLW clouds form and remain at the top of the planetary boundary layer.
Water vapour plays an important role for the chemistry and dynamics of the atmosphere. It is a strong greenhouse gas in the troposphere and contributes to cooling in the stratosphere. As the main ...source of chemically active
HO
x
radicals, it is linked to many photo-chemical cycles controlling the composition of the middle atmosphere.
In order to improve our knowledge of the amount and variability of water in the middle atmosphere, the Sub-Millimetre Radiometer (SMR) on board the Odin satellite, launched in February 2001, observes several thermal emission lines of water vapour in the 486–581
GHz spectral range from the Earth's limb. Bands centred at 488.9 and 490.4
GHz are used to study water vapour and its isotopes, on the basis of four observation days per month. Vertical profiles of
H
2
O
16
,
H
2
O
18
, and HDO are retrieved between roughly 20 and 70
km in the stratosphere and mesosphere. A strong water vapour line at 556.9
GHz is simultaneously measured in a second band, providing information in the mesosphere and lower thermosphere between about 40 and 100
km. Measurements of
H
2
O
17
at 552.0
GHz in monthly intervals complete the picture of middle atmospheric water vapour provided by Odin/SMR.
The measurements of the isotope HDO in the 20–70
km altitude range allow to study the isotopic ratio of deuterium in stratospheric water vapour
(
D
/
H
)
, potentially supplying information on the origin of stratospheric water vapour: transport of tropospheric air through the tropical tropopause layer (TTL) versus in situ chemical production such as from methane oxidation. The unique measurements of the molecules
H
2
O
18
and
H
2
O
17
containing heavy isotopes of oxygen may provide a crucial test for our understanding of the complex chemical reaction mechanisms controlling the exchange of oxygen between water vapour and ozone.
We use measurements of chlorine monoxide (ClO) by the SMR instrument onboard the Odin satellite to study the nighttime thermal equilibrium between ClO and its dimer Cl2O2. Observations performed in ...the polar vortex during the 2002–2003 Arctic winter showed enhanced amounts of nighttime ClO over a wide range of stratospheric temperatures (185 < T < 225 K). Odin/SMR measurements are here compared to three‐dimensional model calculations using various published estimations of the Keq equilibrium constant between ClO and Cl2O2. Our results show that the value of Keq currently recommended by JPL (Sander et al., 2003) leads to a large underestimation of the observed nighttime ClO amounts, and that a realistic estimation of Keq must lie between the values determined by Cox and Hayman (1988) and Von Hobe et al. (2005).
The Sub‐Millimetre Radiometer (SMR) aboard the Odin satellite has been measuring vertical profiles of atmospheric trace gases since August 2001. We present the inversion methodology developed for CO ...measurements and the first retrieval results. CO can be retrieved from a single scan measurement throughout the middle atmosphere, with a typical resolution of ∼3 km and a relative error of ∼10% to ∼25%. Retrieval results are evaluated through comparison with data from the Whole Atmosphere Community Climate Model (WACCM) and observations of the Improved Stratospheric and Mesospheric Sounder (ISAMS) on board the Upper Atmospheric Research Satellite (UARS). Considering the large natural variability of CO, the SMR retrievals give good confirmation of the WACCM results, with an overall agreement within a factor of 2. ISAMS abundances are higher than SMR mixing ratios by a factor of 5–10 above 0.5 hPa from ∼80°S to ∼50°N.
The airborne submillimeter radiometer (ASUR) was deployed onboard the Falcon research aircraft during the scanning imaging absorption spectrometer for atmospheric cartography (SCIAMACHY) validation ...and utilization experiment (SCIAVALUE) and the European polar stratospheric cloud and lee wave experiment (EuPLEx) campaigns. A large number of ozone profile measurements were performed over a latitude band spanning from 5°S to 80°N in September 2002 and February/March 2003 during the SCIAVALUE and around the northern polar latitudes in January/February 2003 during the EuPLEx. Both missions amassed an ample microwave ozone profile data set that is used to make quantitative comparisons with satellite measurements in order to assess the quality of the satellite retrievals. In this paper, the ASUR ozone profile measurements are compared with measurements from SCIAMACHY and Michelson interferometer for passive atmospheric sounding (MIPAS) on Environmental Satellite and optical spectrograph and infrared imager system (OSIRIS) and submillimeter radiometer (SMR) on the Odin satellite. The cross comparisons with the criterion that the ASUR measurements are performed within ±1000 km and ±6 hrs of the satellite observations show a good agreement with all the four satellite sensors. The differences in data values are the following: −4 to +8% for ASUR‐SCIAMACHY (operational product, v2.1), within ±15% for ASUR‐SCIAMACHY (scientific product, v1.62), up to +6% for ASUR‐MIPAS (operational product v4.61) and ASUR‐MIPAS (scientific product v1‐O3‐1), up to 17% for ASUR‐OSIRIS (v012), and −6 to 17% for ASUR‐SMR (v222) between the 20‐ and 40‐km altitude range depending on latitude. Thus, the intercomparisons provide important quantitative information about the quality of the satellite ozone profiles, which has to be considered when using the data for scientific analyses.
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