East Asian summer monsoon delivers large abundances of very-short-lived organic chlorine substances to the lower stratosphere.

Deep convection in the Asian summer monsoon is a significant transport process for lifting pollutants from the planetary boundary layer to the tropopause level. This process enables efficient injection into the stratosphere of reactive species such as chlorinated very-short-lived substances (Cl-VSLSs) that deplete ozone. Past studies of convective transport associated with the Asian summer monsoon have focused mostly on the south Asian summer monsoon. Airborne observations reported in this work identify the East Asian summer monsoon convection as an effective transport pathway that carried record-breaking levels of ozone-depleting Cl-VSLSs (mean organic chlorine from these VSLSs ~500 ppt) to the base of the stratosphere. These unique observations show total organic chlorine from VSLSs in the lower stratosphere over the Asian monsoon tropopause to be more than twice that previously reported over the tropical tropopause. Considering the recently observed increase in Cl-VSLS emissions and the ongoing strengthening of the East Asian summer monsoon under global warming, our results highlight that a reevaluation of the contribution of Cl-VSLS injection via the Asian monsoon to the total stratospheric chlorine budget is warranted.

Validation of H2O continuum absorption models in the wave number range 180-600 cm(-1) with atmospheric emitted spectral radiance measured at the Antarctica Dome-C site.

This work presents the results concerning the analysis of a set of atmospheric emitted (down welling) spectral radiance observations in the spectral range 180 to 1100 cm(-1) acquired at the Dome-C site in Antarctica during an extensive field campaign in 2011-2012. The work has been mainly focused on retrieving and validating the coefficients of the foreign contribution to the water vapour continuum absorption, within a spectral range overlapping the water vapour rotational band. Retrievals have been performed by using a simultaneous physical retrieval procedure for atmospheric and spectroscopic parameters. Both day (summer) and night (winter) spectra have been used in our analysis. This new set of observations in the far infrared range has allowed us to extend validation and verification of state-of-art water vapour continuum absorption models down to 180 cm(-1). Results show that discrepancies between measurements and models are less than 10% in the interval 350-590 cm(-1), while they are slightly larger at wave numbers below 350 cm(-1). On overall, our study shows a good consistency between observations and state-of-art models and provides evidence toward needing to adjust absorptive line strengths. Finally, it has been found that there is a good agreement between the coefficients retrieved using either summer or winter spectra, which are acquired in far different meteorological conditions.

Retrieval of foreign-broadened water vapor continuum coefficients from emitted spectral radiance in the H2O rotational band from 240 to 590 cm(-1).

The paper presents a novel methodology to retrieve the foreign-broadened water vapor continuum absorption coefficients in the spectral range 240 to 590 cm(-1) and is the first estimation of the continuum coefficient at wave numbers smaller than 400 cm(-1) under atmospheric conditions. The derivation has been accomplished by processing a suitable set of atmospheric emitted spectral radiance observations obtained during the March 2007 Alps campaign of the ECOWAR project (Earth Cooling by WAter vapor Radiation). It is shown that, in the range 450 to 600 cm(-1), our findings are in good agreement with the widely used Mlawer, Tobin-Clough, Kneizys-Davies (MT CKD) continuum. Below 450 cm(-1) however the MT CKD model overestimates the magnitude of the continuum coefficient.

Breadboard of a Fourier-transform spectrometer for the radiation explorer in the far infrared atmospheric mission.

In preparation for a possible space mission, a breadboard version named REFIR-BB of the Radiation Explorer in the Far Infrared (REFIR) instrument has been built. The REFIR is a Fourier-transform spectrometer with a new optical layout operating in the spectral range 100-1100 cm(-1) with a resolution of 0.5 cm(-1), a 7-s acquisition time, and a signal-to-noise ratio of better than 100. Its mission is the spectral measurement in the far infrared of the Earth's outgoing emission, with particular attention to the long-wavelength spectral region, which is not covered by either current or planned space missions. This measurement is of great importance for deriving an accurate estimate of the radiation budget in both clear and cloudy conditions. The REFIR-BB permits the trade-off among all instrument parameters to be studied, the optical layout to be tested, and the data-acquisition strategy to be optimized. The breadboard could be used for high-altitude ground-based campaigns or could be flown for test flights on aircraft or balloon stratospheric platforms. The breadboard's design and the experimental results are described, with particular attention to the acquisition strategy and characterization of the interferometer. Tests were performed both in laboratory conditions and in vacuum. Notwithstanding a loss of efficiency above 700 cm(-1) caused by the poor performance of the photolithographic polarizers used as beam splitters, the results demonstrate the feasibility of using the spectrometer for space applications.

SAFIRE-A (spectroscopy of the atmosphere by far-infrared emission-airborne): optimized instrument configuration and new assessment of improved performance.

An upgraded configuration of the SAFIRE-A Fourier transform far-infrared spectrometer was recently set up, and significant improvements in instrument performance were attained during several testing and scientific flights onboard the high-altitude research aircraft M55-Geophysica. New features were implemented in specific instrument subsystems, such as the pointing system, the reference laser interferometer, and the onboard calibration unit, to increase the overall instrument functionality and to obtain reliable operation from both the high-frequency (approximately 120 cm(-1)) and the low-frequency (approximately 23 cm(-1)) detection channels. Other changes, such as those made in the onboard recording system or in the postflight data-transfer procedure, were aimed at expanding the capability of unattended operation and at providing a user-friendly interface for data downloading and ground servicing. A detailed description of these modifications is given, along with a quantitative assessment of the SAFIRE-A instrument performance.