A list of recent published papers involving FAAM
Chapter 4 – Microphysical Properties of Convectively Forced Mixed-Phase Clouds
Robert Jackson, Jeffrey French and Joseph Finlon. Chapter 4 – Microphysical Properties of Convectively Forced Mixed-Phase Clouds. In Constantin Andronache (ed.). Mixed-Phase Clouds. Elsevier, 2018, pages 69 – 96. Abstract The main topic of this chapter is the microphysical properties of convectively forced mixed-phase clouds. Numerous techniques have been used to measure the in situ properties of convectively forced mixed-phase clouds, with various uncertainties in their measurements discussed. It is shown that there is a wide variability in the observed microphysical properties of convective clouds that can be attributed to numerous factors. Finally, some recommendations for future projects sampling convectively forced mixed-phase clouds are discussed. Read more (external link)
The Role of Precipitation in Controlling the Transition from Stratocumulus to Cumulus Clouds in a Northern Hemisphere Cold-Air Outbreak
Steven J Abel, Ian A Boutle, Kirk Waite, Stuart Fox, Philip R A Brown, Richard Cotton, Gary Lloyd, Tom W Choularton and Keith N Bower. The role of precipitation in controlling the transition from stratocumulus to cumulus clouds in a northern hemisphere cold-air outbreak. Journal of the Atmospheric Sciences 74(0):2293–2314, 2017. Abstract Aircraft observations in a cold-air outbreak to the north of the United Kingdom are used to examine the boundary layer and cloud properties in an overcast mixed-phase stratocumulus cloud layer and across the transition to more broken open-cellular convection. The stratocumulus cloud is primarily composed of liquid drops with small concentrations of ice particles and there is a switch to more glaciated conditions in the shallow cumulus clouds downwind. The rapid change in cloud morphology is accompanied by enhanced precipitation with secondary ice processes becoming active and greater thermodynamic gradients in the subcloud layer. The measurements also show a removal of boundary layer accumulation mode aerosols via precipitation processes across the transition that are similar to those observed in the subtropics in pockets of open cells. Simulations using a convection-permitting (1.5-km grid spacing) regional version of the Met Office Unified Model were able to reproduce many of the salient features of the cloud field although the liquid water path in the stratiform region was too low. Sensitivity studies showed that ice was too active at removing supercooled liquid water from the cloud layer and that improvements could be made by limiting the overlap between the liquid water and ice phases. Precipitation appears to be the key mechanism responsible for initiating the transition from closed- to open-cellular convection by decoupling the boundary layer and depleting liquid water from the stratiform cloud. READ MORE (External link)
Ground and Airborne U.K. Measurements of Nitryl Chloride: An Investigation of the Role of Cl Atom Oxidation at Weybourne Atmospheric Observatory.
Thomas J Bannan, Asan Bacak, Michael Le Breton, Michael Flynn, Bin Ouyang, Matthew McLeod, Rod Jones, Tamsin L Malkin, Lisa K Whalley, Dwayne E Heard, Brian Bandy, Anwar M H Khan, Dudley E Shallcross and Carl J Percival. Ground and Airborne U.K. Measurements of Nitryl Chloride: An Investigation of the Role of Cl Atom Oxidation at Weybourne Atmospheric Observatory. Journal of Geophysical Research: Atmospheres 122(20):11,154–11,165, 2017. Abstract Nitryl chloride (ClNO2) measurements from the Weybourne Atmospheric Observatory (WAO) are reported from March to April 2013 using a quadruple chemical ionization mass spectrometer with the I− ionization scheme. WAO is a rural coastal site with generally low NOx concentrations, a type of location poorly studied for ClNO2 production. Concentrations of ClNO2 exceeded that of the limit of detection (0.8 ppt) on each night of the campaign, as did concentrations of N2O5, which was also measured simultaneously with the Cambridge Broadband Cavity Enhanced Absorption Spectrometer. A peak concentration of 65 ppt of ClNO2 is reported here. Vertical profiles of ClNO2 from early- to middle-morning flights in close proximity to WAO are also reported, showing elevated concentrations at low altitude. The photolysis of observed ClNO2 and a box model utilizing the Master Chemical Mechanism modified to include chlorine chemistry was used to calculate Cl atom concentrations. This model utilized numerous VOCs from the second Tropospheric Organic Chemistry project in 2004, at the same location and time of year. From this the relative importance of the oxidation of three groups of measured VOCs (alkanes, alkenes, and alkynes) by OH radicals, Cl atoms, and O3 is compared. Cl atom oxidation was deemed generally insignificant at this time and location for total oxidation due to the much lower concentration of ClNO2 observed, even following the night of greatest ClNO2 production. READ MORE (external link)
Retrievals of the Far Infrared Surface Emissivity Over the Greenland Plateau Using the Tropospheric Airborne Fourier Transform Spectrometer (TAFTS).
Christophe Bellisario, Helen E Brindley, Jonathan E Murray, Alan Last, Juliet Pickering, Chawn R Harlow, Stuart Fox, Cathryn Fox, Stuart M Newman, Maureen Smith, Doug Anderson, Xianglei Huang and Xiuhong Chen. Retrievals of the Far Infrared Surface Emissivity Over the Greenland Plateau Using the Tropospheric Airborne Fourier Transform Spectrometer (TAFTS). Journal of Geophysical Research: Atmospheres 122(22):12,152–12,166, 2017. Abstract The Tropospheric Airborne Fourier Transform Spectrometer measured near surface upwelling and downwelling radiances within the far infrared (FIR) over Greenland during two flights in March 2015. Here we exploit observations from one of these flights to provide in situ estimates of FIR surface emissivity, encompassing the range 80–535 cm−1. The flight campaign and instrumental setup are described as well as the retrieval method, including the quality control performed on the observations. The combination of measurement and atmospheric profile uncertainties means that the retrieved surface emissivity has the smallest estimated error over the range 360–535 cm−1 (18.7–27.8 μm), lying between 0.89 and 1 with an associated error that is of the order ±0.06. Between 80 and 360 cm−1, the increasing opacity of the atmosphere, coupled with the uncertainty in the atmospheric state, means that the associated errors are larger and the emissivity values cannot be said to be distinct from 1. These FIR surface emissivity values are, to the best of our knowledge, the first ever from aircraft-based measurements. We have compared them to a recently developed theoretical database designed to predict the infrared surface emissivity of frozen surfaces. When considering the FIR alone, we are able to match the retrievals within uncertainties. However, when we include contemporaneous retrievals from the mid-infrared (MIR), no single theoretical representation is able to capture the FIR and MIR behaviors simultaneously. Our results point toward the need for model improvement and further testing, ideally including in situ characterization of the underlying surface conditions. READ MORE (External link)