Abstract
Water vapour and ozone are important for the thermal and radiative balance of the upper troposphere (UT) and lowermost stratosphere (LMS). Both species are modulated by transport processes. Chemical and microphysical processes affect them differently. Thus, representing the different processes and their interactions is a challenging task for dynamical cores, chemical modules and microphysical parameterisations of state-of-the-art atmospheric model components. To test and improve the models, high resolution measurements of the UT/LMS are required. Here, we use measurements taken in a challenging case study by the GLORIA (Gimballed Limb Observer for Radiance Imaging of the Atmosphere) instrument on HALO. The German research aircraft HALO (High Altitude and LOng range research aircraft) performed a research flight on 26 February 2016, which covered deeply subsided air masses of the aged 2015/16 Arctic vortex, high-latitude LMS air masses, a highly textured troposphere-to-stratosphere exchange mixing region, and high-altitude cirrus clouds. Therefore, it provides a multifaceted case study for comparing GLORIA observations with state-of-the-art atmospheric model simulations in a complex UT/LMS region at a late stage of the Arctic winter 2015/16. Using GLORIA observations in this manifold scenario, we test the ability of the numerical weather prediction (NWP)-model ICON (ICOsahedral Nonhydrostatic) with the extension ART (Aerosols and Reactive Trace gases) and the chemistry-climate model (CCM) EMAC (ECHAM5/MESSy Atmospheric Chemistry) to model the UT/LMS composition of water vapour (H2O), ozone (O3), nitric acid (HNO3) and clouds. Within the scales resolved by the respective model, we find good overall agreement of both models with GLORIA. The applied high-resolution ICON-ART setup involving a R2B7 nest (local grid refinement with a horizontal resolution of about 20 km), covering the HALO flight region, reproduces mesoscale dynamical structures well. An observed troposphere-to-stratosphere exchange connected to an occluded Icelandic low is clearly reproduced by the model. Given the lower resolution (T106) of the nudged simulation of the EMAC model, we find that this model also reproduces these features well. Overall, trace gas mixing ratios simulated by both models are in a realistic range, and major cloud systems observed by GLORIA are mostly reproduced. However, we find both models to be affected by a well-known systematic moist-bias in the LMS. Further biases are diagnosed in the ICON-ART O3, EMAC H2O and EMAC HNO3 distributions. Finally, we use sensitivity simulations to investigate (i) short-term cirrus cloud impacts on the H2O distribution (ICON-ART), (ii) the overall impact of polar winter chemistry and microphysical processing on O3 and HNO3 (ICON-ART/EMAC), (iii) the impact of the model resolution on simulated parameters (EMAC), and (iv) consequences of scavenging processes by cloud particles (EMAC). We find that changing of the horizontal model resolution results in notable systematic changes for all species in the LMS, while scavenging processes play only a role in case of HNO3. We need to understand the representativeness of our results. However, this is a unique opportunity to characterise model biases that potentially affect forecasts and projection (adversely), and to discover deficits and define paths for further model improvements.
Highlights
Trace gas composition, in particular the vertical distributions of greenhouse gases, and clouds play an important role in the thermal and radiative budget of the upper troposphere/lowermost stratosphere (UT/LMS) (Riese et al, 2012; Hartmann et al, 2013)
Using GLORIA observations during the HALO long-range flight on 26 February 2016, we test the ability of the ACM ICONART and the CCM ECHAM/MESSy Atmospheric Chemistry (EMAC) to model mesoscale dynamical features, the chemical composition and cirrus clouds and their impacts in the UT/LMS
We have demonstrated that residuals between the active water vapour tracer and the respective tracer neglecting cloud microphysics in the ICON-ART simulation can be used for an 20 alternative proxy for the presence of clouds, in terms of an integrated picture of the short forecast
Summary
In particular the vertical distributions of greenhouse gases, and clouds play an important role in the thermal and radiative budget of the upper troposphere/lowermost stratosphere (UT/LMS) (Riese et al, 2012; Hartmann et al, 2013). Numerical weather prediction and chemistry-climate models (NWPs and CCMs) are capable of resolving the UT/LMS, mesoscale dynamics and cloud processes (in parts) explicitly and by using parameterisations ranging from low to high complexity Examples of such models are the models ICON (ICOsahedral Nonhydrostatic, see Zängl et al, 2015) with the extension ART (Aerosols and Reactive Trace gases, see Rieger et al, 2015 and Schröter et al, 2018) and EMAC 15 (ECHAM5/MESSy Atmospheric Chemistry, see Jöckel et al, 2006, 2010, 2015 and Roeckner et al, 2006). 30 During the research flight on 26 February 2016 (PGS 14), GLORIA probed subsided LMS air masses of the aged 2015/16 polar vortex in high latitudes, a highly textured troposphere-stratosphere exchange region, and high-altitude cirrus clouds across a long transect spanning from Scandinavia over Greenland to Canada.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
