Modelling studies of metallic layers in the mesosphere using a GCM model

1. Modelling studies of metallic layers in the mesosphere using a GCM model Wuhu Feng1,2, John Plane1, Martyn Chipperfield2, Dan Marsh3, Diego Jaches4, Chester Gardner5, Alan Liu5, Sandip Dhomse1, Erin Dawkins1,2 , Martin Langowski6 1. Mathematic and physics, School of Chemistry, University of Leeds, U.K. 2. ICAS, School of Earth and Environment, University of Leeds, UK 3. Atmospheric Chemistry Division, NCAR, USA 4. Space Weather Lab, GSFC/NASA, USA 5. University of Illinois at Urbana-Champaign, USA 6. IUP, University of Bremen, Germany 2. WACCM 1. Introduction Changes in the mesosphere are an important signal of climate change. Recent studies show that weather forecasts are significantly improved by extending Numerical Weather Prediction models from the stratosphere to the upper mesosphere. However, the mesosphere is still poorly understood due to limited measurements. Mesospheric metal layers offer a unique way to understand the role of atmospheric chemistry and dynamical processes and test the accuracy of climate models in the upper mesosphere/lower thermosphere (MLT) region (~75-120 km). The major source of metals in the upper atmosphere is the ablation of meteoroids entering the atmosphere (~7-250 tonnes every day) from space. The first aim of this research project is to insert the chemistry of metals like Na, Fe, Ca and Mg into a global chemistry-climate model (WACCM ) and investigate the required meteoric input function (MIF) to simulate realistic mesospheric metal layers. • Whole Atmosphere Community Climate Model uses NCAR CESM software framework. • σ-p coordinates from surface to 140 km (~1.5km in LS and 3 km in MLT). • Detailed dynamics/physics in the Troposphere/Stratosphere/Mesosphere/Thermosphere. • Detailed chemical processes in the atmosphere. • Includes long/short-lived species, and additional surface source gases, radical species. • Ion chemistry and other parameters • Detailed 3D emission inventories of natural and anthropogenic surface sources. • Dry/wet deposition of soluble species. • Lightning and Aircraft production of NOx. • Includes heterogeneous processes, photolysis reactions and gas-phase reactions. • No metal chemistry (Na, Fe, Ca, Mg etc.) in the standard WACCM model. Abstract 2. MIPAS-TOMCAT Comparison Strategy 3. Sodium, Iron and Magnesium Metal Chemistry 4. Metal Meteoric Input Function (MIF) Fig. 2. An example ablation profile from 1D CABMOD model (SZA=35o,entry velocity: 21 km/s, mass=4µg). Fig 1. Sodium, Iron and Magnesium Chemistry in the MLT region (Plane, 2003, 2004). Fig. 3. MIF injection rate of Na, Fe and Mg used for WACCM. 5. Sodium Comparison 6. Iron Comparison Fig 6. Modelled Na and its chemical species at SOR. Fig 5. Mesospheric Na layer comparison from lidar measurement and WACCM at Starfire Optical Range station (SOR) (35oN). Fig 8. Same as Fig. 5, but for Fe at Rothera station (67oS). Fig 4. Na total column density from OSIRS/Odin and WACCM. Fig 7. Modelled Fe total column density. 7. Magnesium Comparison 8. Conclusions Successfully added mesospheric metal (i.e., Na, Fe and Mg) chemistry into the WACCM 3-D chemistry-climate model. The ablation of metals occurs at different altitudes which vary with solar zenith angle, entry velocity and mass (Fig. 2). Seasonal variation of metal injection fluxes (meteoric input function) (Fig. 3). Simulated mesospheric metal density largely depends on how much metal flux put into WACCM. However, there are still big uncertainties in meteoric input function. Our results suggest 7-10 tonnes per day of interplanetary dust needed in WACCM. Overall, WACCM does a good job in simulating the mesospheric metal layers (Figs4-9). However, modelled Na (and Fe) peak layer is 2-3 km lower than observations (Figs5 and 8) because mesopause is lower (~3 km) in WACCM than SABER satellite measurement (not shown), which suggests the gravity wave parameters in WACCM need improvement. The modelled summertime Fe layer is broader than observed (Fig. 8) because the polar mesospheric clouds (PMCs) are weak/missing in WACCM. A detailed PMC scheme is needed in WACCM. WACCM captures the observed peak layers of Mg+ (Fig. 9) and Mg (not shown) but has narrower layer of Mg compared with retrieved data from SCIAMACHY measurements (Fig.10). Further investigation is needed for this discrepancy. Mg+ has higher peak layer (~ 95-100 km) than Mg which is well captured by WACCM (Figs. 9 and 10) . The metal layers have similar seasonal variation (Figs 4, 7 and 11). The size of variation is latitude-dependent. 4. Logos Fig 9. Mesospheric Mg+ layer from WACCM and SCIAMACHY measurement. Fig 11. Same as Fig. 7, but for Mg. Fig 10. Mg layer from WACCM simulation. Institute for Climate and Atmospheric Science, School of Earth and Environment School of Chemistry w.feng@leeds.ac.uk