Multi-scale Modelling of Mesospheric Metals (4M)

Lead Research Organisation: University of Leeds
Department Name: Sch of Chemistry

Abstract

Roughly 50 tonnes of interplanetary dust enters the earth's atmosphere every day. The dust particles collide with air molecules at speeds between 11 and 72 km/s, causing most of the particles to flash heat, melt and evaporate. This produces metal atoms which then appear in layers between about 75 and 110 km. The Na, Fe, Ca and Ca+ layers have been observed since the 1970s using the ground-based lidar technique. Recently it has become possible to observe the metal layers, including Mg and Mg+, on a global basis using optical instruments on satellites. The need to explain these atmospheric observations has stimulated laboratory studies of the reactions which these metals and their ions undergo in the atmosphere, and the consequent development of local scale atmospheric models. The mesospheric metal layers are extremely useful probes of the chemistry and dynamics of the upper atmosphere. This is because the layers, whose widths of just a few km are controlled by fast photochemical processes, are very responsive to dynamical processes such as gravity waves and tides, and changes in atmospheric constituents such as O, H and O3. Noctilucent clouds, which form around 83 km when the temperature falls below 150 K during summer at high latitudes, cause substantial depletion of the metal layers because of rapid uptake of the metals on the ice surfaces. During winter at high latitudes, convergence of the meridional circulation over the polar vortex appears to cause a substantial increase in the metal concentrations. Solar proton events also cause significant perturbations to the metal layers. Lastly, the chemistry which controls the heights of the layers is largely driven by atmospheric pressure, and so the layer heights are sensitive to global cooling caused by increasing greenhouse gases such as CO2 and CH4 in the middle atmosphere. The objective of this proposal is to produce the first global model of four metals - sodium, iron, calcium and magnesium. These metals all behave quite differently in the mesosphere. We will insert the chemistry of these metals into a state-of-the-art general circulation model, the Whole Atmosphere Chemistry Climate Model (WACCM), which has been developed at the US National Center for Atmospheric Research over the past decade. This general circulation model extends from the earth's surface to 140 km, and includes all the neutral and ionized constituents with which the metals interact. In preparation for this project, we have recently installed and run WACCM on the UK's front-line national supercomputing service HECToR (High-End Computing Terascale Resource). Modelling the metal layers also requires as input the rates at which each metal is injected into the atmosphere from ablating interplanetary dust, as a function of height, season, latitude and time-of-day. These injection rates will be calculated using our new Chemical Ablation Model, combined with an astronomical model of the meteor input function. A project student will retrieve, for the first time, a global data set of Fe and Fe+ observations, using the SCIAMACHY instrument on ENVISAT. This will supplement the ground-based lidar measurements of Fe. The WACCM predictions of the metal layer densities, peak heights, and diurnal and seasonal variability will be compared with the observational data base. The WACCM mesospheric winds and temperatures will also be compared with measurements. These comparisons will enable the WACCM mesosphere to be optimised e.g. through higher vertical resolution and better treatment of gravity waves. We will then investigate the likely impact of the solar cycle and climate change on the distributions of all four metals, for instance as a guide to future observations. Finally, the improved model will be used to study the impact of the mesosphere on stratospheric ozone and climate.

Publications

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Dawkins EC (2015) The near-global mesospheric potassium layer: Observations and modeling. in Journal of geophysical research. Atmospheres : JGR

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Dunker T (2015) Mesospheric temperatures and sodium properties measured with the ALOMAR Na lidar compared with WACCM in Journal of Atmospheric and Solar-Terrestrial Physics

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Feng W (2017) Impacts of a sudden stratospheric warming on the mesospheric metal layers in Journal of Atmospheric and Solar-Terrestrial Physics

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Feng W (2015) Diurnal variation of the potassium layer in the upper atmosphere. in Geophysical research letters

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Feng W (2013) A global atmospheric model of meteoric iron A GLOBAL METEORIC IRON MODEL in Journal of Geophysical Research: Atmospheres

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Marsh D (2013) A global model of meteoric sodium GLOBAL MODEL OF METEORIC SODIUM in Journal of Geophysical Research: Atmospheres

 
Description Metals are injected into the atmosphere when cosmic dust enters at high speeds and ablates between 80 and 120 km altitude. The purpose of this grant was to develop a global model of the six most important metals - Na, K, Fe, Mg, Ca and Si. This required a description of the injection of each of these metals as a function of height and location, and over 120 chemical reactions in addition to the standard atmospheric chemistry scheme in a global chemistry-climate model. Detailed comparisons of the model with lidar and satellite measurements of three metals - Na, Fe and Mg - have been carried out. The model in general performs very successfully.

A second part of the project was to develop a satellite retrieval scheme in order to gain a near-global picture of the metal layers. This was done using the ODIN/OSIRIS and the ENVISAT/SCIAMACHY satellites/spectrometers, for K/Na and Mg/Mg+, respectively. The K layer has a distinctive semi-annual variation - unlike all the other metals that have been observed. A new model of K chemistry was developed using electronic structure theory to predict the rates of key reactions. This model successfully accounts for the seasonal behaviour of this metal, solving a problem that has been around for more than 40 years.

The final part of the project was to carry out long model runs to determine which of these metals is sensitive to the solar cycle and climate change. It turns out that the K layer is very sensitive to both of these, and over 50 years the model predicts there will have been a nearly 20% increase in the K column abundance since 1955.
Exploitation Route The Whole Atmosphere Community Climate Model with metal chemistry will be available to the community once it has been validated by NCAR.

The satellite retrieval algorithm will be useful for future satellite missions using UV-VIS spectrometers
Sectors Aerospace, Defence and Marine,Environment

URL http://www1.chem.leeds.ac.uk/JMCP/
 
Description The metal chemistry which has been put into the Whole Atmosphere Community Climate Model will be made available through NCAR in the US.
First Year Of Impact 2014
Sector Aerospace, Defence and Marine,Environment
Impact Types Cultural

 
Description EOARD
Amount $25,000 (USD)
Funding ID FA8655-09-1-3015 
Organisation United States Air Force 
Sector Public
Country United States
Start 01/2009 
End 12/2010
 
Description EOARD
Amount $50,000 (USD)
Funding ID FA8655-10-1-3045 
Organisation United States Air Force 
Sector Public
Country United States
Start 04/2010 
End 11/2011
 
Description ERC Advanced Grant
Amount € 2,480,000 (EUR)
Funding ID 291332 CODITA 
Organisation European Research Council (ERC) 
Sector Public
Country European Union (EU)
Start 04/2012 
End 03/2017
 
Description Collaboration with Dr Daniel Marsh 
Organisation NCAR National Center for Atmospheric Research
Country United States 
Sector Academic/University 
PI Contribution Developed chemical models of the meteoric metal layers
Collaborator Contribution Provided the Whole Atmosphere Community Climate Model
Impact Several published papers
Start Year 2009
 
Description Collaboration with Dr Diego Janches 
Organisation National Aeronautics and Space Administration (NASA)
Department Goddard Space Flight Center
Country United States 
Sector Public 
PI Contribution Provided output from the CABMOD ablation model to interpret radar observations. Created metal layer chemistry models.
Collaborator Contribution Provided radar measurements of meteor head echoes. Provided a meteoric input function for the global model of metal chemistry
Impact Two jointly authored papers.
Start Year 2007