A study of clear sky closure study using high resolution far-IR spectra from the high arctic

Lead Research Organisation: Imperial College London
Department Name: Dept of Physics

Abstract

The Earth's energy balance is in equilibrium, that is to say, an equal amount of energy is absorbed and emitted, The Sun is the source of all energy for the Earth, heating the planet via sunlight, warming the surface and this energy is emitted back into space as heat. A simple calculation can be made to estimate the surface temperature needed to preserve this equilibrium, and is about 255K, or -18degC. The presence of gases in the atmosphere that can absorb heat (greenhouse gases, such as water vapour and carbon dioxide), affects this basic equilibrium, meaning that it isn't generally the surface, but a layer of the atmosphere some distance above our heads that releases the energy to space; keeping the surface warmer than we would initially expect, and habitable for us humans. Once we look into what actually happens in more detail, this picture becomes very complicated. For instance, whether the surface is covered by ocean, desert, forests or snow makes a big difference, as does the concentration of greenhouse gases through the depth of the atmosphere and the amount, height and type of any cloud. Generally speaking, in the tropics more energy is absorbed than is emitted back to space; the winds and oceans transport this excess heat north and south towards the poles. At the other extreme, the Arctic region absorbs very little sunlight, and emits more energy to space than it receives. There is highly reflective snow and ice in the Arctic region and because it is so cold, the air is relatively dry compared to lower latitudes. With water vapour being one of the major greenhouse gases, the Arctic doesn't trap the heat as well as in the tropics. In some places and meteorological situations, parts of the heat (infra-red) spectrum of the atmosphere become transparent, allowing the surface to cool directly to space, removing some of the warming effect of the atmosphere. Where this happens is very interesting for scientists who try to understand the subtle mechanisms that control the loss of heat from the atmosphere. Using the Imperial College high resolution far infrared spectrometer (TAFTS), together with the US spectrometer (AERI-ER) we have taken measurements of the whole infrared spectrum from a site in the high arctic, where these rare conditions occur. The site was the United States Department of Energy (DoE) Atmospheric Radiation Measurement (ARM) site in Barrow, Alaska, in the spring of 2007. These measurements allow us to look up through these transparent windows to study the interaction between the greenhouse gases and thermal radiation in these dry conditions. These measurements were funded by the US ARM program, with initial analysis having shown that the data is of good quality and of scientific use. We now wish to analyse this data to take the full scientific benefit and impact from it. In addition to the infrared measurements of spectral radiances, we have the auxiliary data, which defines the state of the atmosphere, both the temperature and water vapour profile throughout the atmosphere, evidence for the lack of clouds etc. Using these datasets we are aiming to be able to better quantify the strength of the water vapour absorption lines, and the underlying absorption by water vapour, known as the continuum absorption. We will also use our results and models to investigate the cooling to space in the far infrared. This work will improve our understanding of the atmosphere, with many applications in radiation components of global climate models, and is expected to give greater accuracy in atmospheric models.
 
Description The Earth's energy balance is in equilibrium, that is to say, an equal amount of energy is absorbed and emitted, The Sun
is the source of all energy for the Earth, heating the planet via sunlight, warming the surface and this energy is emitted
back into space as heat. A simple calculation can be made to estimate the surface temperature needed to preserve this
equilibrium, and is about 255K, or -18degC. The presence of gases in the atmosphere that can absorb heat (greenhouse
gases, such as water vapour and carbon dioxide), affects this basic equilibrium, meaning that it isn't generally the surface,
but a layer of the atmosphere some distance above our heads that releases the energy to space; keeping the surface
warmer than we would initially expect, and habitable for us humans. Once we look into what actually happens in more
detail, this picture becomes very complicated. For instance, whether the surface is covered by ocean, desert, forests or
snow makes a big difference, as does the concentration of greenhouse gases through the depth of the atmosphere and
the amount, height and type of any cloud.
Generally speaking, in the tropics more energy is absorbed than is emitted back to space; the winds and oceans transport
this excess heat north and south towards the poles. At the other extreme, the Arctic region absorbs very little sunlight,
and emits more energy to space than it receives. There is highly reflective snow and ice in the Arctic region and because
it is so cold, the air is relatively dry compared to lower latitudes. With water vapour being one of the major greenhouse
gases, the Arctic doesn't trap the heat as well as in the tropics. In some places and meteorological situations, parts of the
heat (infra-red) spectrum of the atmosphere become transparent, allowing the surface to cool directly to space, removing some of the warming effect of the atmosphere. Where this happens is very interesting for scientists who try to understand the subtle mechanisms that control the loss of heat from the atmosphere.
Using the Imperial College high resolution far infrared spectrometer (TAFTS), together with the US spectrometer (AERI-ER) we have taken measurements of the whole infrared spectrum from a site in the high arctic, where these rare
conditions occur. The site was the United States Department of Energy (DoE) Atmospheric Radiation Measurement (ARM) site in Barrow, Alaska, in the spring of 2007. These measurements allow us to look up through these transparent windows to study the interaction between the greenhouse gases and thermal radiation in these dry conditions. These measurements were funded by the US ARM program. In this grant award we analysed this data to take the full scientific benefit and impact from it. In addition to the infrared measurements of spectral radiances, we have the auxiliary data, which defines the state of the atmosphere, both the temperature and water vapour profile throughout the atmosphere, evidence for the lack of clouds etc. Using these datasets we have been able to better quantify the strength of the water vapour absorption lines,
and the underlying absorption by water vapour, known as the water vapour continuum absorption. We also used our results and models to investigate the cooling to space in the far infrared. This work has improved our understanding of the
atmosphere, with many applications in radiation components of global climate models, and is giving greater
accuracy in atmospheric models.
Exploitation Route Our measurements of the water vapour continuum are used in modelling of radiative transfer in the Earth's atmosphere, and are thus providing greater accuracy and reliability in atmospheric models.
Sectors Environment

 
Description Our findings have been used in modelling of radiative transfer in the Earth's atmosphere, to improve the reliability of the modelling of absorption of radiation by water vapour, a key greenhouse gas. Thus there is impact in atmospheric modelling and climate modelling.
First Year Of Impact 2015
Sector Environment
Impact Types Societal

 
Description Physics talk at Engineering Headstart course 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Geographic Reach National
Primary Audience Schools
Results and Impact talk generated questions and discussions

I have seen applications to Physics from some of the school pupils attending the Engineering Headstart courses
Year(s) Of Engagement Activity 2014,2015,2016
 
Description Physics talk at University Open Day 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Geographic Reach National
Primary Audience Schools
Results and Impact Talk generated many questions and discussions.

We receive applications from school pupils who have attended our Open Days
Year(s) Of Engagement Activity 2014,2015,2016
 
Description School Visit, Ealing, 2013 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact 48 year 5 pupils in girls primary school attended my workshop/talk on the size of the Universe, with many many questions being asked by the pupils!

I was asked by the teachers if I would be willing to return to give more talks as the girls were very enthusiastic.
Year(s) Of Engagement Activity 2013
 
Description School Workshop 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact I ran a workshop about studying science at University, and how to apply through UCAS. The pupils were asked to consider their skills,interests, hobbies, work experience, and plan ahead in terms of what they could do, at school or out of school, with their goal in mind to give them the best chance of studying the degree of their choice. They worked in small teams on tasks I set, and we had discussions resulting from this.

The school (a local comprehensive) had wanted the workshop to encourage their year 11 and 12s to consider studying sciences at University, and gave me feedback that the workshop was just what they had wanted to inspire their pupils and dispel some myths.
Year(s) Of Engagement Activity 2013
 
Description Women in Physics Open Day, Imperial College London 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Schools
Results and Impact Approximately 300 pupils from schools across the country came of our Women In Physics events held at Imperial College London. The PI of the grant was involved in talks to these girls, encouraging them to think about applying to study physics. The research of the grant award was describe in these talks as an example on ongoing research. Impact may be seen in increased applications from women to us to study physics.
Year(s) Of Engagement Activity 2015,2016
 
Description Women in physics talk 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Schools
Results and Impact Presentations and special event to encourage more women to study physics at university
Year(s) Of Engagement Activity 2014,2015,2016,2017