One of the enduring uncertainties about climate change is the importance of aerosols. Their chemistry and effect on the climate is complex. Some of them reflect sunlight immediately back into space, having a net cooling effect on the planet; others (like black carbon have a warming effect. Some aerosols interact with one another, and with other chemicals in the atmosphere, in ways that affect the climate. All of this ought to be better understood, if we want to understand how human activities (and natural phenomena) are affecting the climate, and so that we can prioritize on what sorts of emissions to reduce.
I was surprised to learn, from James Hansen’s recent book, Storms of My Grandchildren, that we have known since the 1970s what sort of instruments would be necessary to understand how aerosols affect the climate system, including whether their net effect is a warming or a cooling one. We need:
- A polarimeter, measuring the polarization of sunlight reflected off of aerosols
- An interferometer, measuring the infrared radiation being emitted by the Earth
- An instrument to measure the sun’s irradiance
- An instrument to measure aerosols and gases in the highest layers of Earth’s atmosphere, by observing the sun shining through them at sunlight and sunset.
The first two would have to be on the same small satellite. The other two would be on small satellites of their own. Together, these would allow us to determine the total forcing effect of aerosols on the climate.
The fact that we apparently aren’t rushing to get these devices built and launched has to be considered a massive failure of intelligence, far beyond the WMD-tomfoolery that preceded the Iraq war. These four instruments could be producing key data to let us understand our climate, at a time when we are running a dangerous global experiment on how it responds to our pollution.
Getting this data must become an international priority.
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Some further information:
“Precise monitoring of solar irradience, the amount of solar radiation reaching Earth, began in the late 1970s.” (Hansen p.103)
In 2004:
“I could report that work had started on the polarimeter, but I was skeptical about whether it would ever be completed…” (Hansen p.109)
“The importance of knowing the actual aerosol forcing is thus obvious. The missing aerosol measurement was the principle objective of the Climsat mission, which I proposed at the Gore-Mikulski roundtable meetings in 1989 and 1990… The satellite mission never took place.”
(Hansen p.100)
The Glory spacecraft uses Orbital Science Corporation’s LEOStar bus design, with deployable solar panels, 3-axis stabilization, and X-band/S-band RF communications capabilities. The structure consists of an octagonal aluminum space frame and a hydrazine propulsion module containing enough fuel for at least 36 months of service. The spacecraft bus also provides payload power; command, telemetry, and science data interfaces, including onboard storage of data; and an attitude control subsystem to support instrument requirements.
Aerosol Polarimetry Sensor
The Aerosol Polarimetry Sensor (APS) is a continuous scanning sensor that has the capability to collect visible, near infrared, and short-wave infrared data scattered from aerosols and clouds. It is designed to make extremely accurate multi-angle observations of Earth and atmospheric scene spectral polarization and radiance.
Total Irradiance Monitor
The Total Irradiance Monitor (TIM) is an electrical substitution radiometer (ESR) that records total solar irradiance with extreme accuracy and precision. It has four identical radiometers to provide redundancy and to help detect changes in the instrument from exposure to solar radiation. TIM is mounted on a platform that points the instrument toward the Sun independently of the spacecraft.
Cloud Camera Sensor Package
The Cloud Camera Sensor Package is a dual-band (blue and near infrared), visible imager utilizing a non-scanning detector arrays that are analogous to star trackers but Earth-viewing. It consists of an optical imaging system that provides continuous cross-track coverage over a field of view centered on the APS along-track footprint.
What is the A-Train?
The “A-Train” satellite constellation will consist of seven satellites flying in close proximity. Each individual mission has its own science objectives; all will improve our understanding of aspects of the Earth’s climate. The synergism that is expected to be gained by flying in close proximity to each other should enable the overall science results of the Afternoon Constellation to be greater than the sum of the science of each individual mission.
The A-Train formation will help answer these important questions.
* What are the aerosol types and how do observations match global emission and transport models?
* How do aerosols contribute to the Earth Radiation Budget (ERB)/climate forcing?
* How does cloud layering affect the Earth Radiation Budget?
* What is the vertical distribution of cloud water/ice in cloud systems?
* What is the role of Polar Stratospheric Clouds in ozone loss and denitrification of the Arctic vortex?
History of the A-Train
NASA launched the Aqua satellite on May 4, 2002 and it is currently performing nominally on orbit. On July 15, 2004, the Aura satellite was launched and phased with Aqua such that one of the Aura instruments, the Microwave Limb Sounder (MLS), is able to view the same air mass that Aqua observed eight minutes earlier. In 2008, Aura was moved forward to eliminate this eight minute delay. The joint NASA/CNES CALIPSO, and the CloudSat missions were launched on April 28, 2006. Both launched on the same expendable launch vehicle and CALIPSO flies from 30 to 120 seconds behind Aqua with CloudSat currently leading CALIPSO by 17.5±2.5 seconds. This tight formation enables synergistic measurements with Aqua, which is a key science requirement for the Afternoon Constellation. A French mission, PARASOL, was launched on December 18, 2004 by the French Space Agency/CNES and flies 58 seconds behind the CALIPSO control box.
I wish there was someone I could ask about whether this collection of satellites will collect the data that Hansen highlighted as being so necessary.
Enter the Solar Dynamics Observatory—”SDO” for short—slated to launch on Feb. 9, 2010, from the Kennedy Space Center in Florida.
SDO is designed to probe solar variability unlike any other mission in NASA history. It will observe the sun faster, deeper, and in greater detail than previous observatories, breaking barriers of time-scale and clarity that have long blocked progress in solar physics.
Change of climate forcings, in watts per square meter, between 1750 and 2000. Vertical bars show estimated uncertainty. Uncertainty for “other greenhouse gases” is similar to that for carbon dioxide. (Data from Hansen et al., “Efficacy of Climate Forcings.” See sources.)
Notes from conversation – 25 June 2010
1) Instruments for measuring aerosols
-not simple to measure
-distribution of sizes, shapes, and types
-located variably in terms of both altitude and geographic location
-some measurement techniques are better than others
-for instance, there are many research instruments which are accurate but have a narrow field of view
-illustrated by recent volcano in Iceland
-considerable uncertainty about location and direction of aerosols, including the most dangerous ones for aircraft
-largely due to how narrow data from LIDAR instruments is
-temporal frequency of measurement also an issue
-some instruments – like MISER on TERRA – have swathes of several hundred kilometres
-polarimeters are necessary for identifying aerosol types
-quantifying the total climate impact of aerosols requires not just an interferometer, but a spectrometer specifically
-this is to measure outgoing radiation (especially infrared)
-it should be on the same satelite as the irradiance instrument looking at the sun
-Earth’s radiation budget comprises a wide range of frequencies
-for instance, lots of UV in incoming sunlight
-high albedo parts of the Earth reflect many of the wavelengths in sunlight
-other areas absorb much more (water, vegetation)
-many instruments are measuring these things
-aerosol concentrations change on short timescales, such as when they are rained out of the atmosphere
-space based instruments don’t always provide the necessary spacial and temporal precision to see how they work
-there are aerosols in the troposphere (lower atmosphere) and stratosphere (15-50km up)
-solar occultation is measured by a Canadian satelite called SCISAT
-30 measurements per day
-self-calibrating and very accurate
-used to calibrate data from other instruments with a wider field of view, such as NASAs AURA
-AURA cost $600-800M, SCISAT just C$65M
-provides a ‘gold standard reference’
-now a geriatric instrument, could fail at any time
-seeking to put a replacement instrument on the ISS – cheapest possible option
-climate monitoring requires the tracking of long-term trends
-also, measurements with very small errors, low signal-to-noise
-allows comparison between years and decades
-importance of black carbon to climate change uncertain
-data not as good as would be ideal
-uncertainty about overall effects of aerosols largely because of uncertainties about aerosol-cloud interactions
-this is one of the biggest uncertainties within climate models
-improved data could help improve models
-useful documents available from The Global Climate Observing System (GCOS)
A fistful of dust
The true effect of windblown material is only now coming to be appreciated
ON MAY 26th 2008 Germany turned red. The winds of change, though, were meteorological, not political. Unusual weather brought iron-rich dust from Africa to Europe, not only altering the colour of roofs and cars on the continent but also, according to recent calculations by Max Bangert, a graduate student at the Karlsruhe Institute of Technology, making the place about a quarter of a degree colder for as long as the dust stayed in the air.
Unusual for Germany; commonplace for the planet as a whole. The Sahara and other bone-dry places continually send dust up into the atmosphere, where it may travel thousands of kilometres and influence regional weather, the global climate and even the growth of forests halfway around the planet.
Earlier in 2008, for instance, Ilan Koren and his colleagues at the Weizmann Institute of Science, in Israel, detected a particularly voluminous burst of dust from the Bodélé Depression. This low-lying bed of silt in Chad, across which powerful jets of wind are wont to blow, constitutes less than 1% of the Sahara’s area but is reckoned the world’s dustiest place. It is thought to be responsible for a quarter or more of the Sahara’s output of airborne dust.
Dr Koren observed the dust rise with a camera on a satellite called Aqua; watched it obscure the sun using an automated photometer in Ilorin, Nigeria; followed it across the Atlantic with another satellite, CALIPSO; and finally saw a spike in levels of silicon, aluminium and iron as it landed on detectors in Manaus, Brazil. His results, presented at a meeting of the American Geophysical Union held in San Francisco in December, provide a remarkable account of the intercontinental transfer of dust.
Which of satellite- or model-based estimates is closer to reality for aerosol indirect forcing?
Johannes Quaas, Olivier Boucher, Nicolas Bellouin, and Stefan Kinne
Reply to Quaas et al.: Can satellites be used to estimate indirect climate forcing by aerosols?
Joyce E. Penner, Cheng Zhou, Li Xu, and Minghuai Wang