Sunday, September 30, 2007

Causes of the reduction in uncertainty in the anthropogenic radiative forcing of climate betweeen IPCC (2001) and IPCC (2007)

The Inter-governmental Panel on Climate Change reviews the best available scientific information on climate change and publishes a report every 5-6 years. The fourth assesment report was released this year and is the IPCC 2007 report. In contrast to the IPCC 2001 report, this report emphasizes with greater confidence that global warming is due to human/anthropogenic activities. Until recently, the sign of the anthropogenic radiative forcing was uncertain largely due to the uncertainty associated with radiative effects (direct and indirect) of atmospheric aerosols. Haywood and Schulz in their recent paper (titled above) inter-compare the probability distribution function of anthropogenic radiative forcing from IPCC 2001 and IPCC 2007 and show that a significant progress has been made in reducing the uncertainty in anthropogenic radiative forcing since IPCC 2001. They conclude that " the single most contributor to this conclusion appears to be the reduction in the uncertainty associated with the aerosol direct effect, followed by the provision of a best estimate for the aerosol cloud albedo indirect effect ".

References :

Haywood, J. M., and M. Schulz (2007), Causes of the reduction in uncertainty in the anthropogenic radiative forcing of climate between IPCC (2001) and IPCC (2007), Geophys. Res. Lett., doi:10.1029/2007GL030749, in press.

Sunday, September 23, 2007

UN/Austria/ESA Symposium on “Space Tools and Solutions for Monitoring the Atmosphere in Support of Sustainable Development”: My Experience

The United Nations (UN) office for outer space affairs, the government of Austria and the European Space Agency (ESA) jointly organized a symposia on “space tools and solution for monitoring the atmosphere in support of sustainable development”. The United Nations invites participants from several nations to attend the symposium every year. There were more than 70 scientists representing more than 41 countries who gathered in Graz, Austria during September 11-14 to discuss various available space tools for monitoring the atmosphere in support of sustainable development. This year’s symposium included a hands-on tutorial and interactive training session on “Satellite Tools and Applications for Air Quality”. I was part of the team, which developed material and conducted the training session. I would really like to take this opportunity to thank my supervisor Dr. Sundar Christopher for providing me this wonderful opportunity and NASA’s applied science program manager Lawrence Friedl for financial support and organizers of the symposium for giving me this amazing opportunity to attend the symposium. It was indeed a great experience to meet and listen to many scientists from different parts of the world on many different aspects of air quality and monitoring atmospheric composition using satellite measurements.

The symposium was a good combination of invited talks, participant presentations and hands-on training workshop. Invited talks covered several important areas including overview of earth observations, satellite applications for atmospheric monitoring, global and regional initiatives, air quality (ozone and particulate matter), climate change and weather.

Hands-on training on satellite tools for air quality monitoring was informative and every single participant experienced handing of satellite data and I am very sure they enjoyed it immensely. The training used four different case studies of heavy aerosol events when particulate matter air quality on the surface was very poor in the region. Case studies covered two recent biomass burning events, one dust storm and one with a mixture of urban pollution and smoke from fires. The participants from the symposium were divided into groups of 3-4 people and each group was provided with a laptop computer. After initial introduction on monitoring air pollution from satellite observations, each group analyzed one case study. Air quality analysis includes identifying different features such as aerosols, clouds, water, land etc in the satellite images, quantifying aerosol loading using aerosol optical thickness, observations on local meteorological conditions and back trajectory analysis to track air mass in and out from the regions of interest. One of the most important parts of this exercise was to obtain different data sets and images from freely available online resources. Every group liked this part and learnt simple solutions to address specific air quality events using satellite imagery. Finally, participants used the tools that they learnt in the workshop to identify air quality color codes in their city or region of interest.

I really enjoyed the entire training session and discussed many different issued related to air quality in different parts of the world. The last day of the symposium was used to identify different problem associated with air quality research and monitoring of air pollution in the participant's country or region. There were several recommendations made by two working groups on air quality monitoring network, data sharing, and policy related issues to the United Nations.

Evening receptions and tours within Graz city were wonderful and served as a time of relaxation after the busy working days for all participants.

Finally, I would like to congratulate and thank all the people who were directly or indirectly involved in organizing such a great successful symposium.

More details about the symposium can be found out on following web link

(Pawan Gupta)
The University of Alabama in Huntsville
Huntsville, AL, USA

P.S: The participants were eager to know the various resources that are available to them on the internet for various data sources. Here are a list if some websites that will be useful.

GIOVANNI: MODIS, MISR, TOMS, OMI aerosol daily and monthly data can be obtained and visualize online using various options available.

MODIS Atmosphere: Details description on MODIS atmospheric products such as aerosols, clouds, water vapor and atmospheric profiles. This is very good site to learn about data, algorithms and updates on publications.

MODIS Rapid Response System: True-color, photo-like imagery and false-color imagery are available within a few hours of being collected by MODIS.

NASA Visible Earth: This is good catalog for different Earth’s images from NASA.

International Air Quality: This site is hosted on USEPA webpage, which provides link to available online resources for international air quality monitoring.

IDEA: This site provides surface and satellite assessment of particulate matter air quality over United States.

NRL Aerosol Page: This site provides model forecasts of various aerosol fields for global regions. This site also maintain very good list of links related to atmospheric aerosol research.

Monday, September 17, 2007

History of Aerosol Science

The first time my interest in aerosol science picked up was when I learnt about nuclear winter -- a phenomena which refers to possible climatic impact of all-out nuclear war. What really fascinated me was the idea that if one wants to control climate or weather in predictive manner, aerosols are going to be the best tool; for a reason that they have relatively short life-time giving control over their introduction and removal in the atmosphere. Well! this is not the subject of today's post. Thinking of my own interests in this field led me to think about history of aerosol science. Couple of years before I read Spencer Weart's "The Discovery of Global Warming". I am fascinated by its content and writing style. Experience was not less than reading suspense thriller. Later on, I come across a comment that book is weighted toward contributions of American scientists than European scientists. I do not know the truth as my knowledge in the history of climate science is limited. But if asked Weart's book is my first recommendation.

The climate scientist J. Murray Mitchell, Jr. took up the question, with the help of improved data on how minuscule particles (aerosols) moved through the upper atmosphere. Studies of fallout from nuclear bomb tests had shown that fine dust injected into the stratosphere would linger for a few years, but would not cross from one hemisphere to the other. With that in mind, Mitchell pored over global temperature statistics and put them alongside the record of volcanic eruptions. In 1961, he announced that large eruptions caused a significant part of the irregular variations in average annual temperature in a given hemisphere. On the other hand, average temperatures had fallen since 1940, a period in which the world had seen few major eruptions. Mitchell concluded that the recent cooling was an "enigma." He thought it might signal a new phase of a decades-long "rhythm," the sort of cycle that generations of climatologists had tried to winkle out of their data
While thinking of Weart's book, I started searching what resources are available on Internet about history of aerosol science and to my delight I found that Weart has created web-pages to supplement his book. On his web-page you can read history of aerosol science and global warming with full references, illustrations and pictures of scientists. A link is available to download whole web-site in zip file so one can burn his/her own CD, or one can download PDF file and print it and of cause one can read it online. Following is the link to table of content.

Climate Change: Discovery of Global Warming

Thursday, September 6, 2007

Treating Dust As A Spherical Particle: Good/Bad Assumption?

It is widely know that dust is essentially non-spherical and hence radiative transfer calculations treating dust as a spherical particle are not adequate. A recent laboratory based study on dust particles by Jingmin Li and Kazuo Osada is very interesting. This article appeared in GRL this month. They study the preferential setting of elongated mineral dust collected from snow in a high mountain in Japan. The positions of particles' centers of gravity and folding centers are analyzed using a scanning electron microscopy and optical microscopy. Their results suggest that a preferential orientation exists for particles settling heavy side down (as expected) but what is interesting is the analysis of results from Ginoux's model wherein they apply this preferential orientation information and show that : " away from the source regions, dust particles are essentially spherical, which considerably simplify the calculation of settling velocity in transport and of radiative transfer models."

Figure above shows the relative difference of calculated settling velocity between ellipsoidal and spherical particles {Δu∞ = 100% × [u∞ (λ) − u∞ (λ = 1)]/u∞ (λ = 1)}. For example, the settling velocity of particles of 2 μm diameter increases respectively around 50%, 100%, and 165% for aspect ratios of 2, 4, and 10. The relative difference decreases with increasing particle size. For particles of 10 μm, the settling velocity increase for ellipsoids is around 30–40%, with little difference shown for aspect ratios of 1–10. On the other hand, a 40% decrease of settling velocity for ellipsoids is apparent at around 40–50 μm for the aspect ratio of 10.

Reference :

Li, J., and K. Osada (2007), Preferential settling of elongated mineral dust particles in the atmosphere, Geophys. Res. Lett., 34, L17807, doi:10.1029/2007GL030262.