Tuesday, April 24, 2007

Jim Hansen receives Dan David Prize

The DAN DAVID PRIZE annually awards 3 prizes of US$ 1 million each for achievements having an outstanding scientific, technological, cultural or social impact on our world. Each year fields are chosen within the three Time Dimensions - Past, Present and Future. Another interesting fact about Dan David Prize is that recipients donate 10% of their prize money to graduate students in their respective field.

The 2007 Dan David Prize honors Dr. James Hansen for his significant contributions in the field of "Quest for Energy". He will be sharing the award with Sarah Kurtz and Jerry Olson.

James Hansen is a towering figure in atmospheric aerosol research. His paper with Lacis in Nature (doi:10.1038/346713a0) has been used by many to show the importance of atmospheric aerosols in earth's radiation budget. I was so impressed by his paper with Menon, Nazarenko and Luo in Science (doi:10.1126/science.1075159) about climatic effect of black carbon in China and India that I decided to pursue it further during my tenure as post doctoral research fellow at Physical Research Laboratory.

Dan David Prize recognizes James Hansen for his seminal contribution for (a) understanding of the various forces that govern Earth's radiation budget whereby increasing amounts of trace gases and aerosols in the atmosphere prevent the escape of terrestrial infrared energy, thereby causing the planet to warm; (b) understanding the changes to Earth's energy balance through large scale calculations with general circulation models and studies of paleoclimatic data; and (c) quantitative assessment of global thermometric records to document changes in Earth's mean surface temperature in response to these energy restrictions. These calculations confirm the natural greenhouse effect of about 32 degrees C that was already in existence prior to the Industrial Revolution, and the augmented effect of about 0.8 degrees C from the atmospheric concentration increases observed during the late 20th Century for carbon dioxide, methane, nitrous oxide, and other gases and aerosols.

My heartiest congratulations to James Hansen for his well deserving achievement.

(1.) http://en.wikipedia.org/wiki/James_Hansen

(2.) http://www.columbia.edu/~jeh1/

(3.) http://www.dandavidprize.org/


* Hansen, J. E., and Lacis A. A. (1990), Sun and dust versus greenhouse gases: an assessment of their relative roles in global climate change, Nature, 346,713-719.

* Menon, S., J Hansen, L. Nazarenko, and Y Luo (2002), Climate Effects of Black Carbon Aerosols in China and India, Science, 297, 2250-2253.

Sunday, April 15, 2007

Global Aerosol Sources: Synergy of Satellite and Model

This paper by Dubovik et al., appeared online in Atmos. Chem. Phys. Discuss.

The abstract read as

"Knowledge of the global distribution of tropospheric aerosols is important for studying the effects of aerosols on global climate. Chemical transport models rely on archived meteorological fields, accounting for aerosol sources, transport and removal processes can simulate the global distribution of atmospheric aerosols. However, the accuracy of global aerosol modeling is limited. Uncertainty in location and strength of aerosol emission sources is a major factor in limiting modeling accuracy. This paper describes an effort to develop an algorithm for retrieving global sources of aerosol from satellite observations by inverting the GOCART aerosol transport model.
To optimize inversion algorithm performance, the inversion was formulated as a generalized multi-term least-squares-type fitting. This concept uses the principles of statistical optimization and unites diverse retrieval techniques into a single flexible inversion procedure. It is particularly useful for choosing and refining a priori constraints in the retrieval algorithm. For example, it is demonstrated that a priori limitations on the partial derivatives of retrieved characteristics, which are widely used in atmospheric remote sensing, can also be useful in inverse modeling for constraining time and space variability of the retrieved global aerosol emissions. The similarities and differences with the standard "Kalman filter" inverse modeling approach and the "Phillips-Tikhonov-Twomey" constrained inversion widely used in remote sensing are discussed. In order to retain the originally high space and time resolution of the global model in the inversion of a long record of observations, the algorithm was expressed using adjoint operators in a form convenient for practical development of the inversion from codes implementing forward model simulations.
The inversion algorithm was implemented using the GOCART aerosol transport model. The numerical tests we conducted showed successful retrievals of global aerosol emissions with a 2°×2.5° resolution by inverting the GOCART output. For achieving satisfactory retrieval from satellite sensors such as MODIS, the emissions were assumed constant within the 24 h diurnal cycle and aerosol differences in chemical composition were neglected. Such additional assumptions were needed to constrain the inversion due to limitations of satellite temporal coverage and sensitivity to aerosol parameters. As a result, the algorithm was defined for the retrieval of emission sources of fine and coarse mode aerosols from the MODIS fine and coarse mode aerosol optical thickness data respectively. Numerical tests showed that such assumptions are justifiable, taking into account the accuracy of the model and observations and that it provides valuable retrievals of the location and the strength of the aerosol emissions. The algorithm was applied to MODIS observations during two weeks in August 2000. The global placement of fine mode aerosol sources retrieved from inverting MODIS observations was coherent with available independent knowledge. This was particularly encouraging since the inverse method did not use any a priori information about the sources and it was initialized under a "zero aerosol emission" assumption. The retrieval reproduced the instantaneous global MODIS observations with a standard deviation in fitting of aerosol optical thickness of ~0.04. The optical thickness during high aerosol loading events was reproduced with a standard deviation of ~48%. Applications of the algorithm for the retrieval of coarse mode aerosol emissions were less successful, mainly due to the currently existing lack of MODIS data over high reflectance desert dust sources.
Possibilities for enhancing the global satellite data inversion by using diverse a priori constraints on the retrieval are demonstrated. The potential and limitations of applying our approach for the retrieval of global aerosol sources from aerosol remote sensing are discussed."

Complete reference of the article is

Dubovik, O., Lapyonok, T., Kaufman, Y. J., Chin, M., Ginoux, P., and Sinyuk, A.: Retrieving global sources of aerosols from MODIS observations by inverting GOCART model, Atmos. Chem. Phys. Discuss., 7, 3629-3718, 2007.

Update (2008-12-30)
The above reference is for discussion paper. The final version of paper can be found at following link.

Dubovik, O., Lapyonok, T., Kaufman, Y. J., Chin, M., Ginoux, P., Kahn, R. A., and Sinyuk, A.: Retrieving global aerosol sources from satellites using inverse modeling, Atmos. Chem. Phys., 8, 209-250, 2008.

Monday, April 9, 2007

Wikipedia's Role in Science Education and Outreach, EOS, Vol 88, Number 11, 13 March 2007

I ran into this article a while ago on EOS transactions (Vol 88, Number 11, 13 March 2007) and it made me pause and think on the message in the article. I thought it was something worth paying attention to and hence decided to post it here for us to contribute to the thought.
The purpose of the article was to inform the scientific community of the popularity of Wikipedia and to urge the experts in the community to take a look at the Wikipedia entry for one's area of expertise. The author raises concerns because of the fact that Wikipedia articles are encyclopedic by nature and so provide students with an apparently complete source of material for use in reports and research projects. The question then is: "how good is Wikipedia" in terms of completeness and accuracy? Are students learning the right things? To make Wikipedia as current and updated as possible in terms of information, it allows Anyone with internet connection to write an article about any topic or edit any existing article. This strength also becomes its weakness because the entries are anonymous and hence could lead to vandalism as well as articles by nonexperts. The article cites several examples to show how many articles in Wikipedia are very well written while others contain erros and misconceptions or are incomplete. Hence, the author urges the scientists to be familiar with how their fields are described on Wikipedia and, if interested, to write Wikipedia articles or edit articles that contain errors or are incomplete because that way scientists can play a role in education and public outreach realm.
Inspired from this article, I took a look at AEROSOL information on wikipedia and found that indeed this portion of the Wikipedia needs a lot of contribution in terms of completeness and referencing. For example, a definition on aerosols was found but there were no references that could lead to further reading on the definition. While Wikipedia mentions PM10 as particulate matter, there is no mention of PM2.5 or PM0.1. There is a statement that says " Averaged over the globe, anthropogenic aerosols—those made by human activities—currently account for about 10 percent of the total amount of aerosols in our atmosphere ". Such numbers must be backed with peer reviewed references.
Going on to my area of interest, I took a brief look at aerosol radiative information on Wikipedia. Again, this information was not complete for a novice reader/researcher. There are several landmark papers in this field that need to be appended in this section. The section briefly mentions the limitations of aerosol observation and hence the use of modeling in estimating global forcing. There is multitude of both regional and global aerosol forcing research based on observations and modeling that needs to be inculcated in this section and referenced. The widely popular topics of global warming and diming seem to be most updated on the Wikipedia. The completeness of which is again under a question mark. This section needs the attention of experts in this field because incomplete information could lead to misconceptions on this intricate subject.
The present article is written with an interest to promote the thought in the EOS article and their recommendations on contributing towards education and outreach.
Complete References :
Wikipedia's Role in Science Education and Outreach, EOS, Transcactions, AGU, Vol 88, Number 11, Pg 134-135, 13 March 2007

Monday, April 2, 2007

Heterogeneous Reactions among Sulfate, Nitrate and Mineral Dust aerosols and Radiative Forcing

People started quantifying the role of aerosol chemistry on radiative forcing. There is a nice study by Sussana Bauer from NASA about the effects of heterogeneous reactions among sulfate, nitrate and mineral dust aerosols on radiative forcing. Their modelling study (on global scale) suggest that the combined anthropogenic forcing of dust, nitrate and sulfate is -0.1 W/m2; however, excluding heterogeneous interactions leads to a 3 times larger negative forcing.

Full abstract:

Coating of mineral dust particles by air pollutants leads to core-mantle particles. These composite aerosols could interact differently with atmospheric radiation than the uncoated dust. In our simplified radiative calculations we assumed that a spherical dust core is covered uniformly by a liquid refractive material, such as sulfate or nitrate. Theoretical calculations of optical properties of such particles show that the single scattering albedo and the asymmetry parameter of core-mantle aerosols only differ significantly from uncoated dust if coating layers exceed 20% of the radius of the dust core. Global simulations of sulfate/nitrate-coated dust particles show that the thickness of the shell can be expected to range from 0 to 20% of the radius of the dust core. The result of this work is that mineral dust particles can be treated as external mixture within radiative calculations but the coating processes lead to changed loads in sulfate, nitrate, and mineral dust aerosol loads and therefore change their impact on Earth radiation. The combined anthropogenic forcing of dust, nitrate, and sulfate aerosols is -0.1 W/m2; however, excluding heterogeneous interactions leads to a 3 times larger negative forcing.


Bauer, S. E., M. I. Mishchenko, A. A. Lacis, S. Zhang, J. Perlwitz, and S. M. Metzger (2007), Do sulfate and nitrate coatings on mineral dust have important effects on radiative properties and climate modeling?, J. Geophys. Res., 112, D06307, doi:10.1029/2005JD006977.