The Cloud Makers - A video about effect of aerosols on cloud

I found a very interesting video about effects of aerosols on clouds and how the GLORY mission of NASA going to address this problem. Click on the image or the link below to view the video.



Play video "The Cloud Makers"

Image courtesy: NASA Goddard Space Flight Center

Long Range Transport of Dust Aerosols

Continuing from our last blog post on the issue of aerosol radiative forcing (ARF) and the importance of its vertical distribution, l would like to bring to attention another important aspect associated with aerosols that affect global ARF. This aspect is the transport of aerosols which is very closely related to its vertical distribution. One of the largest sources of aerosols is desert. These desert dust aerosols have gained much attention due to the long range transport associated with them. The dust from these deserts is lifted higher in the atmosphere and ‘because of the fast large-scale transport in the upper troposphere, aerosols such as dust and black carbon, once they enter the upper troposphere (above ~8 km), can be transported around the earth in a latitudinal belt in a week or two’. ‘The impact of long range transport of dust and air pollution from their continental sources over oceanic regions is one of the outstanding problems in understanding regional and global climate change’ and in also determining the air quality of regions to which dust is advected to. Using Calipso and surface micropulse lidar, Huang et al., [2008] observe the long-range transport and vertical distribution of Asian dust aerosols during the PACific Dust EXperiment (PACDEX). ‘The MPL measurements were made at the Loess Plateau (35.95°N, 104.1°E) near the major dust source regions of the Taklamakan and Gobi Deserts’ in China during March-May 2007. They find that ‘Dust events were more frequent in the Taklamakan, where floating dust dominates, while more intensive, less frequent dust storms were more common in the Gobi region. The vertical distribution of the CALIPSO backscattering/depolarization ratios indicate that non-spherically shaped dust aerosols floated from near the ground to an altitude of approximately 9 km around the source regions. This suggests the possible long-range transport of entrained dust aerosols via upper tropospheric westerly jets. A very distinct large depolarization layer was also identified between 8 and 10 km over eastern China and the western Pacific Ocean corresponding to dust aerosols transported from the Taklamakan and Gobi areas, as confirmed by back trajectory analyses. The combination of these dust sources results in a two-layer or multilayered dust structure over eastern China and the western Pacific Ocean.’ We have seen in our last blog spot that ‘the vertical distribution of dust aerosols is another critical factor impacting the effects of dust on radiative forcing and climate [Claquin et al., 1998; Zhu et al., 2007; Forster et al., 2007].

References:

Huang, J., P. Minnis, B. Chen, Z. Huang, Z. Liu, Q. Zhao, Y. Yi, and J. Ayers (2008), Long-range Transport and Vertical Structure of Asian Dust from CALIPSO and Surface Measurements during PACDEX, J. Geophys. Res., doi:10.1029/2008JD010620, in press.

Claquin, T., M. Schulz, Y. J. Balkanski, and O. Boucher (1998), Uncertainties in assessing radiative forcing by mineral dust, Tellus, Ser. B, 50, 491–505.

Forster, P., V. Ramaswamy, P. Artaxo, T. Berntsen, R. Betts, D.W. Fahey, J. Haywood, J. Lean, D.C. Lowe, G. Myhre, J. Nganga, R. Prinn,G. Raga, M. Schulz and R. Van Dorland (2007), Changes in Atmospheric Constituents and in Radiative Forcing. In: Climate Change 2007: The Physical Science Basis. contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

Zhu, A., V. Ramanathan, F. Li, and D. Kim (2007), Dust plumes over the Pacific, Indian, and Atlantic oceans: Climatology and radiative impact, J. Geophys. Res., 112, D16208, doi:10.1029/2007JD008427

Impact of Aerosol Vertical Distribution on their Radiative Effects

From over a decade of aerosol research, it is now a well established fact that atmospheric aerosols play a crucial role in altering the earth's radiation budget [IPCC 2007]. Toa large extent, the effect on aerosols on the top-of-atmosphere radiation balance has been addressed using both observations and global models. A close review of literature suggests the imperative need to address the vertical distribution of aerosols in the atmosphere [Gadhavi et al., 2006] and that is exactly what aerosol science is gearing towards. Recently, there have been many research studies that have begun to address this question. One interesting paper by Johnson et al., appeared in JGR last week that talks about this very issue.

This paper provides very good insights into this topic by using ground and aircraft based lidar observations during DABEX field campaign. 'In general, mineral dust was observed at low altitudes (up to 2 km), and a mixture of biomass burning aerosol and dust was observed at altitudes of 2–5 km.'

For clear sky conditions, when the observed low-level dust layer was included in a radiative transfer model, the absorption of solar radiation by the biomass burning aerosols increased by 10%.' This enhancement in absorption is due to reflection of solar radiation by dust aerosols in background up into the biomass burning aerosol layer above. This situation is analogous to presence absorbing aerosols over a bright background. Thus, depending on the distribution of aerosols and the type of aerosols present at different heights in the atmosphere, their radiative effects can be altered. This in-turn changes the differential heating of the atmosphere and hence the atmospheric stability that influences convective and turbulent motions and clouds [Ackerman et al., 2000]. This can be important for both TOA and surface radiation budget. The scenario is a little more complex when aerosols are above clouds. 'For example, the elevation of biomass burning aerosols above marine stratocumulus clouds during the Southern African Regional Science Initiative (SAFARI-2000) greatly enhanced their absorption of shortwave radiation. This led to a positive direct aerosol shortwave radiative effect over the Southern Atlantic, whereas the effect was negative in clear sky conditions [Keil and Haywood, 2003; Abel et al., 2005; Myhre et al., 2003a]'. Thus, the need to consider the treatment and appropriate representation of vertical distribution of aerosol species in the global models when estimating the impact of anthropogenic absorbing aerosols is crucial.

Please refer to the paper by Johnson et al (below) for all references in this blog-post:

Johnson, B. T., B. Heese, S. A. McFarlane, P. Chazette, A. Jones, and N. Bellouin (2008), Vertical distribution and radiative effects of mineral dust and biomass burning aerosol over West Africa during DABEX, J. Geophys. Res., 113, D00C12, doi:10.1029/2008JD009848

Principal components analysis (PCA) for source identification

Source identification for atmospheric aerosol is important for developing effective strategy to reduce their emissions. One of the methods for source identification is principal components analysis (PCA). My attention was drawn to this method recently first through a review article about methods and results for aerosol source apportionment over European region and then through the article “Identification of PM sources by principal component analysis (PCA) coupled with wind direction ”. Dr. Viana Rodríguez, Mª del Mar is the lead author on both the articles . She is a researcher at the Institute of Earth Sciences Jaume Almera, Spain.

Application of the principal components analysis method for aerosol is based on the foundation that each source has unique blending of various aerosol components. Variability of the components is strongly correlated among themselves when they are coming from same source when compared to a case where they are coming from heterogeneous sources. Mathematically, PCA seeks to determine matrices A and S in the equation C=A∙S, where column matrix C represents concentration of various particulate matter (PM) components, S is the source contribution and A is the source profiles.

The article Viana et al. (2006) is more about results obtained using PCA analysis rather than the method itself. I liked the article for its clear conclusions and bold figures. I think figure 1 will be useful for those who are interested in knowing typical combination of various aerosol sources for given total mass. Figure 4 will be very useful for the people of the town Llodio, for knowing where to look for reducing pollution. I have recreated images for quick look using data from the manuscript.

References:

Viana, M., et al., (In Press), Source apportionment of particulate matter in europe: A review of methods and results, Journal of Aerosol Science, Accepted Manuscript.

Viana, M., X. Querol, A. Alastuey, J. I. Gil, and M. Menéndez (2006, December),Identification of pm sources by principal component analysis (pca) coupled with wind direction data, Chemosphere 65 (11), 2411-2418.

Aerosol Radiative Effects over Global Land: A Satellite based Study

GRL published an article on estimation of aerosol radiative effects over global land using purely observations from Terra satellite on February 22, 2008. Although, I am one of the co-author in the paper but I would like to congrats Falguni Patadia, first author of the paper for her research, which is first attempt in certain ways. This paper presents the estimation of top of the atmosphere (TOA) short wave aerosol radiative effects over global land areas for each half degree by half degree grid point. The uniqueness of the study comes from the fact that it is purely observation based study, which does not involve any complex radiative transfer and/or climate model runs. Results of the study are encouraging and matches very well with other purely model or hybrid (model and observations) type of studies. This research used one year worth of satellite observations of TOA fluxes derived from CERES broadband instrument, MODIS high resolution cloud masks and MISR derived aerosol optical thickness data sets to perform the analysis. As we all know that, aerosol impacts in climate change studies in one of the most uncertain component and level of scientific understanding about this component is very low. This study is certainly a good start and will help to understand aerosol effects on earth-atmosphere radiation budget. For more details on the results and methodology, please refer the publication and if you do not have access to the article, we will be happy to share reprints with you.


Complete Reference:

Patadia, F., P. Gupta, and S. A. Christopher (2008), First observational estimates of global clear sky shortwave aerosol direct radiative effect over land, Geophys. Res. Lett., 35, L04810, doi:10.1029/2007GL032314