... Matsoukas (1), Antonis Gkikas (3), Christos Papadimas (2), and Andy Sayer (4), ... Reagan, 30 J. A., Kaufman, Y., Nakajima, T., Lavenu, F., Jankowiak, I., and ...
The regime of aerosol asymmetry parameter and Angstrom exponent over Europe, Mediterranean and Middle East based on MODIS satellite data. Intercomparison of MODIS-Aqua C051 and C006 retrievals (1)
Marios Bruno Korras-Carraca , Nikolaos Hatzianastassiou (2), Christos Matsoukas (1), Antonis Gkikas (3), Christos Papadimas (2), and Andy Sayer (4), (5) Department of Environment, University of the Aegean, Mytilene 81100, Greece, (2) Laboratory of Meteorology, Department of Physics, University of Ioannina, 45110 Ioannina, Greece, (3) Barcelona Supercomputing Center, Barcelona, Spain, (4) NASA Goddard Space Flight Center, Greenbelt, MD, USA, (5) Goddard Earth Sciences Technology And Research (GESTAR), Universities Space Research Association, Columbia, MD, USA (1)
GEOGRAPHICAL DISTRIBUTIONS MODIS-AQUA C051
MODIS-AQUA C006
ASYMMETRY PARAMETER 660 nm
SUMMARY – DATA
ANGSTROM EXPONENT 870 nm
550-865 nm
Atmospheric aerosols, both natural and anthropogenic, can cause climate change through their direct, indirect, and semi-direct effects on the radiative energy budget of the Earth-atmosphere system (Hatzianastassiou et al. 2004). In the present work, we study two of the most important optical properties of aerosols, the asymmetry parameter (gaer) and the Angstrom exponent (α). Both gaer and α are related with aerosol size, which is a very important parameter for climate and human health. ● The study region comprises North Africa, the Arabian peninsula, Europe, and the Mediterranean basin (5° - 70° N, 25° W - 60° E). These areas are of great interest, because of the variety of aerosol types they host, both anthropogenic and natural. Urban, industrial or biomass-burning aerosols are usually fine, while desert dust or sea-salt are basically coarse, making thus possible the establishment of a relationship between the type and the size of aerosols. ● Using satellite data from the collection 051 of MODIS (MODerate resolution Imaging Spectroradiometer, Aqua, Remer et al., 2008), we Investigate the spatio-temporal characteristics of the asymmetry parameter and Angstrom exponent. An intercomparison between collection 051 and the most recent collection (006) as well as against surface AERONET (Aerosol Robotic Network) measurements (Holben et al., 1998) is also performed. ➔Study period: 4 July 2002 to 18 September 2010 ●
550-865 nm
JANUARY
ANNUAL
470 nm
COMPARISON WITH AERONET
We generally find significant spatial variability, with larger g aer values over regions dominated by larger size particles, e.g. outside the Atlantic coasts of north-western Africa, where desert-dust outflow is taking place. The gaer values tend to decrease with increasing wavelength, especially over areas dominated by small particulates. The intra-annual variability is found to be small in desert-dust areas, with maximum values during summer, while in all other areas larger values are reported during the cold season and smaller during the warm. Significant intra-annual and interannual variability is observed around the Black Sea. However, the inter-annual trends of gaer are found to be generally small. ● The geographical distributions for α (given for the pair of wavelengths 550-865 nm) affirm the conclusions drawn from the asymmetry parameter as regards the aerosol size over the study region, with larger α values in regions where the aerosol load is dominated by fine particles.
Figure: AERONET stations within our study region
Table 1: Mean bias, root mean squared error (RMSE) and the correlation coefficients (R), values of applied linear regression fits between MODIS and AERONET data. PARAMETER, (COLLECTION)
JULY
APRIL
●
SLOPE (2002-2010) *
OCTOBER
Intercomparison of MODIS-Aqua C051 and C006 retrievals
BIAS **
BIAS %
R (Pearson)
We compare satellite data with surface data from the AERONET, in order to validate the reliability of the former. ● Generally, we find a moderate agreement between satellite asymmetry parameter data at 470 nm and surface data at 440 nm, with small correlation coefficient. Slightly better agreement at larger wavelengths. ● Moderate agreement between satellite and surface Angstrom exponent data, with an underestimation of aerosol size from MODIS (larger α values). This underestimation is smaller in collection 006. ● The main results of MODIS-AERONET comparison are summarized in table 1.
ASYMMETRY PAR. (C051) ANGSTROM EXP. (C051) ANGSTROM EXP. (C006)
WAVELENGTH MODIS (AERONET) 470 nm (440 nm) 660 nm (675 nm) 870 nm (870 nm) 550-865 nm (550-865 nm) 550-865 nm (550-865 nm)
BIAS *
RMSE
R
-0.018 0.005 0.015 0.111 0.031
0.047 0.062 0.072 0.403 0.384
0.27 0.42 0.46 0.61 0.64
* MODIS-AERONET
REFERENCES Hatzianastassiou, N., Katsoulis, B., and Vardavas, I.: Sensitivity analysis of aerosol direct radiative forcing in ultraviolet – visible wavelengths and consequences for the heat budget, Tellus, 20 56b, 368–381, 2004. Holben, B. N., Eck, T. F.,Slutsker, I., Tanré, D., Buis, J. P. , Setzer, A., Vermote, E., Reagan, 30 J. A., Kaufman, Y., Nakajima, T., Lavenu, F., Jankowiak, I., and Smirnov, A.: AERONET – A federated instrument network and data archive for aerosol characterization, Remote Sens. Environ., 66, 1–16, 1998. Levy, R. C., Mattoo, S., Munchak, L. A., Remer, L. A., Sayer, A. M., Patadia, F., and Hsu, N. C.: The Collection 6 MODIS aerosol products over land and ocean, Atmos. Meas. Tech., 6, 2989-3034, doi:10.5194/amt-6-2989-2013, 2013. Remer, L. A., Kaufman, Y. J., Tanré, D., Mattoo, S., Chu, D. A., Martins, J. V., Li, R.-R., Ichoku, 15 C., Levy, R. C., Kleidman, R. G., Eck, T. F., Vermote, E., and Holben, B. N.: The MODIS aerosol algorithm, products, and validation, J. Atmos. Sci., 62, 947–973, 2005.
** C006 - C051
A daily Angstrom exponent intercomparison is performed between collection 051 and the most recent collection (006). Our results reveal a good agreement between the two datasets, with a correlation coefficient ranging between 0.75 and 0.95 above the study region. ● Moreover generally small Angstrom exponent trends are found in both collections. The trends mainly do not change from C051 to C006. ●
yr -1
* deseasonalized
yr -1
yr -1
yr -1
yr -1
ACKNOWLEDGEMENT This research has been co‐financed by the European Union (European Social Fund – ESF) and Greek national funds through the Operational Program "Education and Lifelong Learning" of the National Strategic Reference Framework (NSRF) Research Funding Program: THALES. Investing in knowledge society through the European Social Fund.
