C. Matsoukas

Climatology and trends of aerosol optical depth over the Mediterranean basin during the last 12 years (2002–2014) based on Collection 006 MODIS-Aqua data

The Mediterranean basin is a region of particular interest for studying atmospheric aerosols due to the large variety of air masses it receives, and its sensitivity to climate change. In this study we use the newest collection (C006) of aerosol optical depth from MODIS-Aqua, from which we also derived the fine-mode fraction and Ångström exponent over the last 12years (i.e., from 2002 to 2014), providing the longest analyzed dataset for this region. The long-term regional optical depth average is 0.20±0.05, with the indicated uncertainty reflecting the inter-annual variability. Overall, the aerosol optical depth exhibits a south-to-north decreasing gradient and an average decreasing trend of 0.0030 per year (19% total decrease over the study period). The correlation between the reported AOD observations with measurements from the ground AERONET stations is high (R=0.76-0.80 depending on the wavelength), with the MODIS-Aqua data being slightly overestimated. Both fine-fraction and Ångström exponent data highlight the dominance of anthropogenic aerosols over the northern, and of desert aerosols over the southern part of the region. Clear intrusions of desert dust over the Eastern Mediterranean are observed principally in spring, and in some cases in winter. Dust intrusions dominate the Western Mediterranean in the summer (and sometimes in autumn), whereas anthropogenic aerosols dominate the sub-region of the Black Sea in all seasons but especially during summer. Fine-mode optical depth is found to decrease over almost all areas of the study region during the 12-year period, marking the decreasing contribution of anthropogenic particulate matter emissions over the study area. Coarse-mode aerosol load also exhibits an overall decreasing trend. However, its decrease is smaller than that of fine aerosols and not as uniformly distributed, underlining that the overall decrease in the region arises mainly from reduced anthropogenic emissions.

Aerosol shortwave direct radiative effect and forcing based on MODIS Level 2 data in the Eastern Mediterranean (Crete)

A spectral radiative transfer model was used to quantify the aerosol direct radiative effect and forcing over the island of Crete in the Eastern Mediterranean. Computations were performed for the 11-year period from 2000 to 2010. MODIS Level 2 data (daily, 10 km × 10 km spatial resolution) were used as input to the model. Output includes the radiative fluxes and the aerosol direct radiative ffect at the top of the atmosphere, within the atmosphere and at the surface. The corresponding forcing components were evaluated based on MODIS fine mode aerosol data. Results show a decreasing trend of the aerosol radiative effect. The analysis of the contribution of anthropogenic and natural aerosols shows major peaks of natural aerosol effects occurring mainly in spring and autumn, while a summer maximum is attributed to anthropogenic aerosol.

Direct Effect of Aerosols on Solar Radiation Over the Eastern Mediterranean Basin on a Daily 1° by 1° Resolution

The climatically sensitive Mediterranean basin, which is characterized by high solar radiation amounts and aerosol loadings, is the focus of this study that aims to determine the direct effect of aerosols on solar radiation (DRE) over the eastern basin. The objective is to reveal detailed patterns of aerosol DRE that are smoothed when obtained at coarse resolution. Therefore, computations of DRE are performed at a concurrent spatial and temporal resolution that has not been achieved to date. The DREs are computed for 1×1° latitude-longitude grids with the FORTH detailed spectral radiative transfer model (RTM) using daily input data for various atmospheric and surface parameters, such as clouds, water vapor, ozone and surface albedo, taken from the NASA-Langley Global Earth Observing System database. Key aerosol optical properties, namely aerosol optical depth, single scattering albedo and asymmetry parameter, necessary for the RTM runs, are taken from combined climatologies, like the Global Aerosol Data Set, and the satellite-derived datasets of Total Ozone Mapping Spectrometer and Advanced Very High resolution Radiometer that satisfy daily availability at the RTM required spectral and 1×1° resolution. The aerosol DREs are computed at the surface, the top-of-atmosphere and within the atmosphere, over the period 1985–1995.

Study of the Total and Ultraviolet Solar Radiation in the Alpine Region of Ioannina (Northwestern Greece)

The FORTH deterministic spectral radiative transfer model is used to estimate the incoming surface solar radiation (ISSR) at the alpine city of Ioannina in northwest Greece. The model is initialized with high spatial (10 km × 10 km and 5 km × 5 km) and temporal (daily) resolution satellite Level-2 Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) data for aerosol, cloud and other atmospheric and surface parameters. The daily total and ultraviolet (UV) solar radiation is computed with the model for the period 2008–2012. The model ISSR is successfully validated against corresponding ground-based measurements of total and UV radiation from a station located at Ioannina for the study period. The instantaneous total, UVA and UVB ISSR values are as high as 1070, 45 and 2.25 W/m2 in summer, exhibiting a significant day to day and seasonal variability, primarily driven by the top of atmosphere solar radiation and clouds. The primary role of clouds for ISSR, versus aerosols and ozone, is also verified by model sensitivity tests, which reveal however an increasingly stronger role of these two parameters for UV radiation.

Cloud Radiative Effects on Solar Radiation Over the Eastern Mediterranean Basin from 1984 to 2007

The cloud radiative effect (CRE) on solar shortwave (SW) radiation is investigated over the broader Mediterranean basin, for the 24-year period from 1984 to 2007, using a deterministic spectral radiation transfer model (RTM) and quality monthly cloud data taken from the ISCCP-D2 satellite database. The model simulates the interaction of solar radiation with all relevant physical parameters, namely ozone, carbon dioxide, methane, water vapour, aerosols and atmospheric molecules as well as surface reflection. The ISCCP cloud model input data include cloud cover and optical depths for low-, mid-, and high-level clouds, separately for ice and liquid water clouds. The model computes CREs at the top of atmosphere (CRETOA), within the atmosphere (CREatmab), and at the surface (effects on downwelling and absorbed solar radiation, CREsurf and CREsurfnet). The determined perturbation of regional SW radiation budget by clouds is important, undergoing significant intra-annual and inter-annual changes.

Reply to comment by Kara and Barron on “Seasonal heat budgets of the Red and Black seas”

] We appreciate the chance to present our views on thecomment by Kara and Barron [2008] and contribute to thediscussion that began. The criticism raised by Kara andBarron [2008] focuses onthree issues: The first issue, whichalso draws most of their attention, is the representativenessof the coarse-resolution reanalysis used in our original paper[Matsoukas et al., 2007]. The second issue is our use ofmonthly temporal resolution, instead of, e.g., 6-hourlyproducts. Finally, the third issue deals with the calculationof the exchange coefficients in the parameterization of thelatent and sensible heat fluxes. In this Reply, we will try toaddress each issue separately, and then give our generalopinion on the Conclusions of Kara and Barron [2008].[