## 2 Data and Methods  
### Data  
#### 2.1.1 MODIS/Aqua Aerosol  
Cloud, and Water Vapor Measurements  
A core product of this research is the Moderate Resolution Imaging Spectroradiometer onboard Aqua satellite (MODIS/Aqua) collection 6.1 (C6.1) level-2 joint atmosphere product (MYDATML2). More specifically, single-pixel AOD\({}_{500}\), cloud optical, microphysical and macrophysical properties, and water vapor column data retrieved from the MODIS/Aqua satellite sensor [33] were acquired for the period 2005-2019. Aqua, part of the A-train satellite constellation, has been flying at a sun-synchronous polar orbit at 705 km above the Earth since May 2002. MODIS/Aura is characterized by a wide spectral range (0.41 \(\upmu\)m to 14.5 \(\upmu\)m in 36 channels or bands), a broad swath (2330 km) and a spatial resolution of 250, 500 and 1000 m (depending on band), providing almost daily global coverage. MODIS/Aqua crosses Greece, which is our focus area here, at around 11:30 UTC.  
The AOD\({}_{500}\) retrievals used in this work are part of the merged \"Dark Target\" and \"Deep Blue\" algorithm dataset (AOD_550_Dark_Target_Deep_Blue_Combined) having a spatial resolution of 10 km \(\times\) 10 km at nadir. AOD\({}_{500}\) is retrieved by two different DT algorithms, one for vegetated and dark-soiled surfaces [34; 35; 36; 37], and one for oceanic areas [35; 37; 38]. DB is currently applied over all the continental areas while it was originally built for bright continental surfaces, where DT fails [39; 40; 41; 42]. Validation of the C6.1 DT product showed that the expected error (EE) is \(\pm\)(0.05 + 0.15\(\uptau_{\rm A}\)) over land, and +(0.04 + 0.1\(\uptau_{\rm A}\)), \(-\)(0.02 + 0.1\(\uptau_{\rm A}\)) over the sea [37] (\(\uptau_{\rm A}\): optical thickness retrieved from sun photometric measurements from the AErosol RObotic NETwork known as AERONET). Over arid,bright, or urban surfaces the C6.1 DB EE is around \(\pm\)(0.03 + 21%) and over vegetated surfaces around \(\pm\)(0.03 + 18%) [43; 44].  
For clouds, the following cloud optical, microphysical, and macrophysical properties from MODIS/Aqua C6.1 [45] were acquired: cloud fraction (Cloud_Fraction; CF), cloud phase (Cloud_Phase_Optical_Properties; CP), cloud optical thickness (Cloud_Optical_thickness; COT), cloud effective radius (Cloud_Effective_Radius; CER) and cloud top pressure (Cloud_Top_Pressure; CTP). CF is determined from the 1 km MODIS pixels, which are identified as cloudy and probably cloudy from the cloud mask product [46; 47; 48; 49], and is given at a spatial resolution of 5 km \(\times\) 5 km along with the other cloud properties. The C6.1 CP used here is retrieved by the daytime-only algorithm that uses a combination of visible (VIS), shortwave infrared (SWIR), and infrared (IR) channels ([PERSON] et al. [50] and references therein for details). The cloud optical and microphysical product algorithm makes use of six VIS, near-IR (NIR), SWIR, and mid-wave IR (MWIR) MODIS channels, as well as several thermal IR channels [45]. COT and CER are retrieved simultaneously based on the bispectral solar reflectance method [51]. CTP is retrieved by the cloud top properties algorithm, which relies on CO\({}_{2}\)-slicing channels (13-14 \(\upmu\)m spectral region) and two IR window channels [52; 53].  
In addition to aerosol- and cloud-related parameters, total column precipitable water (Precipitable_Water_Near_Infrared_ClearSky; PW) data from the MODIS NIR algorithm [47] were acquired. The algorithm makes use of the ratios of water vapor absorbing bands (within the 0.94 \(\upmu\)m water vapor band) with atmospheric window bands at 0.86 and 1.24 \(\upmu\)m. The data are also available at a 5 km \(\times\) 5 km spatial resolution.