what about the ISCCP data?, it is available from NASA GISS, I assume they have daily data also

The best dataset for cloud cover is those derived from Calipso/Cloudsat satellites like GOCCP, but it gives incomplete spatial data from local instantaneous fields. Otherwise, ISCCP is good for sub-daily time scales with global coverage. Which time period do you want? Where?

I think Landsat8 data will be useful for you. Correct me if I am wrong .

Do you need global data or just over a specific region? Sub-daily cloud cover from satellites is very difficult. If you go to GIOVANNI:

http://giovanni.sci.gsfc.nasa.gov/giovanni/

You will notice that the only sub-daily cloud-fraction product is actually from MERRA reanalysis. Most of the satellites products will only give you one snapshot per day. For instance, Calipso carries a Lidar and hence the swath is very narrow, and as the A-Train has a polar orbit it takes about 15 days to cover the whole globe. Moreover, polar-orbit satellites only passes twice over the same place every day.

As you need sub-daily data, you can't escape from looking at geostationary satellites, like GOES, or something like the PR onboard of TRMM. Or a combination of satellites, like done in ISCCP. However, ISCCP is only 1983-2009 and is a very old product with many issues. You should check the relevant literature to see if these would affect what you want to do with such dataset. 

Another option would be to derive your own cloud cover estimator. For instance, if you take GOES radiances (every 15min or 30min), calculate the brightness temperature and then set some threshold to eliminate the ground pixels and count just those cold pixels that should be clouds. See for instance DOI:10.1175/JAMC-D-15-0229.1 and the references therein.

 My personal favorite that give you world-wide coverage of the oceans is the"Infrared NHC Enhancement" images from http://tropic.ssec.wisc.edu/real-time/imagemain.php?&basin=europe&sat=m7&prod=irn and you get the different parts of the planet by going to the "Basins" box in the upper right hand corner. 

Then for worldwide cloud coverage that changes every six hours, I open my computer to http://www.ssec.wisc.edu/data/comp/latest_cmoll.gif each morning.

Then for tropical storms if you start at http://rammb.cira.colostate.edu/products/tc_realtime/  --then when you click on a particular storm like Typhoon HAIMA they have 32 different methods they use to image those storms at http://rammb.cira.colostate.edu/products/tc_realtime/storm.asp?storm_identifier=WP252016 that image every 4 hours.

Out of those 32 image methods, my personal favorite are the movies you can watch with the loops from the "Storm Relative 16 km Geostationary Water Vapor Imagery"  at http://rammb.cira.colostate.edu/products/tc_realtime/archive.asp?product=16kmgwvp&storm_identifier=WP252016

Also what might be useful for your purposes are the "Enhanced Infrared (IR) Imagery (1 km Mercator, MODIS/AVHRR)" and the "Enhanced Infrared (IR) Imagery (4 km Mercator)" and perhaps the "Enhanced Infrared (IR) VIIRS"?

MODIS atmosphere group provides cloud mask and cloud properties data. The subdaily L2 data comes on 1km grid and can be ordered via https://ladsweb.nascom.nasa.gov/search/index.html

Look for `Aqua Atmosphere Level 2 products` >`MYD35_L2` product name in the selection menu.

https://ladsweb.nascom.nasa.gov/search/index.html

Also, depending on what period and area you are interested in, MSG based cloud properties product from Climate Monitoring SAF could be helpful, according to the product description it contains hourly estimates along with daily and monthly products.

https://wui.cmsaf.eu/safira/action/viewDoiDetails?acronym=CLAAS_V001

Hi,

See:  Calipso/Cloudsat application and  Landsat8 data.