Below are plots of radiosonde/SYNOP BUFR coverage for 30 May 2014 - reports as decoded at ECMWF, some reports not in standard BUFR are not decoded.
(Grey: TAC reports but no BUFR, Green: BUFR reports but no TAC, Red *: position error. Light/dark blue indicates that there are less/more than 60% of the reports available in BUFR. Counting reports is more problematic for radiosondes, in some cases eg South Africa there are more TAC reports because both TEMP and PILOT are produced from the same ascent.)
Radiosonde coverage (about 45% of stations report in BUFR, but most - apart from the dark blue stations in the plot - report reformatted TEMP, see "structure" page):
Synop coverage (over 60% of stations report in BUFR):
