I am not writing something new and am not the first time to write about it. But at the 3rd of this month there was clearly a evidence that propagation between Europe and Japan, Korea and China is not ES or sporadic-E. The 3rd of July PA0O Jaap wrote it in his blog that propagation was very good and he made his first QSO with China on JT65.At the same date there were very strong PMSEs (Polar Summertime Mesoshperic Echoes) measured at 56MHz from Norway. These echoes are related to NLCs (Noctilucent Clouds) which can be seen here in Europe at the evening just after sunset if you're lucky!
Years ago JE1BMJ discovered SSSP (Summer Solstice Shortpath Propagation) and named it like that after the translation help of G3WOS. You can read about SSSP in relation to PMSEs in this 2006 publication. If you like the ride the SSSP waves you can read Han's tips on radio and especially antennas in this publication as well. However, 10 years ago you really needed a big yagi and some power to explore the SSSP, these days with the use of JT modes it is theoretically possible to make a QSO via SSSP with a high enough vertical and 50W.
Noctilucent clouds seems to be getting stronger each year as it is believed CFCs, methane and carbon dioxide are contributing to forming these clouds. You can find a nice research here.
G3XBM Roger has been writing about this several times on his blog and you can read the following on his website about this:
NLCs typically appear about 20 days prior to the summer solstice, increase quickly to a high summer level, and then disappear about 50 days after the summer solstice. These clouds are mostly a high latitude phenomenon, and are believed to be composed of ice crystals. VHF radars see very strong echoes from these clouds, and since they are at mesospheric heights (80 to 90 km), they are also known as polar mesosphere summer echoes (PMSE). These clouds are hypothesized by JE1BMJ and others to be responsible for 6m propagation across high latitudes (for example, from the East Coast of North America to Japan) during the northern hemisphere summer. This mode of propagation has been dubbed Summer Solstice Short-path Propagation (SSSP).