First pic - lovely classic lenticular clouds caused by the airflow rising and falling after passing over high ground, rather like the way ripples form in a stream after the water has flown over a stone. Because of the clouds they are formed, they stay stationary as the air flows through them and yes - they have given rise to flying saucer reports.
They are much loved my glider pilots as the air is rising along the leading edge. If you can catch the lift it is usually strong and smooth and you can climb like a homesick angel while travelling considerable distances along them. Last year I had the good fortune to soar one that had formed downwind of a volcano in NZ. Probably the most fun you can have sitting down with your clothes on!