Cold and flu season: head congestion, medications which may affect the ears.
To test weather-based theories: compare northern hemisphere and southern hemisphere search trends. (Unfortunately, there's not enough search traffic on [ringing ears] in southern-hemisphere english-speaking regions to be sure... though the thin Australia data is vaguely consistent with the idea their highest traffic is mid-year.)
Whenever I get bad sinus/ear infections during winter my ears ring.The ears/face are very closely related and a simple cold/flu can spark an infection.
To test weather-based theories: compare northern hemisphere and southern hemisphere search trends. (Unfortunately, there's not enough search traffic on [ringing ears] in southern-hemisphere english-speaking regions to be sure... though the thin Australia data is vaguely consistent with the idea their highest traffic is mid-year.)