Detective on railway in the tropical season (3)
I believe the answer is:
dry
'tropical season' is the definition.
'dry' can be an answer for 'season' (dry season is a kind of season). I'm not sure about the 'tropical' bit.
'detective on railway' is the wordplay.
'detective' becomes 'd' (this could be a standard abbreviation I've not previously seen).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'railway' becomes 'ry' (abbreviation).
'd'+'ry'='DRY'
'in the' acts as a link.
Can you help me to learn more?
(Other definitions for dry that I've seen before include "Avoiding alcohol" , "Ironic" , "Remove moisture" , "Having given up drinking" , "Thirsty" .)