A spray nozzle for an irrigation sprinkler is provided, wherein the nozzle includes a constriction having a reduced cross sectional flow area achieved using a plurality of channels, the nozzle has a deflector that is configured with depending ribs, each of which has micro-structures that cooperate with other geometry of the rib and deflector to define a plurality of different micro-ramps for dividing the discharged water into different sprays having different characteristics that can be combined to achieve a spray pattern, and/or is arcuately adjustable and includes positive indexing at a plurality of present locations between relatively rotatable components of the nozzle for defining predetermined arcuate extents of the spray pattern.
