His answer clearly shows his mastery of the sources as well as his logical halachic approach that makes Judaism--and daily prayer--relevant.
- We make mention (Mazkirim) of HASHEM’s great powers which cause the rain to fall from the evening prayers of last day of Sukoth
- In Erets Yisrael, praying for rain from the 7th of MarHeshwan is no longer relevant since there are no pilgrims who need time to return to their homes outside the Land before the rains begin. We should "mazkir" rain starting from Mossa’e Sh’mini Assereth.
- The Rambam writes that people should pray for rain (Sho’alim) based on the rainy season of that area. This is why the Jews of Bavel differed in their Halakhic practice from their brethren in Erets Yisrael. They waited until the 60th day after the equinox, often erroneously taken to mean, based on the Julian calendar, December 5th, but in fact November 22nd or 23rd. (TY Ta’aniyoth 1:1; TB Ta’anith 10a).
- For the last 1500 years the practice in almost all Galuth communities has been according to the Babylonian custom without regard to their own local conditions--which is a fossilization of Halakha. The Rosh, Tur and Ran spoke out against this and found it strange that Jews living in Western Europe should act as if they resided in Baghdad.
- Jews in Northern Hemisphere countries with climates and seasons similar to Erets Yisrael should act in accordance with the stipulations of the Mishna and Talmudhim. In Northern Hemisphere countries with significantly different weather patterns should adjust when they begin and cease praying for rain.
- Jews in the Southern Hemisphere should pray for rain during their winter.
- Off hand, Rav Bar-Hayim cannot think of any country today with a significant Jewish population with a climate and seasons similar to Bavel.