じゃ意味がない / じゃNounがない

Question

I am quite familiar with Noun じゃない and Na-adj じゃない - in both cases, they negate the noun or na-adjective, and じゃ is a colloquial form of では; ない is the plain form of ありません.

I also know that じゃ conveys the meaning of "well" or "with that" (though that's probably too formal).

せんせいじゃない　・　すきじゃない

じゃ、また。　・　じゃ、はじめましょう。

However, what happens when じゃ is moved in front of the noun or na-adjective? For instance, in the song エアーマンが倒せない (Airman ga Taosenai / I cannot Defeat Airman) the following is heard (0:40):

タイム連{れん}打{だ}も試{ため}してみたけど　竜{たつ}巻{まき}相{あい}手{て}じゃ意{い}味{み}が無{な}い！

I attempted the Time Barrage glitch, but against the tornado it is meaningless!

I would have written 竜巻相手に意味が無い myself.

Could it be that じゃ means に here?

Song: https://www.youtube.com/watch?v=opADNvgeZYY

Lyrics: http://www.animelyrics.com/doujin/nekokan/airman.jis (in kanji, but includes a link to romaji/ english lyrics)

Answer 1

As you said yourself, じゃ is just the colloquial form of では。If the sentence was written more "properly" it would be:

相手では意味が無い

See: では・じゃ

Answer 2

The は particle is frequently when expressing negative things, not just in the case of "ではない" (じゃない) but in a form like form "XはYがない".

While there is some nuance difference, I think for the most part "には意味がない”,"では意味がない”, and "は意味がない” have a similar meaning. You can do a web search and see that they are all used in similar situations.

However, in the specific case of "相手では（じゃ)意味がない”, I feel that there is some sense of the feeling of "with", and the english translation of the example sentence could have been "but with the tornado it is meaningless" (though using "against" is clearly better). Stating just "相手は” seems to me to say something more like "but the tornado is meaningless". This is just my gut feeling, however.

(This is my first post on the board. I'm the author of the blog referred to one of the other answers which is how I found this page. よろしくお願いします (^^) )