Jquery Help needed ….

Hi,
I am not that good with JQuery so I am looking for a little help with this solution for an ad banner, this is for a free theme not a commercial venture!

I want to return the screen width with jquery back to a php variable when the page loads.

What I want to do is with a twenty eleven child theme, the theme is responsive but Google ads are not, it looks silly on a mobile if the banner is wider than the screen.

So only once when WordPress opens in a browser if we can get the screen width stored in a variable, then we can load a different adSense banner block based on the screen width.

If the page is opened in a mobile we can display a mobile sized banner.

I have been on google without much luck.

If we have a function something like this, how can we get the returned screen width from a JQuery call to a php variable?

This does not work!

$dr_screen_width = 0;

<script type="text/javascript">
(function($){
	$(document).ready(function () {
		var $dr_screen_width;
		$dr_screen_width = $(window).width();
	});
})(jQuery);
</script>

Any help most welcomed.

Hopefully

David