Ascending sort order for monthly & category view, i.e. ?m=201204, ?cat=4

Question

I have my posts ordered ascending (from oldest to newest) because I use Wordpress as a website to accompany a book published based on the original blog. To do this I put the following code just before The Loop in index.php of my custom version of the Connections theme:

<?php
    $wp_query->set('orderby', 'post_date');
    $wp_query->set('order', 'ASC');
    $wp_query->get_posts();
?>

This works fine for the main index and for when the posts are displayed by page, i.e.:
index.php?paged=1

However, when the posts are retrieved by month or by category, the sort order defaults to DESC, i.e.: http://www.justanothersoldier.com/?cat=4

http://www.justanothersoldier.com/?m=200312

I just want everything to always be ASC. Are there monthly and category templates I need to edit? Thanks.