He used charts of mean 200 - hectopascal circulation for July through August to locate the circumpolar troughs and ridges .
He observed that there is a trough line extending over the eastern and central North Pacific and another one extending over the North Atlantic .
Using charts of mean 200 - hectopascal circulation for July through August to locate the circumpolar troughs and ridges , he observed that there is a trough line extending over the eastern and central North Pacific and another one extending over the North Atlantic .