Well, ASA itself has a limited buffer and looks like we would need external help:
-snmp server
-netflow
-syslog collecter
http://www.cisco.com/en/US/docs/security/asa/asa82/configuration/guide/monitor_syslog.html
the tools used to collect the above info would be able to comile the info and dispay in a user friendly manner and yes, they will be able to save data for longer duration.
Most of these software are paid, you might be luck to get one free with smart features. The likes of kiwi syslog server is available as demo version for 1 month.
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HTH
AJ