B737 crew has a TCAS RA at 1;200 FT after takeoff from SAN and attempts to comply with the resolution advisory. The target remains co-altitude and ATC advises there is no traffic just before the GPWS advises 'don't sink.' TCAS warnings are then disregarded and cease altogether at 3;000 FT.

Narrative

After lift off from Runway 27 at SAN; we received a TCAS TA followed immediately by a TCAS RA at approximately 1;200 FT MSL. The TCAS command was 'monitor vertical speed' for a climb followed by multiple 'descend; descend' commands. The TCAS displayed target appeared to be immediately off our nose at the same altitude. I disconnected the auto throttles (autopilot was not engaged) and followed the guidance. Both the First Officer and I scanned the area for a visual contact. We did not see any of aircraft. The First Officer queried SAN Tower for traffic; also notifying them of the TCAS RA; and they responded that they didn't see or know of any other traffic. The maximum altitude reached was about 1;600 FT MSL prior to beginning a descent to comply with the RA command. Shortly thereafter; we received multiple GPWS 'don't sink' aural warnings. The minimum altitude reached following the 'descend' RA was about 1;200 MSL. At this point I decided the TCAS RA was a false warning as the target continued to be immediately off our nose at our same altitude and there was no visual/radar/ATC evidence of an actual TCAS aircraft target. With the TCAS RA warning continuing; we resumed a normal climb and continued to clean up following normal procedures (the aircraft was gear up; flaps 5 at the time of the initial TCAS RA). At approximately 3;000 FT MSL the TCAS RA warnings stopped. This entire event happened in day VMC conditions with unlimited visibility and no cloud cover. If this low altitude false TCAS RA event occurred at night or in IMC conditions in an area of rising terrain; it could easily lead to a CFIT type accident if the crew continued to follow the TCAS RA commands.