9526890 Constable Lava flows, marine sediments and magnetic anomaly data will be used to model the long term structure and variability in the geomagnetic field. Data from both lava flows and sediments indicated different average field configurations during normal and reverse polarity periods for the past 5Ma, although the individual models based on each type of data are poorly constrained. The PI's propose to investigate how long a time interval is required to sample the full range of secular variation to get a good average of the geomagnetic field. The PI's will also use paleointensity data to derive new paleosecular variation models. Existing paleointensity data are incompatible with the current model of Constable & Parker, that is isotopic in variability with respect to any geocentric coordinate system. New models will sought, using evolutionary programming, that allow for anisotropy along the geographic axis. Very long-term (millions of years) non-zonal structure in the geomagnetic field, that may reflect control by core-mantle boundary conditions will be investigated by looking for anomalies in the time-averaged field and the paleosecular variation that correspond to similar structures seen in the historical field.
