Relationship between the geomagnetic Dst(min) and the interplanetary Bz(min) during cycle 23

In cycle 23 for geomagnetic storms of −Dst(min) >50 nT, the plot of −Dst(min) versus −Bz(min) for the low −Bz(min) range 0–10 nT showed erratic variation in Dst(min), (correlation 0.19). Even for −Bz(min) range 10–20 nT, −Dst(min) values had considerable scatter (correlation 0.57). For −Bz(min).>20 nT, the relationship was good (correlation 0.82). For the whole range −Bz(min) 0–50 nT, the correlation was high (0.88). Thus, if −Bz(min) is very large (∼20 nT), large −Dst(min) occurs but in a wide range of 100–500 nT.