A second method I have found which greatly reduces the size of compressed gzipped data is to first convert the data to the float16 (half-precision) format and back again to float32. This produces a lot of zeros in the output stream which can shrink file sizes by around 40-60 per cent after compression. One subtlety is that the maximum float16 value is rather low, so you may want to scale your data first, e.g. in python
import numpy as np
import math