Monthly Northern Hemisphere Sea-Level Pressure Grids
X axis: whole world in 72 5.00° steps, first point at 0.00° E, last point at 355.00° E
Y axis: regular grid with 16 5.00° steps, first point at 15.00° N, last point at 90.00° N

Monthly data available from Jan1899 to Mar2019 (1443 months)
Variable slp (observed sealevel pressure) in mb
Full metadata.

Get grid points, average area or generate subset

Mask:	no mask mask1.txt mask5.txt   add a mask to the list
Latitude:	°N - °N
Longitude:	°E - °E
Boundaries:	halfway grid points interpolated
Make:	average max min set of grid points subset of the field
Demand at least:	% valid points in this region

Create a field with lower time resolution

New time scale:	annual (Jul-Jun) annual (Jan-Dec) biannual seasonal
New variable:	mean sd sum sum above sum below number min time of min max time of max first time last time of SLP
Threshold:	no cut less than greater than mb percentile normal 1971-2000
Minimum:	% valid data
First apply:	-month running mean
Missing data:	ignore, climatology, trend, persistence.

Create a field with lower spatial resolution

Average over blocks of longitude and latitude grid cells

Compute geostrophic wind components from this field

Construct a statistical forecast model from this field

Please consider downloading this field from the authoritative site.
If you really want to get it here, Trenberth SLP is available as a netcdf file (size 2.56222 MB).