LP = Low Pressure; HP = High Pressure
Between the Subtropical Jet (moisture/heat transport into the mid-latitudes) and the Polar Jet (moisture/heat transport poleward), there is another cell circulation of the atmosphere. Not quite as large as the Hadley Cell (shape of the earth+heat/energy loss). Also known as the Mid-Latitude Circulation. Winds at the surface move poleward at the surface and rise as they near the upper latitudes (around 60N/60S), leading to the development of the polar jet. Winds flow equatorward in the upper levels.
As the air from the jet stream diverges from the polar jet, some of that air continues poleward and sinks, forming what tends to be a polar high pressure. Surface winds diverge outward from the high-pressure areas and usually at 60N the winds are predominately easterly.