The phrase "vertical gradient" refers to the change or difference in something as you move up or down vertically. It indicates how something may vary when going higher or lower. Full definition
There are many factors that can affect the number and intensity of storms — not just the temperature gradient between pole and equator, but also east to west gradients and vertical gradients at both larger and local scales. (sciencemag.org)
That suggests a role for vertical temperature gradients in strengthening winds, such vertical gradients should increase with more global warming. (realclimate.org)
Horizontal temperature gradients are equivalent to vertical gradients in wind velocity, implying implications for the Polar Jet, for example. (tamino.wordpress.com)