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The gravitational intensity at the center of a hemispherical shell of uniform mass density has the direction indicated by the arrow in the above figure.

A hemisphere can be considered to be made up of many infinitesimally thin concentric rings. Figure shows cross-section of a hemisphere of a radius r. It is composed of many rings of radius x where 0<x<r. Gravitational intensity due to a small ring of radius x is $\overrightarrow{dg}$ as shown in the figure. Gravitational intensity due to all rings $=\int dg\hat{j}$. In other words, total gravitational intensity is the integral of gravitational intensity of all infinitesimally small rings which is in the upward direction.