AD Client Global Catalog Availability Monitor. This monitor checks from a client perspective how many Global Catalog Domain Controllers are available. If the number is below the threshold, and alert is raised

Review your AD topology and designate more Global Catalog DCs, or change the minimum number of required GCs for your environment. To change the minimum number of required GCs: Open the Operator Console and navigate to the Authoring section. Expand the "Management Pack Objects" category, then click on "Monitors". Using the "Look for:" box at the top of the window, search for "AD Client Global Catalog Availability Monitor", which should locate a monitor under the Active Directory Client Perspective. Right-click on the monitor, and choose "Overrides", then "Override this monitor", then select the appropriate override type. Enable the override for the "Min. GCs Required Available" parameter, then set and appropriate value. Click OK.