In the context of the IAP 2-level AGCM, numerical study was performed of effects on summer Northern atmospheric low-frequency circulations of two kinds of heat source forcing (constant and quasi-biweekly) in the mid-upper troposphere. Evidence suggests that either of the sources is responsible for a particular teleconnection pattern associated with a characteristic system; the constant source excites a low-frequency wavetrain analogous to PNA pattern associated with 1972 ENSO at a development phase and the related low-frequency cyclone and anticyclone are produced in the tropical NW Pacific, travelling along the wavetrain and disappearing in SE North America; the quasi-biweekly one generates a very strong teleconnection, showing meridional wavenumber 1 over the tropical NW Pacificmidlatitude Asia; the low-frequency system forms in the Northern Hemisphere, moving northward at 1 degree per day and reaching its maximum strength at subtropics.