The climate of Australia is significantly influenced by ocean currents, including the Indian Ocean Dipole and the El Niño–Southern Oscillation, which is correlated with periodic drought, and the seasonal tropical low-pressure system that produces cyclones in northern Australia. These factors cause rainfall to vary markedly from year to year. Much of the northern part of the country has a tropical, predominantly summer-rainfall (monsoon). The south-west corner of the country has a Mediterranean climate. The south-east ranges from oceanic (Tasmania and coastal Victoria) to humid subtropical (upper half of New South Wales), with the highlands featuring alpine and subpolar oceanic climates. The interior is arid to semi-arid.