The heat wave and floods in various parts of Japan are being caused by an El Nino-like phenomenon in the Central Pacific Ocean, a Japanese researcher said Friday.

Toshio Yamagata, a professor at the University of Tokyo specializing in climate dynamics, said an increase in the sea temperature has activated convection currents and promoted a high-pressure ridge in the Pacific, bringing a hot summer to Japan.

Yamagata said the heat wave might continue until mid-August because of the strong high over the Pacific.

The heat wave has continued to blanket the Tokyo area, with temperatures in the capital rising to record highs near 40, while heavy rain and flooding in Niigata and Fukui prefectures have caused huge damage and loss of life.

El Nino is the name given to a phenomenon in the Pacific off Peru in which the ocean warms up and causes climate abnormalities worldwide.

Yamagata said this year's phenomenon in Japan has not been caused by El Nino, as the water temperature off Peru is colder than average.

However, there is a warm water mass hovering 100 meters below the surface in the Central Pacific around the equator that is causing ocean surface temperatures to be 1 to 1.5 degrees higher than average, he said, calling this a "mock El Nino."

A violent ascending atmospheric current in the Central Pacific is leading to a descending current around Indonesia, causing convection, Yamagata said. The descending air then turns upward around the Philippines, also causing convection there. This accelerates the ascending air, which eventually descends around Japan.

This descending air has created the high-pressure ridge that caused the heat wave and flooding in Japan, he said.