How faraway Atlantic waters influence Asia’s summer rainfall

The northern edge of the Tibetan Plateau looks dry at first glance, but summer rainfall keep the Tarim Basin alive. Farmers, cities, and fragile oases depend on that short wet season to refill rivers and soil.

A new study reports that a North Atlantic sea surface temperature dipole helps steer those rains.

Year-to-year changes in summer precipitation explain 77 percent of the total variability across the region. The finding connects a faraway ocean to local water budgets with a clear physical chain.

Ocean patterns drive summer rainfall

The work was led by Shijie Tang of the Institute of Atmospheric Physics, Chinese Academy of Sciences.

The team focused on the Kunlun Mountains, which rise for about 1,550 miles across Central Asia and form the plateau’s northern wall.

Scientists use the word “teleconnection” to describe climate links between far-apart places that move energy and momentum through the atmosphere.

In this case, the North Atlantic’s temperature pattern sends ripples through the upper atmosphere that arrive over Eurasia and shift wind and rain.

Ocean temperatures move winds

The key messenger is a train of Rossby waves. These are large, meandering disturbances in the jet stream that can travel long distances and alter pressure and wind.

Wave energy propagation has a standard diagnostic – the wave activity flux – which has been formulated for practical use.

In summers when the North Atlantic shows a dipole, with warmer waters south of Greenland and cooler waters off the U.S. East Coast, those waves tend to march east from Western Europe into northern Central Asia.

The pattern favors an anticyclonic circulation east of the Caspian and anomalous southerly flow near the Kunlun crest.

Ocean heat meets atmosphere

The authors filtered multiple observation and reanalysis datasets to isolate year-to-year signals from 1980 to 2021. They then diagnosed moisture budgets to separate thermodynamic effects from dynamic ones.

Their analysis points to meridional wind anomalies as the main lever on rainfall. Southerly flow brings extra water vapor toward the mountains. Horizontal vapor convergence emerges as the leading term in the budget.

“This research provides a new framework for understanding rainfall variability by connecting remote ocean atmosphere interactions to local water processes,” said Tianjun Zhou, the corresponding author from CAS.

The team argues that this linkage can help inform climate risk planning in a region where a missed summer can ripple downstream for months.

North Atlantic shapes summers

Surface heat fluxes over the North Atlantic help create pressure anomalies in the troposphere.

This is the lowest layer of the atmosphere where weather happens. Those anomalies launch the wave train that arcs into Eurasia along the subtropical jet.

“On the northern slope of the Tibetan Plateau, annual rainfall is dominated by summer precipitation, with interannual variability accounting for most of the changes,” said Tang.

That emphasis on summer lines up with what communities on the ground already experience.

Independent work has shown that the North Atlantic tripole can modulate summer rainfall across Eurasia – not just in China. It does so by exciting similar wave trains and shifting storm tracks, especially in mid- to high latitudes.

The present study places the Kunlun and northern Tibetan Plateau into that broader picture with local detail.

Oscillation alters Tibetan storms

Many readers may know of the North Atlantic Oscillation (NAO) from winter forecasts, but a summer NAO pattern also matters for East and Central Asian rainfall.

Prior work found that the summer NAO can influence Tibetan Plateau precipitation through wave trains and changes to the westerlies.

That link is not constant through time. Studies have reported periods when the connection between the summer NAO and Tibetan precipitation weakens or flips sign.

Ocean temperatures impact lives

When a faraway ocean helps nudge winds over the plateau, the change is not academic.

Reservoir managers, farmers, and hazard planners in the Tarim Basin feel the outcome in river flow, irrigation demand, and flash-flood risk.

Better anticipation of a wet or dry summer can guide water releases and emergency readiness.

That is the practical value of tracing a teleconnection from the ocean to the mountains with a clear mechanism rather than a loose correlation.

What makes this approach credible

The authors tested their diagnosis with multiple observational datasets and added support from climate model ensembles. They found consistent signatures in the upper level wind fields and moisture convergence terms.

They also showed that the circulation pattern over the Kunlun ties back to the North Atlantic dipole. The connection follows a specific path that runs from Western Europe into northern Central Asia.

That pathway helps differentiate this mechanism from others, such as signals tied to tropical Pacific variability, which tend to favor different sectors of the plateau.

Climate patterns need testing

Two questions sit on the horizon. First, how predictable is the North Atlantic dipole one to two seasons ahead, and does that lead time translate into actionable forecast skill over the Kunlun?

Second, how will ongoing ocean temperatures and warming patterns shape the frequency or intensity of the dipole and its wave trains?

Answers will require careful model evaluation against observations and a tight focus on how moisture transport responds, not just how rainfall totals change.

The study is published in Climate Dynamics.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–