The doldrums are a belt of persistently light, unpredictable winds that encircles the globe near the equator, roughly where the trade winds from the Northern and Southern Hemispheres meet and cancel each other out. Sailors have dreaded the zone for centuries because a ship under sail could sit motionless for days or weeks, baking under equatorial sun. The region overlaps with what meteorologists call the Intertropical Convergence Zone, but recent research shows the relationship between the two is more nuanced than textbooks have suggested, with calms and storms coexisting in ways that are only now being properly modeled.
Where the Wind Dies and Why
The doldrums sit between the northeast trade winds of the Northern Hemisphere and the southeast trade winds of the Southern Hemisphere. As those wind systems converge near the equator, the horizontal push that drives surface air slows dramatically. The heated equatorial surface also causes air to rise, creating a low-pressure trough at the surface. With little pressure difference to drive horizontal flow, the wind can drop to nearly nothing.
The band is not fixed in one place. It migrates north and south with the seasons, following the sun’s position. During Northern Hemisphere summer it drifts north, sometimes reaching 10° to 15° north latitude over parts of Africa and Asia. In winter it retreats south. Over the open Atlantic and Pacific, it tends to hover a few degrees north of the equator year-round, partly because the distribution of land and ocean in the Northern Hemisphere keeps it slightly off-center.
Countries that sit squarely in this zone deal with its effects every day. Malaysia, positioned about 5° north of the equator, experiences average wind speeds that swing from around 8 meters per second during the monsoon season down to a gentle breeze of roughly 3 meters per second between monsoons.1Renewable Energy. Feasibility assessment of wind energy resources in Malaysia based on NWP models That kind of variability is characteristic of life inside the doldrums belt.p>
Calm Winds and Heavy Rain Are Not Opposites Here
One of the more counterintuitive things about the doldrums is that this zone of feeble surface winds is also one of the rainiest places on Earth. The rising air that robs the surface of wind climbs thousands of meters, cools, and dumps enormous quantities of moisture. Towering cumulonimbus clouds, squalls, and sudden thunderstorms are routine. A ship might sit becalmed for hours, then get hammered by a violent downpour with gusting winds before the air goes still again.
A 2024 study using both reanalysis data and ocean buoy measurements found that the doldrums are largely confined between the edges of the Intertropical Convergence Zone marked by enhanced surface convergence, and the region between those edges is indeed one of high average rainfall. But the actual low-wind-speed events tend to happen when and where it is not raining. The researchers hypothesized that the calm spells occur specifically in pockets of low-level divergence rather than convergence.2Geophysical Research Letters. The Calm and Variable Inner Life of the Atlantic Intertropical Convergence Zone: The Relationship Between the Doldrums and Surface Convergence In other words, within the broader rainy belt, there are sub-regions where air is spreading apart at low levels instead of piling together, and those pockets are where the wind really vanishes.
This finding matters because for a long time climate models had trouble reproducing the doldrums at all. Storm-resolving simulations over the tropical Atlantic, run at fine enough resolution to capture individual thunderstorm systems, found that the doldrums emerged as one of the most prominent features of the wind field. When the same simulations were run at coarser resolution with convection handled by approximation rather than direct calculation, the doldrums became far less pronounced.3Nature Geoscience. Rediscovery of the doldrums in storm-resolving simulations over the tropical Atlantic The coupling between individual storm-scale dynamics and surface winds seems to be essential for maintaining the calm zones. Without modeling individual storms, the models smooth out the very feature that makes the doldrums the doldrums.
How El Niño Reshuffles the Belt
Because the doldrums track the Intertropical Convergence Zone, anything that shifts the ITCZ shifts the doldrums with it. El Niño and La Niña are the most powerful short-term drivers. During El Niño, when the central and eastern tropical Pacific warms abnormally, the convergence zone over Africa shifts northward while the South American convergence zone shifts southward. La Niña reverses the pattern: the African ITCZ moves south and the South American ITCZ moves north.4Environmental Development. Response of the global ITCZ to ENSO and how the ITCZ determined from maximum precipitation compares with the surface tropical wind convergence These shifts are not uniform around the globe. They vary by ocean basin and by season, meaning the doldrums can widen in one part of the tropics while narrowing in another during the same El Niño event.
There is even a distinction between different flavors of El Niño. During the conventional eastern Pacific type, the convergence zone can shift southward extensively. But during a central Pacific El Niño, one study found the eastern Pacific ITCZ barely moves, shifting only slightly southward in peak season and showing little anomalous movement the rest of the year.5Geophysical Research Letters. Revisiting the latitude fluctuations of the eastern Pacific ITCZ during the central Pacific El Niño For sailors or shipping planners trying to predict where the lightest winds will be in a given year, the type of El Niño matters as much as whether one is happening at all.
What Happens to the Ocean Underneath
The calm winds that define the doldrums have a direct effect on the sea surface. Normally, wind stirs the upper ocean and mixes cooler water from below with the sun-warmed surface layer. When the wind stops, that mixing slows dramatically, and the top few meters of the ocean can heat up fast. Research on global diurnal sea surface temperature variability has shown that the most extreme daytime warming events in the tropics occur under exactly these conditions: calm winds, clear skies, and little to no rain.6Journal of Geophysical Research: Oceans. Global Diurnal Sea Surface Temperature Variability and the Role of Ocean‐Atmosphere Interactions A patch of ocean in the doldrums on a cloudless, windless afternoon can become noticeably warmer than the surrounding water, creating a thin warm skin at the surface.
On larger scales, the ocean currents that flow beneath the doldrums are tightly linked to the convergence zone above them. The North Equatorial Countercurrent, an eastward-flowing current in the tropical Pacific, interacts with the ITCZ through a positive feedback loop. A stronger countercurrent carries warm water from the western Pacific eastward, raising sea surface temperatures along its path, which intensifies the convection within the ITCZ and strengthens the wind patterns that in turn drive the countercurrent harder.7PubMed Central. Coupled dynamics of the North Equatorial Countercurrent and Intertropical Convergence Zone with relevance to the double-ITCZ problem If that current weakens, the ITCZ weakens too, and a secondary convergence zone south of the equator can strengthen in its place. This kind of ocean-atmosphere coupling helps explain why the doldrums are not simply a byproduct of wind patterns but are part of a larger system where ocean heat and atmospheric circulation reinforce each other.
Why Hurricanes Almost Never Form in the Doldrums
Given the warm water and towering thunderstorms, you might expect tropical cyclones to spin up easily in the doldrums. They almost never do, and the reason is straightforward: the Coriolis effect near the equator is essentially zero. Without that deflecting force, air rushing toward a low-pressure center does not curve into the spiral pattern that sustains a tropical cyclone. Storms that do develop within about 5° of the equator are exceptionally rare.
Idealized model experiments have tested what happens when an already-formed tropical cyclone is moved to near-equatorial conditions. The storm weakens, but depending on its initial intensity, it can take several days to decay to tropical storm strength. The weakening happens because reduced Coriolis force destabilizes the storm’s internal structure: both inflow and outflow strengthen throughout the storm’s depth, downdrafts intensify in the outer rainbands, and dry mid-level air gets entrained into the boundary layer, suppressing the deep convection the storm needs to survive.8Quarterly Journal of the Royal Meteorological Society. Can tropical cyclones exist near the Equator?
That said, “almost never” is not “never.” There are documented cases of vortex formation right at the equator, typically within a broader region of counterclockwise flow that already contains positive vertical vorticity extending several degrees south of the equator. Deep convection stretches and concentrates patches of that vorticity, and the collective effect of many convective cells fluxes vorticity inward at low levels, gradually spinning up a vortex. The process turns out to be fundamentally the same one that spins up cyclones farther from the equator; it just needs a preexisting supply of rotation in the surrounding atmosphere.9Quarterly Journal of the Royal Meteorological Society. Tropical cyclogenesis at and near the Equator These events are meteorological curiosities, but they demonstrate that the doldrums are not as meteorologically inert as their reputation suggests.
An Atmospheric Washing Machine
The vigorous convection in the doldrums does something that rarely gets mentioned outside atmospheric chemistry circles: it scrubs the air. Aerosols, including pollution, dust, and sea salt particles, get swept upward by the towering convective cells and washed out by rain. Research during the Indian Ocean Experiment found that aerosol concentrations south of the ITCZ were dramatically lower than concentrations north of it, because the convective activity, mixing, and wet removal within the convergence zone depleted them. In intense convection with precipitation, the lifetime of aerosols in the boundary layer was on the order of hours, while on average across the study period it ranged from one to three days.10Journal of Geophysical Research: Atmospheres. A study of the impact of the Intertropical Convergence Zone on aerosols during INDOEX
This means the doldrums act as a kind of atmospheric barrier. Pollution generated in the Northern Hemisphere, particularly from industrial regions of South and Southeast Asia, gets partially cleaned before it crosses into the Southern Hemisphere. The barrier is not perfect, especially when the ITCZ is weak or when aerosols are lofted high enough to travel above the rain, but it is effective enough that air-quality measurements on either side of the convergence zone can look like they come from different planets.
How Climate Change May Reshape the Doldrums
Climate scientists have been working to figure out whether the doldrums will move, widen, narrow, or intensify as the planet warms. The picture is still being sorted out, and some of the findings seem contradictory at first glance.
Satellite observations and reanalysis data over recent decades show a narrowing and strengthening of precipitation in the ITCZ over both the Atlantic and Pacific, with little change in its overall position.11PubMed Central. Response of the Intertropical Convergence Zone to Climate Change: Location, Width, and Strength Coupled climate models agree that there is no robust shift in the zonal-mean ITCZ position projected for the coming century. But the details under that top-line finding are more complex. The majority of models project continued narrowing of the ITCZ and a weakening of the mean upward air motion within it, with an interesting twist: changes in width and strength tend to be strongly anti-correlated across models, meaning models that predict more narrowing also tend to predict less weakening, and vice versa.
Under future warming scenarios, seasonal convergence zones are projected to shift equatorward, widen, and weaken.12Geophysical Research Letters. Contrasting Recent and Future ITCZ Changes From Distinct Tropical Warming Patterns That equatorward shift of the seasonal extremes, even while the annual mean stays roughly put, would squeeze the annual-mean tropical ascent zone into a narrower latitude range. For the doldrums, that could mean calmer conditions concentrated in a tighter band rather than spread across a wide swath of ocean.
The picture gets even more complicated when you look region by region. Projections from 27 state-of-the-art climate models show a zonally varying response by 2100: the ITCZ shifts northward over eastern Africa and the Indian Ocean, but southward over the eastern Pacific and Atlantic.13PubMed Central. Zonally contrasting shifts of the tropical rainbelt in response to climate change The doldrums would not simply move north or south as a unit; they would tilt, bulging northward in some ocean basins and southward in others. That has real implications for shipping routes, fisheries, and rainfall in equatorial nations.
For context on how stable the ITCZ has been over deeper time, modeling of past climates suggests that even during dramatic shifts like the Last Glacial Maximum and Heinrich Stadial 1, the mean position of the ITCZ shifted by less than 1° of latitude.14Earth and Planetary Science Letters. Changes in ITCZ location and cross-equatorial heat transport at the Last Glacial Maximum, Heinrich Stadial 1, and the mid-Holocene The system is anchored near the equator by powerful energy-balance constraints, and it takes a lot to move it far.
Wind Energy in the Doldrums Belt
The low wind speeds that defined the doldrums as a navigational nightmare create a different kind of challenge in the age of renewable energy. Countries near the equator often have abundant solar resources but struggle with wind power because average wind speeds are so modest. Malaysia’s experience is instructive. Sitting squarely in the doldrums belt, the country has long been written off as unsuitable for wind energy. But a detailed assessment using numerical weather prediction models found that mesoscale wind patterns, driven by local topography and land-sea contrasts, create viable wind resources in some locations even within the overall low-wind zone. The study identified several economically viable wind turbine sites, contradicting the assumption that equatorial countries cannot harness wind power at all.15Renewable Energy. Feasibility assessment of wind energy resources in Malaysia based on NWP models
The key insight is that “doldrums” describes a large-scale average, and averages hide a lot of local variation. Coastal areas with strong sea-breeze effects, mountain gaps that funnel air, and monsoon transitions all create windows of usable wind even in the calmest part of the tropics. Wind energy developers in equatorial regions have to think in terms of mesoscale meteorology rather than broad climate zones. The same logic applies to modern sailing and shipping: routing algorithms now incorporate fine-scale wind forecasts to thread through the doldrums rather than simply waiting for the wind to return, as sailors of earlier centuries had no choice but to do.
Monitoring the Doldrums from Space
Measuring wind over remote stretches of open ocean used to require ships, buoys, or the occasional research aircraft. Today, satellite-based scatterometers do most of the heavy lifting. Instruments like the SeaWinds radar aboard NASA’s QuikSCAT satellite work by bouncing microwave pulses off the sea surface and measuring the backscatter. Wind generates ripples and small waves that roughen the water; the rougher the surface, the stronger the return signal. By analyzing how the backscattered power varies with direction, the instrument can calculate both wind speed and wind direction across the ocean surface.16PLoS ONE. Ocean Surface Winds Drive Dynamics of Transoceanic Aerial Movements
This technology has been transformative for understanding the doldrums because the zone is so remote and so variable from day to day. Buoy networks are sparse in the deep tropics, and ship traffic avoids the calmest areas when it can. Satellite passes provide near-global coverage every day or two, making it possible to track the edges of the doldrums as they shift with the seasons, respond to El Niño, and fluctuate on weekly timescales. That data feeds into the reanalysis products and storm-resolving models that have finally allowed scientists to see the doldrums clearly in their simulations, closing a gap that had persisted for decades in our understanding of one of the most distinctive and consequential wind features on the planet.