Intertropical Convergence Zone Research Articles

Deciphering the Characteristics and Drivers of the Summer Monsoon Precipitation Extremes Over the Indian Himalayas

AbstractThis study investigates the physical processes behind extreme precipitation events (EPEs) in the Himalayas, notorious for causing frequent floods and significant loss of life and property. Due to the presence of complex terrain, understanding the driving factors of these EPEs is challenging. Here, we decipher the precipitation characteristics and their driving factors responsible for the occurrence of EPEs in the Western Himalayas (WH) for the period 1979–2020. EPEs are defined as events exceeding the 99th percentile threshold. The extreme precipitation in the WH is contributed by both large‐scale precipitation (accounting for 61%) and convective precipitation (39%). Moreover, 25.49% of EPEs in this region are directly associated with monsoon depressions. The presence of distinct upper‐tropospheric gyres flanking the WH, along with a prominent zonal wave pattern, promotes a southward extension of the trough. This intensifies the low‐level convergence of moisture‐laden winds from the adjoining seas, resulting in substantial moisture availability for the EPEs. An omega‐type blocking pattern emerges 4 days before EPEs, facilitating the intrusion of an extratropical cyclonic circulation. This circulation, characterized by its slow eastward and equatorward movement, leads to low‐level moisture flux convergence and ascending motions, which in turn trigger the EPEs. This highlights the crucial role of extratropical signals in driving EPEs and implies that tropical‐extratropical interactions play an important role in these EPEs. Furthermore, the shifting of the Intertropical Convergence Zone is strongly linked to the enhancement of the intensity of EPEs. Moreover, moisture budget analysis shows that EPEs over the WH are primarily driven by vertical advection, with the dynamic (thermodynamic) terms explaining 92% (8%) contribution. The intensified diabatic heating structure further enhances the convection, facilitating the development of deep convection which controls the local thermodynamics of these EREs. Lastly, our study demonstrated that most intensified and persistent EPEs over the Himalayas are found to be linked with Quasi‐Resonance Amplification, which is driven by baroclinic waves with 5 and 8 zonal wave numbers that contribute to these EPEs.

Community structure of tropics emerging from spatio-temporal variations in the Intertropical Convergence Zone dynamics

The Intertropical Convergence Zone (ITCZ) is a narrow tropical belt of deep convective clouds, intense precipitation, and monsoon circulations encircling the Earth. Complex interactions between the ITCZ and local geophysical dynamics result in high climate variability, making weather forecasting and prediction of extreme rainfall or drought events challenging. We unravel the complex spatio-temporal dynamics of the ITCZ and the resulting teleconnection patterns via a novel tropical climate classification achieved using complex network analysis and community detection. We reduce the high-dimensional complex ITCZ dynamics into a simple yet insightful community structure that classifies the tropics into seven regions representing distinct ITCZ dynamics. The two largest communities, encompassing landmasses over the Northern and Southern hemispheres, are associated with coherent seasonal ITCZ dynamics and have significant long-range connections. Temporal analysis of the community structure highlights that the tropical Pacific and Atlantic Oceans communities exhibit substantial variation on multidecadal scales. Further, these communities exhibit incoherent dynamics due to atmosphere-ocean interactions driven by equatorial and coastal oceanic upwelling.

Understanding the Zonal Variability in Projections of Sahel Precipitation

AbstractThe uncertainty in precipitation projections across the Sahel has persisted across generations of climate models. Many projections show a zonal dipole in the sign of precipitation change, with wetting across the Central Sahel and drying across the Western Sahel. We analyze the outputs from an ensemble of current climate models to explain why some produce this dipole and understand the inter‐model variability in the transition region for these models. Models projecting the dipole tend to shift the Atlantic Intertropical Convergence Zone (ITCZ) to the south, while models that do not tend to shift the ITCZ to the north. We find that the strong relationship between the change in Sahel precipitation and surface temperature‐based indices is highly driven by the non‐dipole models. These indices do not explain most of the variance in where models transition. This suggests that understanding zonal variability in Sahel precipitation change must go beyond these temperature‐based analysis.

Precipitation variability and environmental change across late Quaternary glacial-interglacial cycles in lowland Central America: Insights from Lake Petén Itzá (Guatemala) sediments

Lowland Central America, a biodiversity hotspot in the northern Neotropics, is a region where the climate is influenced by the location and expansion-contraction of the Intertropical Convergence Zone (ITCZ) on seasonal to millennial timescales. Paleo-records from the Caribbean Sea and the eastern equatorial and subtropical Pacific Ocean illustrate the response of regional precipitation to fluctuations in global temperature, driven by glacial-interglacial cyclicity over the past 500 kyr. Here, we present a paleoclimate and paleoenvironment record from Lake Petén Itzá, lowland Guatemala, which spans the last ∼413 kyr. Sediment in the lake recorded lacustrine and terrestrial ecosystem responses to large-scale climate variability. Precipitation patterns during MIS11-9 (∼413-304 ka BP) align with the latitudinal position of the ITCZ, with superimposed effects from the strength of the Caribbean Low-Level Jet (CLLJ). A sediment hiatus, likely attributable to mass removal processes in the lake's shallower areas, spans the period from MIS8 (starting at 304 ka BP) to the end of MIS6 (at 149 ka BP). MIS6 was characterized by humid conditions, perhaps ascribable to a more southerly extension of cold fronts and intensification of the CLLJ. During MIS5, pronounced fluctuations among all sediment variables, accompanied by an abrupt decline in precipitation, may correspond with cold events inferred from North Atlantic Ocean sediment cores. Although discontinuous, the Lake Petén Itzá sediment record provides a window into late Quaternary climate and environmental change in lowland Central America.

Imprints of Atlantic Multidecadal Oscillation on pantropical seawater pH inferred from coral δ11B records

Understanding natural variability in seawater pH (pHsw) is crucial for predicting future ocean acidification. Coral boron isotopes (δ11B) offer an alternative method to extend pHsw records back centuries, shedding light on how pHsw varies over time. This study compiles both new and existing coral δ11B records from pantropical oceans to investigate multidecadal pHsw variability and its connection to climate variability. A notable finding is the pronounced influence of the Atlantic Multidecadal Oscillation (AMO) on pantropical coral δ11B-pH variations. This is primarily interpreted as the effects of AMO-associated climate changes on reef pHsw, rather than influencing coral physiological processes related to calcifying fluid pH. Key factors like wind speeds and hydrological variability related to Intertropical Convergence Zone (ITCZ) shifts are identified as potential drivers of the AMO's impact on pHsw. This study thus provides valuable insights into the broader effects of the Atlantic climate on pantropical seawater CO2 system.

Tracking orbital and suborbital climate variability in the westernmost Mediterranean over the past 13,000 years: New insights from paleoperspectives on marine productivity responses

This study presents a comprehensive analysis of a sediment record from the Western Alboran Basin (core GP04PC), utilizing palynological and geochemical tools to investigate marine productivity responses to orbital and suborbital climate variability over the past 13,000 years. High productivity during the Younger Dryas humid phase (∼12.4–11.7 ka) and the Holocene humidity optimum (∼10.5–8.5 ka) was driven by increased local river discharges resulting from rapid mountain glaciers melting and enhanced regional precipitation. During the late Holocene, frequent flood events linked to negative North Atlantic Oscillation (NAO) incursions potentially led to multicentennial-scale productivity increases. The findings indicate that periods characterized by wet regional conditions and increased river run-off, influenced by orbital (e.g., insolation cycles) and suborbital factors (e.g., NAO and Atlantic Meridional Overturning Circulation changes), consistently enhanced marine productivity in the Western Alboran Basin. The study also reveals that the current high productivity and carbon export in the Western Alboran Basin are maintained by active upwelling and downwelling systems driven by a persistent positive NAO phase following the southward migration of the Intertropical Convergence Zone (ITCZ) that occurred around 6.5 ka. Furthermore, geochemical proxies support a strong detrital influence on trace metal concentrations, including barium (Ba), in deep Western Alboran sediments during the Holocene. This limits the use of Ba/Al ratios for accurately reconstructing productivity changes and highlights the importance of dinocyst analysis as a complementary tool for robust marine productivity reconstructions in this region. These observations provide valuable paleoperspectives on marine ecosystem responses to climate variability, contributing to the development of robust long-term productivity models essential for adapting to ongoing environmental changes in the region, and demonstrating the strong influence of North Atlantic climate and ocean dynamics on centennial-scale productivity oscillations in this region.

A slower North Equatorial Countercurrent but faster Equatorial Undercurrent in a warming climate

Abstract We analyze century-end projections for the tropical Pacific upper-ocean currents simulated within the Climate Model Intercomparison Project Phase 6 (CMIP6) under global warming. We find that while the intensity of precipitation within the Intertropical Convergence Zone (ITCZ) increases, the ITCZ also shifts towards the equator and broadens, which reduces wind stress curl north of the equator. Consequently, the North Equatorial Countercurrent (NECC) shifts equatorward, following the ITCZ, and weakens, despite the more intense ITCZ. The strength of the North Equatorial Current (NEC) and the South Equatorial Current (SEC) also decreases due to the weakening of the Walker circulation and the corresponding wind stress. However, despite the weaker winds, the Equatorial Undercurrent (EUC) intensifies as it shoals due to stronger vertical stratification induced by surface warming. Furthermore, we find a slightly stronger zonal pressure gradient along the core of the EUC, instead of a weaker one expected from weaker wind stress and sea surface height gradient along the equator. Ultimately, we argue that it is reduced vertical friction theory due to increased ocean stratification and hence larger Richardson number that explains the faster EUC. These intricate balances control future changes in equatorial currents, and the uncertainties of projected changes need to be further examined.

Late Pleistocene to early Holocene vegetation and environmental changes in the tropical Leizhou Peninsula, South China: New evidence from the n-alkane record

Understanding past long-term vegetation responses to regional or even global climate change and forcing mechanisms is essential to future climate change projections. However, due to the lack of long-term terrestrial sedimentary records, there are few studies focusing on vegetation changes in tropical southern China since the last glacial period, especially from the perspective of peat n-alkane records. Here, we have presented a peat core record from the Xialu peatland in the northern Leizhou Peninsula, and n-alkanes were investigated in conjunction with multiple proxy indicators. Our results showed that the organic matter sources were mainly a mixture of aquatic and terrestrial vegetation, with terrestrial vegetation accounting for most of the bulk organic matter composition. From ∼44.1 to 29 cal kyr BP, the organic matter source was mainly dominated by terrestrial vegetation, which corresponds to warm and humid conditions. From 29 to 14 cal kyr BP, the input of the terrestrial vegetation was reduced, the aquatic vegetation input increased, implying cool and dry conditions. From 14 to 9.3 cal kyr BP, the climate gradually became warmer and wetter, and terrestrial vegetation dominated in this area. Overall, the climatic conditions from the Xialu peatland were generally consistent with other records from adjacent areas. Our results suggest that, during the Last Glacial Maximum (LGM), a substantial drop in regional and global sea levels may have been the main cause of drought in tropical southern China on orbital timescales. Meanwhile, several climatic fluctuations on millennial timescales could have been influenced by the variability of the North Atlantic Meridional Overturning Circulation (AMOC) and migration of the Intertropical Convergence Zone (ITCZ).

Climatological Tracking and Lifecycle Characteristics of Mesoscale Convective Systems in Northwestern South America

AbstractMesoscale convective systems (MCSs) are crucial in shaping large‐scale tropical circulation and the hydrological cycle, particularly in Northwestern South America (NwSA), a region marked by complex terrain and significant MCS activity. Understanding MCSs in NwSA is vital due to their impact on precipitation patterns and potential for severe weather events. To enhance this understanding, the ATRACKCS algorithm was developed for tracking convective systems, utilizing precipitation and brightness temperature data sets. This research focuses on documenting the spatiotemporal variability of MCS occurrence, life cycle, and movement. Notably, MCS hotspots were identified to the west of the major orographic features in the region, with maximum occurrences at night, contrasting with the region's typical afternoon peak in land convection. MCS movement is also heavily influenced by topography, with higher velocities on the eastern (windward) side of the Andes compared to velocities on the western (leeward) side. MCSs generally move westward, driven by easterly winds, but this pattern is not consistent throughout the year or region. Northward movement is predominant to the west of the Andes, while southward movement is observed to the east. These seasonal and regional movement variations are linked to factors such as the intertropical convergence zone position, moisture availability, topography, and low‐level jets. This research underscores the complexity of MCSs in NwSA and emphasizes the need for detailed studies on the atmospheric environment shaping these systems. Additionally, it provides a robust 21‐year MCS database for NwSA and an advanced tracking tool for research in various geographic contexts and impact areas.

Detection of Dominant Rainfall Patterns in Indonesian Regions Using Empirical Orthogonal Function (EOF) and Its Relation with ENSO and IOD Events

Several studies indicate that Indonesia’s position on the equator, where winds from the northern and southern hemispheres converge, leads to year-round rainfall in Indonesia. Previous studies have also shown the presence of monsoon winds over Indonesia, which causes rain in Indonesia to follow the Asian and Australian monsoon wind patterns. Recently, variations in rainfall patterns and intensity in Indonesia have been highly volatile and difficult to predict. This study uses gridded data analysis of ocean-atmospheric rainfall for 69 years (1948–2016) to detect monsoonal, equatorial, and local signals and relate them to ENSO and IOD events. Rainfall analysis reveals that the first mode accounts for 38.57%, the second 13.92%, and the third 8.93% of the total variance. These results show that these variants are very variable, both in space and time. Monsoonal patterns were detected in the southern region of Indonesia, equatorial patterns in northern Sumatra and western Kalimantan, while local patterns were detected in Maluku and the Maluku Islands. Furthermore, the monsoonal and local rainfall patterns are strongly correlated (> 0.85) with local SST, but the equatorial rainfall pattern is weakly correlated (< 0.5) with local SST. Note that the equatorial pattern is associated with the Inter Tropical Convergence Zone (ITCZ) phase. The varied vector correlation map illustrates the asymmetric fluctuations in sea surface temperature and the simultaneous existence of winds coming from the west from the Indian Ocean and winds coming from the east from the Pacific Ocean during the period of heavy precipitation.

Enhanced “Wind‐Evaporation Effect” Drove the “Deep‐Tropical Contraction” in the Early Eocene

AbstractThe equatorward contraction of tropical precipitation, commonly referred to as the “deep‐tropical contraction”, is witnessed in the paleoclimate simulations of the early Eocene. However, the mechanism driving this contraction is still unclear. Based on the energetics framework of the Intertropical Convergence Zone (ITCZ) and the decomposition method of the latent heat flux along with the simulations of a climate system model, CESM1.2, we proposed a novel mechanism responsible for the “deep‐tropical contraction” in the early Eocene. The greenhouse gases‐induced sea surface warming amplifies the sensitivity of evaporation to surface wind speed changes through Clausius‐Clapeyron scaling, leading to an interhemispheric asymmetric enhancement of the latent heat flux. To maintain hemispheric energy balance, the cross‐equatorial atmospheric energy transport must be reduced during the solstice seasons. As a result, the solstitial location of the ITCZ shifts equatorward, causing the “deep‐tropical contraction” in the early Eocene.

Light-absorbing black carbon and brown carbon components of smoke aerosol from DSCOVR EPIC measurements over North America and central Africa

Abstract. Wildfires and agricultural burning generate seemingly increasing smoke aerosol emissions, impacting societal and natural ecosystems. To understand smoke's effects on climate and public health, we analyzed the spatiotemporal distribution of smoke aerosols, focusing on two major light-absorbing components, namely black carbon (BC) and brown carbon (BrC) aerosols. Using NASA's Earth Polychromatic Imaging Camera (EPIC) instrument aboard NOAA's Deep Space Climate Observatory (DSCOVR) spacecraft, we inferred BC and BrC volume fractions and particle mass concentrations based on spectral absorption provided by the Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm with 1–2 h temporal resolution and ∼ 10 km spatial resolution over North America and central Africa. Our analyses of regional smoke properties reveal distinct characteristics for aerosol optical depth (AOD) at 443 nm, spectral single-scattering albedo (SSA), aerosol layer height (ALH), and BC and BrC amounts. Smoke aerosols in North America showed extremely high AOD up to 6, with elevated ALH (6–7 km) and significant BrC components up to 250 mg m−2 along the transport paths, whereas the smoke aerosols in central Africa exhibited stronger light absorption (i.e., lower SSA) and lower AOD, resulting in higher-BC mass concentrations and similar BrC mass concentrations than the cases in North America. Seasonal burning source locations in central Africa, following the seasonal shift in the Intertropical Convergence Zone and diurnal variations in smoke amounts, were also captured. A comparison of retrieved AOD443, SSA443, SSA680, and ALH with collocated AERONET and CALIOP measurements shows agreement with RMSE values of 0.2, 0.03–0.04, 0.02–0.04, and 0.8–1.3 km, respectively. An analysis of the spatiotemporal average reveals distinct geographical characteristics in smoke properties closely linked to burning types and meteorological conditions. Forest wildfires over western North America generated smoke with a small-BC volume fraction of 0.011 and a high ALH with large variability (2.2 ± 1.2 km), whereas smoke from wildfires and agricultural burning over Mexico region shows more absorption and low ALH. Smoke from savanna fires over central Africa had the most absorption, with a high-BC volume fraction (0.015) and low ALH with a small variation (1.8 ± 0.6 km) among the analyzed regions. Tropical forest smoke was less absorbing and had a high variance in ALH. We also quantify the estimation uncertainties related to the assumptions of BC and BrC refractive indices. The MAIAC EPIC smoke properties with BC and BrC volume and mass fractions and assessment of the layer height provide observational constraints for radiative forcing modeling and air quality and health studies.

South American monsoon intensification during the last millennium driven by joint Pacific and Atlantic forcing

The South American summer monsoon (SASM) profoundly influences tropical South America’s climate, yet understanding its low-frequency variability has been challenging. Climate models and oxygen isotope data have been used to examine the SASM variability over the last millennium (LM) but have, at times, provided conflicting findings, especially regarding its mean-state change from the Medieval Climate Anomaly to the Little Ice Age. Here, we use a paleoclimate data assimilation (DA) method, combining model results and δ 18 O observations, to produce a δ 18 O-enabled, dynamically coherent, and spatiotemporally complete austral summer hydroclimate reconstruction over the LM for tropical South America at 5-year resolution. This reconstruction aligns with independent hydroclimate and δ 18 O records withheld from the DA, revealing a centennial-scale SASM intensification during the MCA-LIA transition period, associated with the southward shift of the Atlantic Intertropical Convergence Zone and the strengthening Pacific Walker circulation (PWC). This highlights the necessity of accurately representing the PWC in climate models to predict future SASM changes.

Emergent constraints on future Amazon climate change-induced carbon loss using past global warming trends

Reducing uncertainty in the response of the Amazon rainforest, a vital component of the Earth system, to future climate change is crucial for refining climate projections. Here we demonstrate an emergent constraint (EC) on the future response of the Amazon carbon cycle to climate change across CMIP6 Earth system models. Models that overestimate past global warming trends, tend to estimate hotter and drier future Amazon conditions, driven by northward shifts of the intertropical convergence zone over the Atlantic Ocean, causing greater Amazon carbon loss. The proposed EC changes the mean CMIP6 Amazon climate-induced carbon loss estimate (excluding CO2 fertilisation and land-use change impacts) from −0.27 (−0.59–0.05) to −0.16 (−0.42–0.10) GtC year−1 at 4.4 °C warming level, reducing the variance by 34%. This study implies that climate-induced carbon loss in the Amazon rainforest by 2100 is less than thought and that past global temperature trends can be used to refine regional carbon cycle projections.

Asymmetric ENSO teleconnections in a symmetric CO2 concentration pathway

Abstract El Niño-Southern Oscillation (ENSO) is the strongest interannual phenomenon occurring in tropical Pacific, significantly affecting the entire world. The ENSO response to increasing CO2 concentrations has been extensively studied, but the reverse scenario is still not well comprehended. Here, we investigate the hysteresis of ENSO teleconnections in a CO2 removal simulation of an earth system model. During the ramp-up periods of CO2 concentrations, Pacific-North American and Pacific-South American patterns are intensified, with the eastward shifts of their poles, which are even further intensified during the ramp-down period. This ENSO teleconnection hysteresis is closely linked to the tropical-origin hysteresis, in which during the ramp-down periods, the prevalence of eastern-Pacific type El Niño leads to the hysteresis in the eastern Hemispheric ENSO teleconnections and the enhanced ENSO skewness and the eastward shift of ENSO-induced tropical atmospheric convection do to that in the western Hemispheric ENSO teleconnection. The alterations by the tropical origin are predominantly associated with intensified southward migration of the Intertropical Convergence Zone, along with a stronger El Niño-like warming trend. We also demonstrated that the hysteretic change in the mid-latitude mean state over North Pacific region could lead to hysteresis of ENSO teleconnection without invoking the tropical origin.

Antarctic meltwater reduces the Atlantic meridional overturning circulation through oceanic freshwater transport and atmospheric teleconnections

The Atlantic meridional overturning circulation is an important component of the climate system because of its role in the heat transport. Its strength is sensitive to the surface density but mechanisms of the effect of Southern Ocean freshwater anomalies are relatively unknown. Here, we investigate the impact of Antarctic ice sheet meltwater on the Atlantic meridional overturning circulation using an earth system model of intermediate complexity. The meltwater over the Pacific sector of the Southern Ocean is transported to the east and, after passing the Drake Passage, travels northward reaching the North Atlantic. Furthermore, Southern Ocean cooling induces a northward shift of the Intertropical Convergence Zone, leading to more precipitation in the tropical Atlantic. Consequently, the reduced salinity weakens the Atlantic meridional overturning circulation. Additional experiments, in which the duration period of freshwater hosing was varied while keeping its total amount constant, indicate that the amplitude and the duration of the meltwater play crucial roles in determining the degree of reduction in Atlantic meridional overturning circulation.

SMOS captures variations in SSS fronts during El Niño and La Niña

The launch of the Soil Moisture and Ocean Salinity (SMOS) satellite has promoted research on sea surface salinity (SSS) and salinity fronts (SF). The SF in the central Pacific Ocean is influenced by El Niño and La Niña events, and the physical processes involved are complex. In this study, we evaluated the ability of the SMOS product from the Barcelona Expert Centre (BEC) to retrieve SF using a simple and intuitive method. Furthermore, this study investigated seasonal variations in the SF and its response to El Niño and La Niña events. The accuracy of the SMOS BEC L4 SSS is sufficient for studying SF. By selecting reasonable SF thresholds and analyzing its locations and intensities, in the central equatorial Pacific Ocean, SF can be divided into two: northern and southern SF. The variability in the northern SF is primarily influenced by the migration of the intertropical convergence zone (ITCZ), whereas both freshwater flux and salt advection are the primary factors in the southern SF. They correspond to El Niño and La Niña events through freshwater flux and salt advection. These findings can provide information for the study of the SF based on satellite data and enhance our understanding of El Niño Southern Oscillation (ENSO) dynamics.

The Role of Cloud-Radiative Interaction in Tropical Circulation and the Madden–Julian Oscillation

Abstract Cloud-radiative interaction (CRI) is a fundamental process that modulates tropical circulation and intraseasonal variability, including the Madden–Julian oscillation (MJO). In this study, we investigate how the mean state of the tropical atmosphere and the MJO respond to CRI intensity changes and provide insights into the underlying mechanisms, using the aquaplanet configuration in the Community Earth System Model, version 2 (CESM2). By enhancing CRI through tuning the DCS parameter (an autoconversion threshold size in the Morrison and Gettelman cloud microphysics scheme), we demonstrate that DCS-induced CRI intensification is linked to a warmer troposphere, increased tropical moisture, strengthened Hadley cell (HC), stronger trade winds, and a stronger equatorward intertropical convergence zone (ITCZ) with more clouds and precipitation, reflecting stronger cloud–radiation–circulation feedback. The intensified CRI also leads to the intensification and slower propagation of the simulated MJO-like mode despite the MJO-like signals becoming less distinguishable from the background due to the influence of other waves. The MJO intensification is likely associated with the mean state changes that support the development of deep convection. Moreover, the CRI itself, especially the interaction with the longwave radiation, also directly influences the MJO’s maintenance and propagation, more contributing to the maintenance of column moist static energy (MSE) and deceleration of its eastward propagation on intraseasonal time scales.

The Calm and Variable Inner Life of the Atlantic Intertropical Convergence Zone: The Relationship Between the Doldrums and Surface Convergence

AbstractThe doldrums are regions of low wind speeds and variable wind directions in the deep tropics that have been known for centuries. Although the doldrums are often associated with the Intertropical Convergence Zone (ITCZ), the exact relationship remains unclear. This study re‐examines the relationship between low‐level convergence and the Atlantic doldrums. By analyzing the frequency distribution of low wind speed events in reanalysis and buoy data, we show that the doldrums are largely confined between the edges of the ITCZ marked by enhanced surface convergence. While the region between the edges is a region of high time‐mean precipitation, low wind speed events occur in the absence of precipitation. Based on these results, we hypothesize that low wind speed events occur in regions of low level divergence rather than convergence.

Long-Term Validation of Aeolus Level-2B Winds in the Brazilian Amazon

The Atmospheric Dynamics Mission ADM-Aeolus was successfully launched in August 2018 by the European Space Agency (ESA). The Aeolus mission carried a single instrument, the first-ever Doppler wind lidar (DWL) in space, called Atmospheric LAser Doppler INstrument (ALADIN). Aeolus circled the Earth, providing vertical profiles of horizontal line-of-sight (HLOS) winds on a global scale. The Aeolus satellite’s measurements filled critical gaps in existing wind observations, particularly in remote regions such as the Brazilian Amazon. This area, characterized by dense rainforests and rich biodiversity, is essential for global climate dynamics. The weather patterns of the Amazon are influenced by atmospheric circulation driven by Hadley cells and the Intertropical Convergence Zone (ITCZ), which are crucial for the distribution of moisture and heat from the equator to the subtropics. The data provided by Aeolus can significantly enhance our understanding of these complex atmospheric processes. In this long-term validation study, we used radiosonde data collected from three stations in the Brazilian Amazon (Cruzeiro do Sul, Porto Velho, and Rio Branco) as a reference to assess the accuracy of the Level 2B (L2B) Rayleigh-clear and Mie-cloudy wind products. Statistical validation was conducted by comparing Aeolus L2B wind products and radiosonde data covering the period from October 2018 to March 2023 for Cruzeiro do Sul and Porto Velho, and from October 2018 to December 2022 for Rio Branco. Considering all available collocated winds, including all stations, a Pearson’s coefficient (r) of 0.73 was observed in Rayleigh-clear and 0.85 in Mie-cloudy wind products, revealing a strong correlation between Aeolus and radiosonde winds, suggesting that Aeolus wind products are reliable for capturing wind profiles in the studied region. The observed biases were −0.14 m/s for Rayleigh-clear and −0.40 m/s for Mie-cloudy, fulfilling the mission requirement of having absolute biases below 0.7 m/s. However, when analyzed annually, in 2022, the bias for Rayleigh-clear was −0.95 m/s, which did not meet the mission requirements.