The Amazonian Low-Level Jet and Its Connection to Convective Cloud Propagation and Evolution

Anselmo, Evandro M.; Schumacher, Courtney; Machado, Luiz A. T.

doi:10.1175/mwr-d-19-0414.1

Cited by 30 publications

(28 citation statements)

References 56 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…On ShCu days, easterlies are stronger in the boundary layer in the early morning, and become weaker at levels between 850 and 750 hPa in the afternoon when compared to Deep days (Figure 7c). The low-level easterly wind enhancement is consistent with the observation that the Amazonian nocturnal low-level jet is stronger when it reaches T3 (in the morning hours because of the time for the signal to propagate from the coast) on days that are less convectively active over the Amazon (Anselmo et al, 2020). There are also significant differences in the large-scale subsidence, which is stronger on ShCu days, especially in the afternoon and early evening (Figures 7b and 7d).…”

Section: Large-scale Wind and Wind Shearsupporting

confidence: 87%

Interpreting the Diurnal Cycle of Clouds and Precipitation in the ARM GoAmazon Observations: Shallow to Deep Convection Transition

et al. 2021

Self Cite

View full text Add to dashboard Cite

The Green Ocean Amazon (GoAmazon) 2014/5 field campaign data are used to study the diurnal cycle of clouds and precipitation. Through a careful classification of days with shallow cumulus, congestus and deep convection, we investigate the major differences among locally generated convection regimes and the most important environmental factors governing the shallow‐to‐deep convection transition. On shallow cumulus days, a greater sensible heat flux drives deeper boundary layer growth, which entrains drier free‐tropospheric air and lowers the relative humidity, thus leading to a significantly higher cloud base than those on days with deeper convection. Congestus and deep convection regimes exhibit distinct cloud top height distributions with noticeable differences in the vertical wind shear in the mid‐troposphere, suggesting an important role of wind shear in limiting the vertical extent of convection. On deep convection days, with preexisting nocturnal convection or cold‐pools from external disturbances, the timing of peak surface precipitation (12:00–13:00 LST) tends to be in‐phase with the diurnal variation in surface fluxes. However, it takes longer for local deep convection to develop without these disturbances. A plume model with thermodynamic and dynamical constraints is developed to explore the relative importance of various convection‐controlling factors. Initial cloud‐base vertical velocity and buoyancy are important in helping parcels ascend to the level of free convection (LFC). After parcels reach the LFC, entrainment of environmental air and lower free troposphere humidity become crucial in determining cloud top. Entrainment rate differentiates among convection regimes, which may be tied to the cloud size distribution at cloud base.

show abstract

Section: Large-scale Wind and Wind Shearsupporting

confidence: 87%

Interpreting the Diurnal Cycle of Clouds and Precipitation in the ARM GoAmazon Observations: Shallow to Deep Convection Transition

et al. 2021

Self Cite

View full text Add to dashboard Cite

show abstract

“…Using the AMCs dataset in this study jointly with the atmospheric flow as seen by reanalysis and the soundings during GoAmazon2014, Anselmo et al . (2020) showed that there is the impact of the nocturnal Amazonian low‐level jet (ALLJ) on the propagation and life cycle of convective systems from the northeast coast of South America into central Amazonia. The ALLJ can act in different ways to produce the observed break and reactivation of the convection, as for instance by advection of humidity from the coast overnight that assists daytime convection the next day or by association with internal gravity waves that can propagate as described by Sun and Orlanski (1981).…”

Section: Resultsmentioning

confidence: 99%

“…Amazonian mesoscale convective systems (AMCSs) are defined in this study as a general descriptor of organized convective cloud clusters observed in the Amazon basin and neighbouring regions, including the coast. AMCS propagation and evolution is complex and depends on several factors, such as the large‐scale circulation, topography, and river and sea breezes (e.g., Oliveira and Fitzjarrald, 1993; Cohen et al ., 1995; Anselmo et al ., 2020). For example, satellite studies generally report a predominantly westward propagation of convective systems across the Amazon basin associated with the easterly trade winds (e.g., Machado et al ., 1998; Rehbein et al ., 2017).…”

Section: Introductionmentioning

confidence: 99%

Amazonian mesoscale convective systems: Life cycle and propagation characteristics

Anselmo

Machado

Schumacher

et al. 2021

Intl Journal of Climatology

Self Cite

View full text Add to dashboard Cite

Convective system tracking was performed using 30‐min GOES‐13 infrared imagery over the Amazon region during 2014 and 2015. A total of 116,701 convective systems were identified and statistics on the probability of occurrence of track area, lifetime, and system velocity were analysed. Maps of the total and seasonal geographic density of trajectories and the geographic density of clusters at genesis, during propagation, and at dissipation were also assessed. The mean area and lifetime of the tracked systems was 4 × 104 km2 and 3 hr, respectively. The top 10% largest systems had areas >8 × 104 km2 and the top 10% longest lived systems lasted >7 hr. The geographical distribution of clusters identified on the coast and within the Amazon basin varied seasonally and their life cycle tracking showed that they are typically distinct from one another (i.e., it is relatively rare for systems to start at the coast and propagate 1,500 km to the centre of the basin). Although the average system velocity indicated a predominantly westward motion, a large spread in the direction of propagation was found. In particular, the probability of a meridional component of motion was generally the same for northward or southward directions and 35% of the zonal propagation was associated with eastward movement. The presence of Kelvin waves accounted for some of the eastward system motion, in addition to increasing the area and lifetime of storms compared to when Kelvin waves were not present.

show abstract

“…Montini et al (2019) discussed the better performance of the ERA-Interim compared with other reanalyzes to represent a vertical structure of the South American low-level jet. In addition, Anselmo et al (2020) found minor differences between the ERA-Interim and a modern and finer resolution reanalysis (MERRA-2) to reproduce a vertical structure of the low-level jet in the Amazon. They showed that the MERRA-2 low-level jet has a time of occurrence and vertical structure (with maximum wind speeds at 950 hPa) similar to local sounding observations, although it underestimates the wind intensity.…”

Section: Datamentioning

confidence: 92%

Assessing the Moisture Transports Associated With Nocturnal Low-Level Jets in Continental South America

Braz

Ambrizzi

Rocha

et al. 2021

Front. Environ. Sci.

View full text Add to dashboard Cite

Given the crucial role of low-level circulation in convective events, this study presents a climatological characterization of the moisture sources and sinks associated with the occurrence of nocturnal low-level jets (NLLJs) in South America. Six selected NLLJ cores are identified according to the jet index that considers a vertical wind speed shear of the lower troposphere at 00:00 local time (LT). The Lagrangian FLEXible PARTicle (FLEXPART) model was used to provide the outputs for tracking atmospheric air masses to determine the moisture sources and sinks for the NLLJ cores (Argentina, Venezuela, and the regions of Brazil: south—Brazil-S, southeast—Brazil-SE, north—Brazil-N, and northeast—Brazil-NE). The analysis is based on 37 years (1980–2016) of the ERA-Interim reanalysis. We found that the NLLJ index is stronger in the warm periods of a year (austral spring and summer) for the six selected regions. The NLLJ frequency is also higher in the warm months of the year, except in Brazil-NE where it is very frequent in all months. In Brazil-NE, the NLLJ also persists for 8 or more days, while the other NLLJs frequently persist for 1–2 days. The NLLJs occupy a broad low-level layer (from 1000 to 700 hPa) and exhibit a mean speed between 7 and 12 ms–1, which peaks mostly at 900 hPa. The moisture transport for each NLLJ shows that in addition to the intense local moisture sources, the NLLJs in Argentina and Brazil-S receive moisture from the tropical-subtropical South Atlantic Ocean and the Amazon basin, while the tropical-subtropical South Atlantic Ocean is the main moisture source for the NLLJ in Brazil-SE. Both moisture sources and sinks are stronger in the austral summer and fall. The NLLJ in Brazil receives moisture from the tropical South Atlantic (TSA) Ocean, which has weak seasonality. The moisture sources for the NLLJs in Brazil-N and Venezuela come from the tropical North Atlantic (TNA) Ocean in the austral summer and fall, while the TSA Ocean appears as an additional moisture source in the austral winter. This research contributes to improving our understanding of the NLLJs and their role in transporting moisture and controlling precipitation over the continent according to the seasons of a year, helping to improve seasonal climate forecasting.

show abstract

The Amazonian Low-Level Jet and Its Connection to Convective Cloud Propagation and Evolution

Cited by 30 publications

References 56 publications

Interpreting the Diurnal Cycle of Clouds and Precipitation in the ARM GoAmazon Observations: Shallow to Deep Convection Transition

Interpreting the Diurnal Cycle of Clouds and Precipitation in the ARM GoAmazon Observations: Shallow to Deep Convection Transition

Amazonian mesoscale convective systems: Life cycle and propagation characteristics

Assessing the Moisture Transports Associated With Nocturnal Low-Level Jets in Continental South America

Contact Info

Product

Resources

About