Tropical precipitation–buoyancy relationship in Convectively Coupled Waves over South America region

2020 ◽  
Author(s):  
Victor Mayta ◽  
Angel Adames
Keyword(s):  
South America ◽  
Lower Troposphere ◽  
Coupling Mechanism ◽  
Wet Season ◽  
Thermodynamic Structure ◽  
Equatorial Wave ◽  
Tropical Wave ◽  
Static Energy ◽  
Daily Wave ◽  
Open Question

<p>In this work, the tropical wave precipitation-buoyancy relationship is revisited by analyzing 4-times daily wave-filtered brightness temperature, reanalysis, and radiosonde datasets over tropical South America during the wet season. Prior studies demonstrated that an integrated measure of buoyancy well-diagnoses precipitation over land and ocean. However, it is an open question whether the buoyancy-based approach can yield a robust relation to precipitation for equatorial wave disturbances. To advance our understanding of this relationship, a comprehensive analysis of their vertical thermodynamic structure and potential interactions with the basic state is also presented. An emphasis is placed on understanding the convection coupling mechanism in convectively coupled Kelvin and inertia-gravity waves. It will be shown that buoyancy is a better predictor of convection for these disturbances than the often-used moist static energy (MSE). Examination of this discrepancy reveals that a cooling of the lower troposphere by gravity wave motions, which reduces MSE, is key to the production of precipitation in these disturbances.</p>

scholarly journals A Moist Static Energy Budget–Based Analysis of the Sahel Rainfall Response to Uniform Oceanic Warming

2017 ◽  
Vol 30 (15) ◽  
pp. 5637-5660 ◽  
Author(s):  
Spencer A. Hill ◽  
Yi Ming ◽  
Isaac M. Held ◽  
Ming Zhao
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Order Term ◽  
Lower Troposphere ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Moist Static Energy ◽  
Wet Season ◽  
Wide Range ◽  
Sst Warming ◽  
Static Energy

Climate models generate a wide range of precipitation responses to global warming in the African Sahel, but all that use the NOAA Geophysical Fluid Dynamics Laboratory AM2.1 model as their atmospheric component dry the region sharply. This study compares the Sahel’s wet season response to uniform 2-K SST warming in AM2.1 using either its default convective parameterization, relaxed Arakawa–Schubert (RAS), or an alternate, the University of Washington (UW) parameterization, using the moist static energy (MSE) budget to diagnose the relevant mechanisms. UW generates a drier, cooler control Sahel climate than does RAS and a modest rainfall increase with SST warming rather than a sharp decrease. Horizontal advection of dry, low-MSE air from the Sahara Desert—a leading-order term in the control MSE budget with either parameterization—is enhanced with oceanic warming, driven by enhanced meridional MSE and moisture gradients spanning the Sahel. With RAS, this occurs throughout the free troposphere and is balanced by anomalous MSE import through anomalous subsidence, which must be especially large in the midtroposphere where the moist static stability is small. With UW, the strengthening of the meridional MSE gradient is mostly confined to the lower troposphere, due in part to comparatively shallow prevailing convection. This necessitates less subsidence, enabling convective and total precipitation to increase with UW, although both large-scale precipitation and precipitation minus evaporation decrease. This broad set of hydrological and energetic responses persists in simulations with SSTs varied over a wide range.

scholarly journals Medium-range mid-tropospheric transport of ozone and precursors over Africa: two numerical case studies in dry and wet seasons

2007 ◽  
Vol 7 (20) ◽  
pp. 5357-5370 ◽  
Author(s):  
B. Sauvage ◽  
F. Gheusi ◽  
V. Thouret ◽  
J.-P. Cammas ◽  
J. Duron ◽  
...  
Keyword(s):  
Mirror Symmetry ◽  
Monsoon Season ◽  
Trade Flow ◽  
Lower Troposphere ◽  
Hadley Cell ◽  
Scale Model ◽  
Wet Season ◽  
Airborne Measurements ◽  
Ozone Precursors ◽  
Low Level

Abstract. A meso-scale model was used to understand and describe the dynamical processes driving high ozone concentrations observed during both dry and monsoon season in monthly climatologies profiles over Lagos (Nigeria, 6.6° N, 3.3° E), obtained with the MOZAIC airborne measurements (ozone and carbon monoxide). This study focuses on ozone enhancements observed in the upper-part of the lower troposphere, around 3000 m. Two individual cases have been selected in the MOZAIC dataset as being representative of the climatological ozone enhancements, to be simulated and analyzed with on-line Lagrangian backtracking of air masses. This study points out the role of baroclinic low-level circulations present in the Inter Tropical Front (ITF) area. Two low-level thermal cells around a zonal axis and below 2000 m, in mirror symmetry to each other with respect to equator, form near 20° E and around 5° N and 5° S during the (northern hemisphere) dry and wet seasons respectively. They are caused by surface gradients – the warm dry surface being located poleward of the ITF and the cooler wet surface equatorward of the ITF. A convergence line exists between the poleward low-level branch of each thermal cell and the equatorward low-level branch of the Hadley cell. Our main conclusion is to point out this line as a preferred location for fire products – among them ozone precursors – to be uplifted and injected into the lower free troposphere. The free tropospheric transport that occurs then depends on the hemisphere and season. In the NH dry season, the AEJ allows transport of ozone and precursors westward to Lagos. In the NH monsoon (wet) season, fire products are transported from the southern hemisphere to Lagos by the southeasterly trade that surmounts the monsoon layer. Additionally ozone precursors uplifted by wet convection in the ITCZ can also mix to the ones uplifted by the baroclinic cell and be advected up to Lagos by the trade flow.

scholarly journals Impacts of Shallow Convection on MJO Simulation: A Moist Static Energy and Moisture Budget Analysis

2013 ◽  
Vol 26 (8) ◽  
pp. 2417-2431 ◽  
Author(s):  
Qiongqiong Cai ◽  
Guang J. Zhang ◽  
Tianjun Zhou
Keyword(s):  
Boundary Layer ◽  
Deep Convection ◽  
Lower Troposphere ◽  
Longwave Radiation ◽  
Reanalysis Data ◽  
Specific Humidity ◽  
Moist Static Energy ◽  
Shallow Convection ◽  
Budget Analysis ◽  
Static Energy

Abstract The role of shallow convection in Madden–Julian oscillation (MJO) simulation is examined in terms of the moist static energy (MSE) and moisture budgets. Two experiments are carried out using the NCAR Community Atmosphere Model, version 3.0 (CAM3.0): a “CTL” run and an “NSC” run that is the same as the CTL except with shallow convection disabled below 700 hPa between 20°S and 20°N. Although the major features in the mean state of outgoing longwave radiation, 850-hPa winds, and vertical structure of specific humidity are reasonably reproduced in both simulations, moisture and clouds are more confined to the planetary boundary layer in the NSC run. While the CTL run gives a better simulation of the MJO life cycle when compared with the reanalysis data, the NSC shows a substantially weaker MJO signal. Both the reanalysis data and simulations show a recharge–discharge mechanism in the MSE evolution that is dominated by the moisture anomalies. However, in the NSC the development of MSE and moisture anomalies is weaker and confined to a shallow layer at the developing phases, which may prevent further development of deep convection. By conducting the budget analysis on both the MSE and moisture, it is found that the major biases in the NSC run are largely attributed to the vertical and horizontal advection. Without shallow convection, the lack of gradual deepening of upward motion during the developing stage of MJO prevents the lower troposphere above the boundary layer from being preconditioned for deep convection.

The Moist Static Energy Budget of a Composite Tropical Intraseasonal Oscillation in a Climate Model

2009 ◽  
Vol 22 (3) ◽  
pp. 711-729 ◽  
Author(s):  
Eric D. Maloney
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Climate Model ◽  
Intraseasonal Variability ◽  
Lower Troposphere ◽  
Specific Humidity ◽  
Horizontal Advection ◽  
Moisture Advection ◽  
Static Energy

Abstract The intraseasonal moist static energy (MSE) budget is analyzed in a climate model that produces realistic eastward-propagating tropical intraseasonal wind and precipitation variability. Consistent with the recharge–discharge paradigm for tropical intraseasonal variability, a buildup of column-integrated MSE occurs within low-level easterly anomalies in advance of intraseasonal precipitation, and a discharge of MSE occurs during and after precipitation when westerly anomalies occur. The strongest MSE anomalies peak in the lower troposphere and are, primarily, regulated by specific humidity anomalies. The leading terms in the column-integrated intraseasonal MSE budget are horizontal advection and surface latent heat flux, where latent heat flux is dominated by the wind-driven component. Horizontal advection causes recharge (discharge) of MSE within regions of anomalous equatorial lower-tropospheric easterly (westerly) anomalies, with the meridional component of the moisture advection dominating the MSE budget near 850 hPa. Latent heat flux anomalies oppose the MSE tendency due to horizontal advection, making the recharge and discharge of column MSE more gradual than if horizontal advection were acting alone. This relationship has consequences for the time scale of intraseasonal variability in the model. Eddies dominate intraseasonal meridional moisture advection in the model. During periods of low-level intraseasonal easterly anomalies, eddy kinetic energy (EKE) is anomalously low due to a suppression of tropical synoptic-scale disturbances and other variability on time scales shorter than 20 days. Anomalous moistening of the equatorial lower troposphere occurs during intraseasonal easterly periods through suppression of eddy moisture advection between the equator and poleward latitudes. During intraseasonal westerly periods, EKE is enhanced, leading to anomalous drying of the equatorial lower troposphere through meridional advection. Given the importance of meridional moisture advection and wind-induced latent heat flux to the intraseasonal MSE budget, these findings suggest that to simulate realistic intraseasonal variability, climate models must have realistic basic-state distributions of lower-tropospheric zonal wind and specific humidity.

scholarly journals Evidence of the complexity of aerosol transport in the lower troposphere on the Namibian coast during AEROCLO-sA

2019 ◽  
Author(s):  
Patrick Chazette ◽  
Cyrille Flamant ◽  
Julien Totems ◽  
Marco Gaetani ◽  
Gwendoline Smith ◽  
...  
Keyword(s):  
South America ◽  
Sea Level ◽  
Complex Mixture ◽  
Lower Troposphere ◽  
Back Trajectory ◽  
Aerosol Layer ◽  
Free Troposphere ◽  
Aerosol Composition ◽  
Mean Sea Level ◽  
Field Campaign

Abstract. The evolution of the vertical distribution and optical properties of aerosols in the free troposphere, above stratocumulus, is analysed for the first time over the Namibian coast, a region where uncertainties on aerosol-cloud coupling in climate simulations are significant. We show the high variability of atmospheric aerosol composition in the lower and middle troposphere during the AEROCLO-sA field campaign (22 August–12 September 2017) around the Henties Bay supersite, using a combination of ground-based, airborne and space-borne lidar measurements. Three distinct periods of 4 to 7 days are observed, associated with increasing aerosol loads (aerosol optical thickness at 550 nm ranging from ~ 0.2 to ~ 0.7), as well as increasing aerosol layer depth and top altitude. Aerosols are observed up to 6 km above mean sea level during the later period. Aerosols transported within the free troposphere are mainly polluted dust (dust mixed with smoke from fires in Angola) for the first 2 periods (22 August–1 September 2017) and smoke (from Angola and South America) for the last part (3–9 September) of the field campaign. Lagrangian back trajectory analyses highlight that the highest aerosol layers (between 5 and 6 km above mean sea level) come from South America (Brazil, Argentina and Paraguay) and reach Henties Bay after 4 to 5 days. They are transported eastward by the mid latitude westerlies and towards Southern Africa by the equatorward moving cut-off low originating within the westerlies. This results in a very complex mixture of aerosols over the coastal regions of Namibia that must be taken into account when investigating aerosols radiative effects above stratocumulus clouds in the south east Atlantic Ocean.

scholarly journals Tropospheric ozone over Equatorial Africa: regional aspects from the MOZAIC data

2005 ◽  
Vol 5 (2) ◽  
pp. 311-335 ◽  
Author(s):  
B. Sauvage ◽  
V. Thouret ◽  
J.-P. Cammas ◽  
F. Gheusi ◽  
G. Athier ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Central Africa ◽  
Lower Troposphere ◽  
Dry Season ◽  
Vertical Profiles ◽  
Gulf Of Guinea ◽  
Wet Season ◽  
Monthly Basis ◽  
Regional Flow ◽  
Equatorial Africa

Abstract. We analyze ozone observations recorded over Equatorial Africa between April 1997 and March 2003 by the MOZAIC programme, providing the first ozone climatology deriving from continental in-situ data over this region. Three-dimensional streamlines strongly suggests connections between the characteristics of the ozone monthly mean vertical profiles, the most persistent circulation patterns in the troposphere over Equatorial Africa (on a monthly basis) such as the Harmattan, the African Easterly Jet, the Trades and the regions of ozone precursors emissions by biomass burning. During the biomass burning season in each hemisphere, the lower troposphere exhibits layers of enhanced ozone (i.e. 70 ppbv over the coast of Gulf of Guinea in December-February and 85 ppbv over Congo in June-August). The characteristics of the ozone monthly mean vertical profiles are clearly connected to the regional flow regime determined by seasonal dynamic forcing. The mean ozone profile over the coast of Gulf of Guinea in the burning season is characterized by systematically high ozone below 650hPa ; these are due to the transport by the Harmattan and the AEJ of the pollutants originating from upwind fires. The confinement of high ozone to the lower troposphere is due to the high stability of the Harmattan and the blocking Saharan anticyclone which prevents efficient vertical mixing. In contrast, ozone enhancements observed over Central Africa during the local dry season (June-August) are not only found in the lower troposphere but throughout the troposphere. Moreover, this study highlights a connection between the regions of the coast of Gulf of Guinea and regions of Congo to the south that appears on a semi annual basis. Vertical profiles in wet-season regions exhibit ozone enhancements in the lower troposphere due to biomass burning products transport from fires situated in the opposite dry-season hemisphere.

First Amburana cearensis (Fabaceae) tree-ring chronology in Brazil in a dry forest shows great potential for climate reconstruction

2020 ◽  
Author(s):  
Milena Godoy-Veiga ◽  
Giuliano Locosselli ◽  
Lior Regev ◽  
Elisabetta Boaretto ◽  
Gregório Ceccantini
Keyword(s):  
South America ◽  
Tree Ring ◽  
Negative Correlation ◽  
Ring Width ◽  
Dry Forest ◽  
Tree Ring Width ◽  
Wet Season ◽  
Seasonally Dry ◽  
Spatial Coverage ◽  
Standard Tree

<p>Tree-ring chronologies are an excellent climate archive for their spatial and temporal resolution. While networks of chronologies have been built outside the tropics helping to understand past regional climate trends, tropical regions still lag behind in terms of spatial coverage. Dendrochronological studies, however, may succeed in seasonally dry tropical forests where the growing season is well defined. <em>Amburana cearensis</em>, found in both dry and wet forests in South America, is poorly explored for dendrochronological purposes, with no previous study in Brazil. Therefore, we sampled trees growing in a seasonally dry forest in a karstic area in Central-Eastern Brazil, under the South American Monsoon domain, in order to explore this species potential for dendroclimatological studies in the region. We build a tree-ring width chronology using 26 trees. We found a strong common growth signal among trees, with an r-bar of 0.51 and an average mean sensitivity of 0.50. The standard tree-ring width chronology showed a significant negative correlation with Vapor-Pressure Deficit during the entire wet season (0.54), negative correlation with temperature at the end of the wet season (0.45), and a positive correlation with the sum of precipitation during the wet season (0.46). Further stable isotopic analysis will provide additional records of climate variability in the region. Since Amburana cearensis occurs across most of the seasonally dry forests and savannas from South America, it has a great potential to be used to develop climate reconstructions and verify the effects of climate change currently affecting the region.</p>

scholarly journals Large and increasing methane emissions from Eastern Amazonia derived from satellite data, 2010–2018

2020 ◽  
Author(s):  
Chris Wilson ◽  
Martyn P. Chipperfield ◽  
Manuel Gloor ◽  
Robert J. Parker ◽  
Hartmut Boesch ◽  
...  
Keyword(s):  
South America ◽  
Satellite Data ◽  
Amazon Basin ◽  
Fossil Fuels ◽  
Positive Trend ◽  
Wet Season ◽  
Ch4 Emissions ◽  
Vertical Profiling ◽  
Independent Observations ◽  
Global Increase

Abstract. We use a global inverse model, satellite data and flask measurements to estimate methane (CH4) emissions from South America, Brazil and the basin of the Amazon River for the period 2010–2018. We find that emissions from Brazil have risen during this period, most quickly in the Eastern Amazon Basin, and that this concurrent with increasing surface temperatures in this region. Brazilian CH4 emissions rose from 49.8 ± 5.4 Tg(CH4)/yr in 2010–2013 to 55.6 ± 5.2 Tg(CH4)/yr in 2014–2017, with the wet season of December–March having the largest positive trend in emissions. We derive no significant trend in regional emissions from fossil fuels during this period. We find that our posterior distribution of emissions within South America is significantly and consistently changed from our prior estimates, with the strongest emission sources being in the far north of the continent and to the south and south-east of the Amazon Basin, near the mouth of the Amazon and in other wetland regions. We derive particularly large emissions during the wet season of 2013/14, when flooding was prevalent over larger regions than normal within the Amazon Basin. We compare our posterior CH4 mole fractions, derived from posterior fluxes, to independent observations of CH4 mole fraction taken at five lower to mid tropospheric vertical profiling sites over the Amazon and find that our posterior fluxes outperform prior fluxes at all locations. In particular the large emissions from the eastern Basin are shown to be in good agreement with independent observations made at Santarém, a location which has long displayed higher mole fractions of atmospheric CH4 in contrast with other Basin locations. We show that a bottom-up flux model cannot match the variation in annual fluxes, nor the positive trend in emissions, produced by the inversion. Our results show that the Amazon alone was responsible for 24 ± 18 % of the total global increase in CH4 flux during the study period, and it may contribute further in future due to its sensitivity to temperature changes.

scholarly journals Projected End-of-Century Changes in the South American Monsoon in the CESM Large Ensemble

2020 ◽  
Vol 33 (18) ◽  
pp. 7859-7874
Author(s):  
Ana Claudia Thome Sena ◽  
Gudrun Magnusdottir
Keyword(s):  
South America ◽  
South Atlantic ◽  
Northeastern Brazil ◽  
Southeastern Brazil ◽  
South American ◽  
The South ◽  
Wet Season ◽  
Large Ensemble ◽  
South American Monsoon ◽  
The Mean

AbstractProjected changes in the South American monsoon system by the end of the twenty-first century are analyzed using the Community Earth System Model Large Ensemble (CESM-LENS). The wet season is shorter in LENS when compared to observations, with the mean onset occurring 19 days later and the mean retreat date 21 days earlier in the season. Despite a precipitation bias, the seasonality of rainfall over South America is reproduced in LENS, as well as the main circulation features associated with the development of the South American monsoon. Both the onset and retreat of the wet season over South America are delayed in the future compared to current climate by 3 and 7 days, respectively, with a slightly longer wet season. Central and southeastern Brazil are projected to get wetter as a result of moisture convergence from the strengthening of the South Atlantic low-level jet and a weaker South Atlantic subtropical high. The Amazon is projected to get drier by the end of the century, negatively affecting rain forest productivity. During the wet season, an increase in the frequency and intensity of extreme precipitation events is found over most of South America, and especially over northeastern and southern Brazil and La Plata. Meanwhile, during the dry season an increase in the maximum number of consecutive dry days is found over northeastern Brazil and the northern Amazon.

scholarly journals Two years of Ozone radio soundings over Cotonou as part of AMMA: overview

2009 ◽  
Vol 9 (3) ◽  
pp. 11221-11268 ◽  
Author(s):  
V. Thouret ◽  
M. Saunois ◽  
A. Minga ◽  
A. Mariscal ◽  
B. Sauvage ◽  
...  
Keyword(s):  
West Africa ◽  
Biomass Burning ◽  
Lower Stratosphere ◽  
Lower Troposphere ◽  
Data Sets ◽  
Wet Season ◽  
Data Set ◽  
In Situ Data ◽  
Multidisciplinary Analysis ◽  
First Time

Abstract. As part of the African Monsoon Multidisciplinary Analysis (AMMA) program, a total of 98 ozone vertical profiles over Cotonou, Benin, have been measured during a 26 month period (December 2004–January 2007). These regular measurements broadly document the seasonal and inter annual variability of ozone in both the troposphere and the lower stratosphere over West Africa for the first time. This data set is complementary to the MOZAIC observations made from Lagos between 0 and 12 km during the period 1998–2004. Both data sets highlight the unique way in which West Africa is impacted by two biomass burning seasons: in December–February (dry season) due to burning in the Sahelian band and in June–August (wet season) due to burning in southern Africa. High inter annual variabilities between Cotonou and Lagos data sets and within each data set are observed and are found to be a major characteristic of this region. In particular, the dry and wet seasons are discussed in order to set the data of the Special Observing Periods (SOPs) into a climatological context. Compared to other dry and wet seasons, the dry and wet season campaigns took place in rather high ozoneenvironments. During the sampled wet seasons, southern intrusions of biomass burning were particularly frequent with concentrations up to 120 ppbv of ozone in the lower troposphere. An insight into the ozone distribution in the upper troposphere and the lower stratosphere (up to 26 km) is given. The first tropospheric columns of ozone based on in-situ data in this region are assessed. They compare well with satellite products on seasonal and inter annual time-scales, provided that the layer below 850 Pa where the remote instrument is less sensitive to ozone, is removed.

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