Trade Winds Research Articles

A Reinforcement Learning approach for the continuous electricity market of Germany: Trading from the perspective of a wind park operator

With the rising extension of renewable energies, the intraday electricity markets have recorded a growing popularity amongst traders as well as electric utilities to cope with the induced volatility of the energy supply. Through their short trading horizon and continuous nature, the intraday markets offer the ability to adjust trading decisions from the day-ahead market or reduce trading risk in a short-term notice. Producers of renewable energies utilize the intraday market to lower their forecast risk, by modifying their provided capacities based on current forecasts. However, the market dynamics are complex due to the fact that the power grids have to remain stable and electricity is only partly storable. Consequently, robust and intelligent trading strategies are required that are capable to operate in the intraday market. In this work, we propose a novel autonomous trading approach based on Deep Reinforcement Learning (DRL) algorithms as a possible solution. For this purpose, we model the intraday trade as a Markov Decision Process (MDP) and employ the Proximal Policy Optimization (PPO) algorithm as our DRL approach. A simulation framework is introduced that enables the trading of the continuous intraday price in a resolution of one minute steps. We test our framework in a case study from the perspective of a wind park operator. We include next to general trade information both price and wind forecasts. On a test scenario of German intraday trading results from 2018, we are able to outperform multiple baselines with at least 45.24% improvement, showing the advantage of the DRL algorithm. However, we also discuss limitations and enhancements of the DRL agent, in order to increase the performance in future works.

A Review Paper on El Nino

El Nino episodes are major climatic disruptions that occur every 2 to 8 years and originate in the equatorial Pacific Ocean. From the coastlines of Peru and Ecuador to the middle of the equatorial Pacific Ocean, unusually warm waters at the ocean surface mark the developed phase of El Nino. The reason of this occurrence is a peculiar lessening of the westward blowing trade winds, which enables warm surface waters to reverse their course eastward. El Nino's climatic effects are increasing throughout the globe, and this may have a variety of consequences on regional weather. It is linked to a broad range of changes in the climate system, and it has the potential to have significant socio-economic consequences in the infrastructure, agricultural, health, and energy sectors. Despite the fact that El Nino occurs in the tropical Pacific, it has an effect on worldwide climate and weather events such as drought, floods, and tropical storms. The usual state in the equatorial Pacific has altered because of increased greenhouse gas emissions, which has resulted in changes in the El Nino Southern Oscillation (ENSO). ENSO fluctuations will continue to exist and affect global climate conditions in the future decades and millennia, we can be certain. As a result, both scientists and the public rely on predicting and understanding ENSO conditions. The occurrence of El Nino and its effect on world climate and socio-economic status have been researched and discussed in this article.

Shallow Cumulus Properties as Captured by Adiabatic Fraction in High-Resolution LES Simulations

AbstractShallow convective clouds are important players in Earth’s energy budget and hydrological cycle, and are abundant in the tropical and subtropical belts. They greatly contribute to the uncertainty in climate predictions due to their unresolved, complex processes that include coupling between the dynamics and microphysics. Analysis of cloud structure can be simplified by considering cloud motions as a combination of moist adiabatic motions like adiabatic updrafts and turbulent motions leading to deviation from adiabaticity. In this work, we study the sizes and occurrence of adiabatic regions in shallow cumulus clouds during their growth and mature stages, and use the adiabatic fraction (AF) as a continuous metric to describe cloud processes and properties from the core to the edge. To do so, we simulate isolated trade wind cumulus clouds of different sizes using the System of Atmospheric Modeling (SAM) model in high resolution (10 m) with the Hebrew University spectral bin microphysics (SBM). The fine features in the clouds’ dynamics and microphysics, including small near-adiabatic volumes and a thin transition zone at the edge of the cloud (∼20–40 m in width), are captured. The AF is shown to be an efficient measure for analyzing cloud properties and key processes determining the droplet-size distribution formation and shape during the cloud evolution. Physical processes governing the properties of droplet size distributions at different cloud regions (e.g., core, edge) are analyzed in relation to AF.Significance Statement1) This study investigates the evolution of cumulus clouds (Cu) using a 10-m-resolution LES model with spectral bin microphysics. 2) The study improves the understanding of the mutual effects of adiabatic updrafts and lateral entrainment and mixing. 3) The study demonstrates the existence of an adiabatic core in nonprecipitating Cu. 4) Shapes of the droplet size distributions are closely related to the adiabatic fraction values. 5) Utilization of high resolution reveals the existence of physically significant small features in the cloud structure, such as a narrow cloud interface zone and small adiabatic volumes.

The Spatial Separation of Callistopteris baldwinii (Hymenophyllaceae) Sporophytes and Gametophytes Along Elevational Gradients in Hawai‘i

Ferns and lycophytes are unique among land plants in having two independent life stages, the haploid gametophyte generation and the diploid sporophyte generation. While in most species the sporophyte is the dominant, long-lived portion of the life cycle, in some ferns the gametophyte is capable of sustained vegetative growth, and a number of species produce sporophytes only in parts of their geographic range (a pattern known as the separation of generations). One such species is the Hawaiian filmy fern Callistopteris baldwinii, whose growth form varies across elevational gradients. This species occurs as independent gametophytes near sea level, produces dwarfed sporophytes at mid elevations, and at the highest elevations—where precipitation is greatest due to the orographic uplift of trade winds—it grows as large, mature sporophytes. We measured temperature, relative humidity, and precipitation for several populations of this fern on the island of O‘ahu in Hawai‘i to determine whether these environmental factors may influence the spatial separation of generations exhibited by C. baldwinii on the island. Our results indicate that temperature and precipitation vary across life stages of C. baldwinii, underscoring the key role environmental conditions play in the completion of the fern life cycle.

Obliquity Influence on Low‐Latitude Coastal Precipitation in Eastern Brazil During the Past ∼850 kyr

AbstractPaleoclimate records from tropical South America typically show precession‐paced variability in rainfall, caused by insolation‐driven changes in the South American Monsoon System, however this mechanism may not be responsible for hydroclimate change outside of the core monsoon domain, such as in the coastal zone of tropical eastern Brazil. Our findings are based on a ∼850 kyr‐long multiproxy record from a marine sediment core collected from the eastern Brazilian margin that represents the longest continuous record of South American hydroclimate to date. Utilizing the ln (K/Al) chemical weathering proxy from the core, we determine that past hydroclimate change in the coastal zone was primarily modulated by obliquity forcing. We demonstrate that high obliquity is associated with an increase in the boreal summer interhemispheric insolation contrast which decreases the zonality of the southern trade winds and reduces moisture advection to the coastal zone. Based on the long‐term coherence between the ln (K/Al) record and benthic δ13C records from the Atlantic during Marine Isotope Stages 16–13, we infer that an increase in the strength of the overturning circulation, caused by Northern Hemisphere high‐latitude forcing, may have produced surface cooling in the western tropical South Atlantic which led to reduced moisture advection to the coastal zone. We suggest that this mechanism may have also caused the amplification in millennial‐scale variability in the coastal hydroclimate system, which began after the decoupling of the coastal hydroclimate system from obliquity forcing.

Wave-induced sediment and rhodolith mobility on a narrow insular shelf dominated by wave variability (Fernando de Noronha Archipelago, Brazil)

This study combines numerical modeling and empirical equations to define spatial fields of wave-induced sediment and rhodolith mobility in a narrow insular shelf that is subject to a seasonal wave regime: the Fernando de Noronha insular shelf. From analyses of the annual, summer and winter wave climates, we noticed an intense directional variability in swell waves coming predominantly from opposing directions between the studied seasons (northern swell in summer and southern swell in winter), reflecting higher wave energy on the north coast during summer and lower energy during winter. The longitudinal transport at the northern coast, which is predominantly oriented to the southwest, is also higher in the summer months and lower in the rest of the year. To describe the spatial variation in wave-induced mobility under summer and winter wave conditions, we consider empirical sediment movement equations, based on mean grain size and density values. Carbonate bioclastic sediments, which are predominant in the Fernando de Noronha shelf, are remobilized by waves throughout the entire shelf. However, in the nearshore zone, this movement occurs intensely for all sizes. The depth and shelf side affected by wave-induced mobility vary according to the wave climate variability that determines the direction and type of wave prevailing in the regime. When swell waves come from the north (summer scenarios), mobility is greater mainly on the northern shelf; however, when trade wind waves come from the southeast and swell waves come from the south (winter scenarios), greater movement is produced on the south face. Wave-induced sediment mobility occurs at depths of up to 60 m, near the shelf break, indicating the importance of the shelf morphology. The movement of rhodoliths, which presents a lower density and larger diameter than the sediments, eventually occurs under extreme wave conditions up to depths of approximately 30 m in areas that vary seasonally around the island according to the predominant wave direction. These characteristics are favorable to rhodolith development. With our results, we hope to better understand the wave action on the bottoms of high-energy island shelves by identifying the sediment movement patterns attributed to wave climate variability and morphological characteristics of the shelf.

Weakened impact of the Atlantic Niño on the future equatorial Atlantic and Guinea Coast rainfall

Abstract. The Guinea Coast is the southern part of the West African continent. Its summer rainfall variability mostly occurs on interannual timescales and is highly influenced by the sea surface temperature (SST) variability in the eastern equatorial Atlantic, which is the centre of action of the Atlantic Niño mode. Using both historical and scenario (SSP5–8.5) simulations from 31 general circulation models (GCMs) participating in the sixth phase of the Coupled Model Intercomparison Project (CMIP6), we first show that these models present a wet bias during boreal summer. This bias is associated with overly high mean boreal summer SSTs in the eastern equatorial and south Atlantic regions. Next, we analyse the near-term, mid-term and long-term changes of the Atlantic Niño relative to the present-day situation, in a climate with a high anthropogenic emission of greenhouse gases. We find a gradual decrease in the equatorial Atlantic SST anomalies associated with the Atlantic Niño in the future. This result reflects a possible reduction of the Atlantic Niño variability in the future due to a weakening of the Bjerknes feedback over the equatorial Atlantic. In a warmer climate, an anomalous higher sea level pressure in the western equatorial Atlantic relative to the eastern equatorial Atlantic weakens the climatological trade winds over the equatorial Atlantic. As a result, the eastern equatorial Atlantic thermocline is deeper and responds less to the Atlantic Niño events. Among the models that simulate a realistic rainfall pattern associated with the Atlantic Niño in the present-day climate, there are 12 GCMs which project a long-term decrease in the Guinea Coast rainfall response related to the Atlantic Niño. In these models, the zonal 850 hPa wind response to the Atlantic Niño over the equatorial Atlantic is strongly attenuated in the future climate. We also find that 12 other GCMs show no robust change in the patterns associated with the Atlantic Niño. There is a higher confidence in the mid-term and long-term reduction of the rainfall associated with the Atlantic Niño over the Atlantic Ocean than over the Guinea Coast. We also found a projected decrease in the convection associated with the Atlantic Niño in the majority of the models.

Mesoscale spatio-temporal variability of airborne lidar-derived aerosol properties in the Barbados region during EUREC<sup>4</sup>A

Abstract. From 23 January to 13 February 2020, 20 ATR-42 scientific flights were conducted in the framework of the EUREC4A field campaign over the tropical Atlantic, off the coast of Barbados (13∘30′ N, −58∘30′ W). By means of a sideway-pointing lidar, these flights allowed us to retrieve the optical properties of the aerosols found in the sub-cloud layer and below the trade wind inversion. Two distinct periods with significant aerosol contents were identified in relationship with the so-called trade wind and tropical regimes, respectively. For these two regimes, mixings of two air mass types encompassing dust and carbonaceous aerosols have been highlighted. Both were mainly from West Africa with similar optical contributions and linked to dust uptake above Sahara and biomass burning between Guinea-Bissau and Côte d'Ivoire. In the tropical transport regime, the wind within the planetary boundary layer is stronger and favours a contribution of marine aerosols (sulfate and sea salt aerosol components) in shallower aerosol layers than for the trade wind transport regime. The latter is responsible for advecting dust–biomass-burning-aerosol mixtures in the deeper, well-mixed layer, in part due to the complex interactions of the easterly flow from West Africa with mid-latitude dynamics. The aerosol vertical structures appear to be well reproduced using atmospheric composition reanalyses from CAMS when comparing with lidar-derived vertical profiles. The competition between the two types of transport regimes leads to strong heterogeneity in the optical properties of the horizontal aerosol field. Our study highlights the transport regime under which a significant mixture of dust and biomass burning aerosols from West Africa can be observed over the Caribbean and Barbados in particular, namely the trade wind regime.

Use of large-eddy simulations to design an adaptive sampling strategy to assess cumulus cloud heterogeneities by remotely piloted aircraft

Abstract. Trade wind cumulus clouds have a significant impact on the Earth's radiative balance due to their ubiquitous presence and significant coverage in subtropical regions. Many numerical studies and field campaigns have focused on better understanding the thermodynamic, microphysical, and macroscopic properties of cumulus clouds with ground-based and satellite remote sensing as well as in situ observations. Aircraft flights have provided a significant contribution, but their resolution remains limited by rectilinear transects and fragmented temporal data for individual clouds. To provide a higher spatial and temporal resolution, remotely piloted aircraft (RPA) can now be employed for direct observations using numerous technological advances to map the microphysical cloud structure and to study entrainment mixing. In fact, the numerical representation of mixing processes between a cloud and the surrounding air has been a key issue in model parameterizations for decades. To better study these mixing processes as well as their impacts on cloud microphysical properties, the paper aims to improve exploration strategies that can be implemented by a fleet of RPA. Here, we use a large-eddy simulation (LES) of shallow maritime cumulus clouds to design adaptive sampling strategies. An implementation of the RPA flight simulator within high-frequency LES outputs (every 5 s) allows tracking individual clouds. A rosette sampling strategy is used to explore clouds of different sizes that are static in time and space. The adaptive sampling carried out by these explorations is optimized using one or two RPA and with or without Gaussian process regression (GPR) mapping by comparing the results obtained with those of a reference simulation, in particular the total liquid water content (LWC) and the LWC distribution in a horizontal cross section. Also, a sensitivity test of length scale for GPR mapping is performed. The results of exploring a static cloud are then extended to a dynamic case of a cloud evolving with time to assess the application of this exploration strategy to study the evolution of cloud heterogeneities. While a single RPA coupled to GPR mapping remains insufficient to accurately reconstruct individual clouds, two RPA with GPR mapping adequately characterize cloud heterogeneities on scales small enough to quantify the variability of important parameters such as total LWC.

Mechanisms responsible for interdecadal variation of the thermodynamic component of East Asian summer monsoon moisture transport

AbstractIn this study, the East Asian summer (June–July–August) monsoon (EASM) atmospheric moisture transport variability under global warming are examined using ERA‐Interim reanalysis data from 1979 to 2019. The total EASM atmospheric moisture transport is decomposed into the thermodynamic (δTH) and dynamic (δMCD) components, which are related to specific humidity and wind velocity, respectively. Based on empirical orthogonal function (EOF) analysis, both the second and the fourth modes of δTH are linked to δMCD, indicating that δMCD can impact the moisture distribution and consequently influence δTH indirectly. Both the first (δTH_EOF1) and the third (δTH_EOF3) modes of δTH show considerable interdecadal changes. It is noted that their principal components exhibit significant increasing trends in recent decades. The response of EASM moisture transport to global warming is probably reflected in these two modes. δTH_EOF1 is associated with negative phases of the Interdecadal Pacific Oscillation (IPO)/Pacific Decadal Oscillation (PDO). This causes the western North Pacific subtropical high (WNPSH) to extend westward and the strengthening of Pacific trade winds. As a result, positive precipitable water anomalies dominate East Asia and δTH_EOF1 is characterized by anomalous southwesterly moisture transport along the East China Sea to southern Japan. δTH_EOF3 corresponds to anomalous moisture transport over the Indochina Peninsula and Japan. The precipitable water associated with δTH_EOF3 in general represents a meridional dipole. Anomalous southward wind induced by the eastward extension of the WNPSH is the main reason for positive (negative) precipitable water anomalies in southern (northern) East Asian. The anomalous circulation associated with the anomalous east–west sea surface temperature gradient over the Indian Ocean affects atmospheric moisture in southern East Asian and can dramatically impact δTH_EOF3.

EUREC<sup>4</sup>A's <i>Maria S. Merian</i> ship-based cloud and micro rain radar observations of clouds and precipitation

Abstract. As part of the EUREC4A field campaign, the research vessel Maria S. Merian probed an oceanic region between 6 to 13.8∘ N and 51 to 60∘ W for approximately 32 d. Trade wind cumulus clouds were sampled in the trade wind alley region east of Barbados as well as in the transition region between the trades and the intertropical convergence zone, where the ship crossed some mesoscale oceanic eddies. We collected continuous observations of cloud and precipitation profiles at unprecedented vertical resolution (7–10 m in the first 3000 m) and high temporal resolution (1–3 s) using a W-band radar and micro rain radar (MRR), installed on an active stabilization platform to reduce the impact of ship motions on the observations. The paper describes the ship motion correction algorithm applied to the Doppler observations to extract corrected hydrometeor vertical velocities and the algorithm created to filter interference patterns in the MRR observations. Radar reflectivity, mean Doppler velocity, spectral width and skewness for W-band and reflectivity, mean Doppler velocity, and rain rate for MRR are shown for a case study to demonstrate the potential of the high resolution adopted. As non-standard analysis, we also retrieved and provided liquid water path (LWP) from the 89 GHz passive channel available on the W-band radar system. All datasets and hourly and daily quicklooks are publically available, and DOIs can be found in the data availability section of this publication. Data can be accessed and basic variables can be plotted online via the intake catalog of the online book “How to EUREC4A”.

Near-Surface Atmospheric Behavior over Complex Tropical Topography in Puerto Rico Dominated by Seasonal Patterns Despite Frequent Environmental Changes

Abstract Understanding near-surface atmospheric behavior in the tropics is imperative given the role of tropical energy fluxes in Earth’s climate cycles, but this area is complicated by a land–atmosphere interaction that includes rugged topography, seasonal weather drivers, and frequent environmental disturbances. This study examines variation in near-surface atmospheric behaviors in northeastern Puerto Rico using a synthesis of data from lowland and montane locations under different land covers (forest, urban, and rural) during 2008–21, when a severe drought, large hurricanes (Irma and Maria), and the COVID-19 mobility-reducing lockdown occurred. Ceilometer, weather, air quality, radiosonde, and satellite data were analyzed for annual patterns and monthly time series of data and data correlations. The results showed a system that is strongly dominated by easterly trade winds transmitting regional oceanic patterns over terrain. Environmental disturbances affected land–atmosphere interaction for short time periods after events. Events that reduce the land signature (reducing greenness: e.g., drought and hurricanes, or reducing land pollution: e.g., COVID-19 lockdown) were evidenced to strengthen the transmission of the oceanic pattern. The most variation in near-surface atmospheric behavior was seen in the mountainous areas that were influenced by both factors: trade winds, and terrain-induced orographic lifting. As an exception to the rest of the near-surface atmospheric behavior, pollutants other than ozone did not correlate positively or negatively with stronger trade winds at all sites across the region. Instead, these pollutants were hypothesized to be more anthropogenically influenced. Once COVID-19 lockdown had persisted for 3 months, urban pollution decreased and cloud base may have increased.

Energy Dispersion of Westward Propagating Rossby Waves in Tropical Easterlies

Energy Dispersion of Westward Propagating Rossby Waves in Tropical Easterlies

Increased summer electric power demand in Beijing driven by preceding spring tropical North Atlantic warming

By using electric power data, observational station temperature data in Beijing, CN05.1 temperature data, ERA5 atmospheric reanalysis data, and ERSST.v3b sea surface temperature (SST) data, it is found that summer (July–August) electric power demand in Beijing is remarkably positively correlated with the previous spring (March–April) tropical North Atlantic (TNA) SST anomaly (SSTA). The possible physical mechanism of the TNA SSTA affecting summer electric power in Beijing is also revealed. When a positive SSTA occurs in the TNA during spring, anomalous easterlies prevail over the tropical central Pacific, which can persist to the following summer. Trade winds are thus enhanced over the northern Pacific, which favors a strengthening of upwelling cold water in the tropical central-eastern Pacific. As a result, a negative SSTA appears in the central-eastern Pacific in summer, which means a La Niña event is triggered by the previous TNA SSTA through the Bjerknes feedback. During the La Niña event, an anomalous anticyclonic circulation occupies the northwestern Pacific. The southerly anomalies at the western edge of this anomalous anticyclone strengthen the transportation of warm and humid airflow from the low latitudes to North China, where Beijing is located, causing higher summer temperatures and increased electricity usage for air conditioning, and vice versa. The results of this study might provide a new scientific basis and clues for the seasonal prediction of summer electric power demand in Beijing.摘要本文利用北京市电力负荷资料, 北京市站点观测温度资料, CN05.1温度资料, ERA5大气再分析资料及ERSST v3b海表温度资料, 发现3–4月副热带北大西洋海温异常和北京市夏季电力呈很好的正相关关系, 并揭示了副热带北大西洋海温异常影响北京市夏季电力的可能物理机制. 春季副热带北大西洋海温异常偏暖, 热带中太平洋出现东风异常并持续至夏季, 太平洋信风增强, 热带中东太平洋冷水上翻增强, 通过Bjerkness正反馈机制激发了La Niña事件. La Niña事件时, 西北太平洋反气旋环流异常, 将低纬度暖湿气流输送至北京地区, 引起北京市夏季温度增高, 电力负荷需求增加. 反之亦然. 研究结果可为北京市夏季电力负荷需求的季节预测提供新的科学依据和线索.

Features of the formation of the Central and East Pacific La Niña types

In this paper the dataset of global ocean chlorophyll «a» (Chl a) concentration from the GlobColour project over the equatorial Pacific during the La Niña events from 1998 to 2018 is analyzed. GlobColour includes satellite sensors such as SeaWiFS, MODIS, MERIS and others. The study of changes in chlorophyll «a» concentration is carried out with an analysis of sea temperature and current distributions on the surface and over the ocean depth taken from the NCEP GODAS reanalysis from 1981 to 2018. Additionally the trade wind indices from 1979 to 2018 are used. The purpose of the work is to study the mechanisms of formation of two La Niña types, leading to the occurrence of different climatic anomalies in different regions of our planet. It is found that at the initial stage of the Central Pacific La Niña type origin the ocean chlorophyll «a» concentration over the center equatorial Pacific increases in six to eight times (from 0.1 mg/m3 to 0.8 mg/m3) and the thermocline depth in this area decreases to 50 m indicating the intensification of the central equatorial upwelling. During the East Pacific La Nina type the central equatorial upwelling is not formed and negative sea surface temperature anomalies are formed by increasing of the Peruvian upwelling supported intensification trade winds on the East Pacific equatorial sector. All obtained results are confirmed by a 95% statistically significant by Student's test. Thus, the work is demonstrated significant differences in the features of the two La Niña types formation at their initial stage of origin.

Analysis of meteorological variables interaction associated with the environment of formation of Amazonian squall lines.

The relationships among humidity, air temperature, wind, and vertical velocity with formation and propagation of Amazonian squall lines (ASL) is analyzed in this study. One year of data (2005) is verified by counting ASL cases according to their classification (propagated and non-propagated) to understand more clearly how the variation of these variables over this year influences their environment of formation. The results show an increase in humidity on days with ASL, with the highest occurrence during the wettest months. Furthermore, system propagation toward the interior of continent seems to be strongly related to the moisture content that reaches the coast, through the winds that blow from the ocean from both by the Northeast Trade Winds, of the North Atlantic Subtropical High, and by the Southeast Trade Winds, of the South Atlantic Subtropical High. Higher moisture content from the sea corresponds to a higher wind intensity toward the coast. A relationship between continent/ocean temperature gradient and the ASL amount and types formed is also demonstrated. Such information is extremely relevant because of the great importance of these systems in the extreme north and northeast regions of Brazil, particularly at the Amazon, given the difficulty of predicting them due to their complexity.

Atmospheric Flow at Alcantara Launch Center

The Alcantara Launch Center (ALC) is the main Brazilian access to space. It is positioned over a complex terrain, and it has some important buildings for assembling, integration and launching activities, such as the Mobile Integration Tower. Being in a region of prevalent trade winds, the flow interaction between the complex terrain and the buildings can affect the safety of operations on the platform, and the dispersion of toxic gases emitted during the launching. The main objective of this work was to study the influence of topography and buildings on the atmospheric flow of ALC using computational fluid dynamics (CFD) techniques. Three geometries were considered: simplified terrain (case 1), smooth complex terrain (case 2), and roughness complex terrain (case 3). The flow conditions over ALC were simulated using the ANSYS Fluent 19.0 CFD commercial code. The numerical simulations used a realizable ?-? to model turbulence effects and the results presented a good agreement with the in-situ field measurements for the most complex geometry (case 3). The topography clearly influences the flow pattern at ALC, with the cliff influence over the wind being the major cause for establishing the flow patterns.

Evidence for anthropogenic, climatic and oceanographic variability off southwestern Morocco during the last three millennia

In order to obtain a better knowledge of oceanic changes in the Canary Upwelling region during the Late Holocene, marine surface samples and two sediment cores retrieved off southwestern Morocco, GeoB8601–3 and GeoB4223–1, were investigated for organic-walled dinoflagellate cysts (dinocysts). The results were compared with pollen, microcharcoal particles, geochemical records, stable hydrogen and carbon isotope composition (δ 2 H and δ 13 C) of plant-waxes of the same material. The dinocyst results indicate active upwelling prior to 750 BCE and a longer upwelling season between 750 BCE and 950 CE, which is attributed to increased northeast trade winds. After 950 CE, a marked increase of Lingulodinium machaerophorum and Gymnodinium species indicates high fluvial input probably due to a combination of climate (possibly negative NAO) and anthropogenic (terrestrial erosion related to Early Arab conquest) impacts. • We present a new compilation of modern dinocyst distribution off southwestern Morocco. • We investigate Late Holocene dinocyst records from two marine sediment cores. • We employ a multiproxy approach with pollen, microcharcoal and geochemical records. • An interplay of climate and anthropogenic controls were demonstrated.

Different Influencing Mechanisms of Two ENSO Types on the Interannual Variation in Diurnal SST over the Niño-3 and Niño-4 Regions

AbstractIn this paper, the different effects of the eastern equatorial Pacific (EP) and central equatorial Pacific (CP) Ocean El Niño–Southern Oscillation (ENSO) events on interannual variation in the diurnal sea surface temperature (SST) are explored in both the Niño-3 and Niño-4 regions. In the Niño-3 region, the diurnal SST anomaly (DSSTA) is negative during both EP and CP El Niño events and becomes positive during both EP and CP La Niña events. However, the DSSTA in the Niño-4 region is positive in El Niño years and negative in La Niña years, which is opposite to that in the Niño-3 region. Further analysis indicates that the incident shortwave radiation (SWR), wind stress (WS), and upward latent heat flux (LHF) are the main factors causing the different interannual variations in the DSST. In the Niño-3 region, decreased SWR and increased LHF lead to a negative DSSTA in EP El Niño years, and enhanced WS and increased LHF cause a negative DSSTA in CP El Niño years. Conversely, in that same region, increased SWR and decreased LHF lead to a positive DSSTA in EP La Niña years, and reduced WS and decreased LHF cause a positive DSSTA in CP La Niña years. In the Niño-4 region, the reduced trade wind plays a key role in producing the positive DSSTA, whereas the decreased SWR has an opposite effect that reduces the range of the DSSTA during both EP and CP El Niño events, and conversely the enhanced trade wind plays a key role in producing the negative DSSTA, whereas the increased SWR has an opposite effect that increases the range of the DSSTA during both EP and CP La Niña events.

Satellite-Derived Aerosol–Cloud Relationships Under Anthropogenic Polluted Conditions of Arabian Sea

Uncertainty associated with estimating the impact of anthropogenic aerosols on clouds is hindering accurate projections of future climate. Here, we evaluate the effect of aerosols on clouds under anthropogenic polluted conditions and relatively maritime conditions, over the Arabian Sea (AS), under the influence of the same large-scale meteorology and spatiotemporal domains. The relationship between diurnal mean cloud macrophysical properties, namely, cloud fraction (CF) and cloud top temperature (CTT) from geostationary satellite (INSAT-3D), and aerosol properties, from Moderate Resolution Imaging Spectroradiometer (MODIS), is examined for the winter months of 2018. During winter, trade winds transport large quantities of continental aerosols over to the AS, where the semipermanent field of stratocumulus cloud layers exists. We observed distinctively different cloud macrophysical properties over polluted conditions compared to maritime conditions. The strengths of aerosol–cloud interaction on CF and CTT are, respectively, 0.3 and −0.02 for polluted conditions and are 0.1 and −0.005, respectively, for maritime conditions, with an increase in the aerosol index from 0.0 to 0.6. Absorbing aerosol radiative effects at elevated layers over polluted conditions majorly drive the observed changes in cloud properties. Further analysis of Cloud-Aerosol LiDAR and Infrared Pathfinder Satellite Observations (CALIPSO) profiles illustrates the bimodal structure of cloud occurrence over polluted conditions. Elevated absorbing aerosol layers above stratus clouds enhance low-level cloud cover. Besides, warming due to elevated absorbing aerosols reduces intermingled cumulus cloud layers and, at the same time, enhances the development of growing cloud layers above elevated pollution layers. The observed changes in cloud macrophysical properties in relation to the mutual position of aerosol and cloud layers suggest a more complicated cloud regime-dependent process over this region.