Strengthening Of Winds Research Articles

Modeling the advective supply of Calanus finmarchicus to Stellwagen Bank as an indicator of sand lance foraging habitat, and the climate vulnerability of a National Marine Sanctuary

The northern sand lance (Ammodytes dubius), a key species in the food web supporting the Stellwagen Bank National Marine Sanctuary (SBNMS), feeds primarily on the lipid-rich copepod Calanus finmarchicus. Climate change poses a significant threat to this dynamic, as C. finmarchicus populations are at the southern edge of their subarctic distribution and are vulnerable to warming waters and changing oceanographic conditions. Declines in the advective supply of C. finmarchicus to Stellwagen Bank could adversely affect sand lance populations and, consequently, the ecological and economic resources that depend on them. To quantify the connectivity between SBNMS and potential sources of C. finmarchicus, we used the Finite-Volume Community Ocean Model (FVCOM) coupled with Lagrangian particle tracking over the years 1978 to 2016. Numerical experiments revealed that Stellwagen Bank is highly connected to upstream areas in the Maine Coastal Current (MCC), where existing time series monitoring stations observe C. finmarchicus populations. The connectivity exhibited strong seasonal patterns, with peak connectivity occurring during spring and early summer, aligning with the sand lance feeding period on C. finmarchicus. We found significant interannual variability, influenced by changes in the strength of the MCC and circulation patterns in the western Gulf of Maine. Years with stronger MCC flow showed higher connectivity and a greater potential supply of C. finmarchicus particles to Stellwagen Bank. Conversely, periods of reduced flow corresponded with decreased connectivity, potentially limiting the availability of C. finmarchicus to sand lance populations. Meanwhile, observations from drifters and buoys since 2001 have documented decreases in MCC current speed which has been linked to a climate driven strengthening of southwesterly winds. These findings underscore the importance of pelagic habitat connectivity in assessing the climate vulnerability of marine protected areas (MPAs) like SBNMS. Furthermore, monitoring C. finmarchicus populations at upstream time series stations can provide information on downstream foraging habitat in MPAs, and potentially in other vulnerable areas of ecological and socioeconomic interest. By incorporating these indicators of connectivity and upstream C. finmarchicus population abundance into decision support tools, Sanctuary managers and stakeholders can make informed decisions to mitigate potential climate impacts.

Dominant inflation of the Arctic Ocean’s Beaufort Gyre in a warming climate

The Arctic Ocean’s Beaufort Gyre, the largest Arctic freshwater reservoir, plays a crucial role for climate and marine ecosystems. Understanding how it changes in a warming climate is therefore essential. Here, using high-resolution simulations and Coupled Model Intercomparison Project phase 6 data, we find that the Beaufort Gyre will increasingly accumulate freshwater, elevate sea level, and spin up its circulation as the climate warms. These changes, collectively referred to as inflation, are more pronounced in the Beaufort Gyre region than in other Arctic areas, amplifying the spatial asymmetry of the Arctic Ocean. The inflation is driven by increased surface freshwater fluxes and intensified surface stress from wind strengthening and sea ice decline. Current climate models tend to underestimate this inflation, which could be alleviated by high-resolution ocean models and improved atmospheric circulation simulations. The inflation of the Beaufort Gyre underscores its growing importance in a warming climate.

Amplification of Northern Hemisphere winter stationary waves in a warming world

This study leverages the Global/Regional Integrated Model system (GRIMs) version 4.0 climate model to examine the mechanisms behind the recent intensification of winter stationary waves over western North America. Prescribed sea surface temperature warming forces a strengthening of westerly winds, amplifying the ridge that characterizes the stationary waves in western North America. The streamfunction budget analysis reveals relative vorticity advection is mainly associated with this process. We further show that ocean warming is the primary driver of changes in westerly winds and stationary waves in the Northern Hemisphere. Sea ice losses exert a considerable effect through a different mechanism, complementing the dominant influence of ocean warming on these atmospheric changes. Our results thus reveal the crucial role tropical oceans play in modulating global warming’s effect on the stationary waves in the Northern Hemisphere and add a more quantitative perspective to the previously reported influence of Arctic amplification.

Formation Mechanisms of the Decadal Indian Ocean Dipole Driven by Remote Forcing from the Tropical Pacific

Abstract On decadal time scales, a zonal SST dipole dominates the tropical Indian Ocean in boreal late summer and fall, called the decadal Indian Ocean dipole (D-IOD). The D-IOD has a spatial pattern different from the traditional interannual IOD, with its eastern pole located off Java, rather than the whole Sumatra–Java coasts as the latter. Here, we show that the D-IOD is generated by both the remote tropical Pacific decadal variability (TPDV) forcing and the decadal modulation of interannual IODs, but with its distinctive spatial pattern and seasonality mainly shaped by the former. In August–September (AS), due to the seasonal strengthening of trade winds, the descending branch of TPDV-induced Walker circulation moves westward into the eastern Indian Ocean relative to June–July, which stimulates equatorial easterly anomalies and oceanic upwelling Kelvin waves, causing subsurface cooling off Java. The subsurface cooling just occurs within the time window of climatological coastal upwelling so that subsurface cold anomalies are brought into the surface by mean upwelling and further transported offshore by mean flows, forming the D-IOD eastern pole. The subsurface cooling is only generated near Java but not Sumatra, because the former is closer to the exit of the Indonesian Throughflow (ITF). Weakened ITF during positive TPDV inhibits the growth of subsurface warming off Java prior to the establishment of AS equatorial easterly anomalies, whereas this ITF effect is not observed off Sumatra. Moreover, warming of the D-IOD western pole might be associated with off-equatorial Rossby waves induced by TPDV-related wind stress curls. Significance Statement The decadal Indian Ocean dipole (D-IOD) is one of the leading decadal modes of the tropical Indian Ocean SST variations. Its formation mechanisms, especially those related to its spatiotemporal characteristics, are not well understood. Based on observations and reanalysis, we show that the tropical Pacific decadal variability (TPDV) mainly accounts for the distinctive spatial pattern and seasonality of the D-IOD via the seasonal migration of the anomalous Walker circulation and ensuing oceanic subsurface dynamics. Our results highlight that the TPDV is an important source of D-IOD’s predictability, and it might be beneficial for operational decadal predictions for the tropical Indian Ocean.

An Observational Case Study of a Radiation Fog Event

A micrometeorological fog experiment was carried out in Budapest, Hungary during the winter half year of 2020–2021. The field observation involved (i) standard meteorological and radiosonde measurements; (ii) surface radiation balance and energy budget components, and (iii) ceilometer measurements. 23 fog events occurred during the whole campaign. Foggy events were categorized based on two different methods suggested by Tardif and Rasmussen (2007) and Lin et al. (2022). Using the Present Weather Detector and Visibility sensor (PWD12), duration of foggy periods are approximately shorter (~ 9%) compared to ceilometer measurements. The categorization of fog based on two different methods suggests that duration of radiation fogs is lower compared to that of cloud base lowering (CBL) fogs. The results of analysis of observed data about the longest fog event suggest that (i) it was a radiation fog that developed from the surface upwards with condition of a near neutral temperature profile. Near the surface the turbulent kinetic energy and turbulent momentum fluxes remained smaller than 0.4 m2 s–2 and 0.06 kg m–1 s–2, respectively. In the surface layer the vertical profile of the sensible heat flux was near constant (it changes with height ~ 10%), and during the evolution of the fog, its maximum value was smaller than 25 W m–2, (ii) the dissipation of the fog occurred due to increase of turbulence, (iii) longwave energy budget was close to zero during fog, and a significant increase of virtual potential temperature with height was observed before fog onset. The complete dataset gives an opportunity to quantify local effects, such as tracking the effect of strengthening of wind for modification of stability, surface layer profiles and visibility. Fog formation, development and dissipation are quantified based on the micrometeorological observations performed in suburb area of Budapest, providing a processing algorithm for investigating various fog events for synoptic analysis and for optimization of numerical model parameterizations.

Long‐Term Variability and Tendencies in Mesosphere and Lower Thermosphere Winds From Meteor Radar Observations Over Esrange (67.9°N, 21.1°E)

AbstractLong‐term variabilities of monthly zonal (U) and meridional winds (V) in northern polar mesosphere and lower thermosphere (MLT, ∼80–100 km) are investigated using meteor radar observations during 1999–2022 over Esrange (67.9°N, 21.1°E). The summer (June‐August) mean zonal winds are characterized by westward flow up to ∼88–90 km and eastward flow above this height. The summer mean meridional winds are equatorward with strong jet at ∼85–90 km and it weakens above this height. The U and V exhibit strong interannual variability that varies with altitude and month or season. The responses of U and V anomalies (from 1999 to 2003) to solar cycle (SC), Quasi Biennial Oscillation at 10 and 30 hPa, El Niño‐Southern Oscillation, North Atlantic Oscillation, ozone (O3) and carbon dioxide (CO2) are analyzed using multiple linear regression. From analysis, significant regions of correlations between MLT winds and above potential drivers vary with altitude and month. The positive responses of U and V to SC (up to 15 m/s/100 sfu) indicates the strengthening of eastward winds in mid‐late winter, and poleward winds in late autumn and early winter. The O3 likely intensifies the eastward and poleward winds (∼100 m/s/ppmv) in winter and early spring. The CO2 significantly influence the eastward flow in late winter and summer (above ∼90–95 km) and strengthen the meridional circulation. The significant positive trend in U peaks in summer, late autumn and early winter (∼0.6 m/s/year), the negative trend in V is more prominent in summer above ∼90–95 km.

A North–South Dipole Response of the South Atlantic Convergence Zone During the Mid‐Holocene

AbstractThe South Atlantic Convergence Zone (SACZ) profoundly modulates precipitation from central to southeastern Brazil in the present‐day climate. However, the understanding of its long‐term behavior responding to various climate forcings remains limited. Here, we use an isotope‐enabled atmospheric general circulation model (ECHAM4.6) to examine the precipitation response of the SACZ during the mid‐Holocene about six thousand years ago. The model simulates a northward intensification of the SACZ in the mid‐Holocene, resulting in a dipole anomaly pattern relative to today's climate. The mid‐Holocene precipitation increased along the northern margin of the SACZ due to the strengthening of easterly winds across the tropical Atlantic, while an eastward deflection of the South American low‐level jet reduced moisture transport to southern Brazil, resulting in reduced precipitation along the southern margins of the SACZ. The north–south dipole response in precipitation is consistent with the mid‐Holocene hydroclimate change observed in proxy records from the region.

Comprehensive characterization of Marine Heatwaves in a coastal Northern Humboldt Current System regional model over recent decades

In this study, a high-resolution hydrodynamic model simulation was used to analyze the three-dimensional characteristics of marine heatwaves (MHWs) in the coastal region of the Northern Humboldt Current System (NHCS) over the period 2000–2019. Three distinct vertical layers were identified. The near-surface layer, extending down to 75 m depth, is identified as the region where both the maximum MHW intensity and cumulative intensity are found, predominantly concentrated along the thermocline depth. The intermediate layer, spanning from 75 to 125 m depth, exhibited the longest MHW durations and the lowest MHW frequencies. MHWs in this layer tend to be of moderate intensity and are often associated with ENSO variability. In contrast, the deep layer, from 125 to 250 m depth, was characterized by short-lived MHWs of low intensity. These MHWs exert a lesser thermal impact on the region. To understand the drivers of MHWs, a composite analysis was performed. The results highlighted the significant role exerted by wind-driven anomalies in the life cycle of MHWs. It was found that the combined effect of a sluggish coastal upwelling circulation and suppressed oceanic heat loss, as a result of weakened winds, preceded the MHW formation. Conversely, the strengthening of winds, which enhanced net heat loss, primarily driven by latent heat flux anomalies, and an enhancement of the cooling effect due to the recovery of the coastal upwelling circulation, are key processes in ending a typical MHW event in the coastal region. These findings expand our understanding of the MHWs and their associated potential drivers and help to reveal which regions are most susceptible to extreme climate events in one of the most productive marine ecosystems worldwide.

The westerly winds control the zonal migration of rainy season over the Tibetan Plateau

Precipitation over the Tibetan Plateau is modulated by both the South Asian summer monsoon and the mid-latitude westerly winds. Using observations and numerical simulations, this study highlights the out-of-phase relationships between the mid-latitude westerly wind speeds and the west-east migration of Tibetan Plateau rainy season. When the westerly jet shifts northward before July, the weakening of westerly winds over the Tibetan Plateau leads to a westward shift of low-level warm air center and a westward extension of moist air convergence. Consequently, rainy season advances westward. Conversely, the southward shift of westerly jet after August leads to a strengthening of westerly winds and an eastward retreat of rainy season. Numerical simulations confirm the dominant role of mid-latitude westerly winds on the rain belt migration over the Tibetan Plateau, and further indicate that the timing of the westward extension of rain belt is determined by the weakening of mid-latitude westerly winds.

Origin and Evolution of Synoptic-Scale Vortices Initiated at Low Level Downwind of the Hoggar Mountains

Abstract Numerous low-level vortices are initiated downwind of the Hoggar Mountains and progress toward the Atlantic coast on the northern path of African easterly waves (AEWs). These vortices occur mostly in July and August and more specifically when the northern position of the Saharan heat low (SHL) generates stronger and vertically expanded easterly winds over the Hoggar Mountains. At synoptic time scales, a composite analysis reveals that vortex initiation and westward motion are also statistically triggered by a reinforcement of these easterly winds by a wide and persistent high pressure anomaly developing around the Strait of Gibraltar and by a weak wave trough approaching from the east. The vortices are generated in the lee of the Hoggar, about 1000 km west of this approaching trough, and intensify rapidly. The evolution of the vortex perturbation is afterward comparable with the known evolution of the AEWs of the northern path and suggest a growth due to dry barotropic and baroclinic processes induced in particular by the strong cyclonic shear between the reinforced easterly winds and the monsoon flow. These results show that vortex genesis promoted by changes in orographic forcing due to the strengthening of easterly winds over the Hoggar Mountains is a source of intensification of the northern path of AEWs in July and August. These results also provide a possible mechanism to explain the role of the SHL and of particular midlatitude intraseasonal disturbances on the intensity of these waves.

О МЕХАНИЗМЕ РЕЗКОГО ПОНИЖЕНИЯ ТЕМПЕРАТУРЫ ПОВЕРХНОСТИ В СЕВЕРО-ЗАПАДНОЙ ЧАСТИ ЧЕРНОГО МОРЯ И У ПОБЕРЕЖЬЯ КРЫМА

An analysis of high-resolution satellite data on sea surface temperature (SST) and surface wind for 2008-2021 confirmed that the areas of a dramatic SST drop exceeding several degrees per day regularly occur in the northwestern Black Sea and off the western coast of Crimea. These areas are located not only in coastal upwelling zones. Extensive areas of this type are found in the open water areas in the northwestern part of the sea and in the vicinity of the western large-scale cyclonic gyre. A reason for the formation of such areas during the period of the stable vertical thermal stratification in the upper layer is the strengthening of wind in the atmospheric surface layer and the intensification of cyclonic vorticity. This leads to the generation of upward motions, additional turbulent mixing in the upper sea layer, and, as a consequence, the SST drop within a few days after the passage of the cyclone over the sea. This mechanism is especially effective in the case of slowly moving cyclones in the presence of a blocking or a high-pressure ridge northeast of the Black Sea region.

Uncertain future of sustainable fisheries environment in eastern boundary upwelling zones under climate change

Upwelling along ocean eastern boundaries is expected to intensify due to coastal wind strengthening driven by increasing land-sea contrast according to the Bakun hypothesis. Here, the latest high-resolution climate simulations that exhibit drastic improvements of upwelling processes reveal far more complex future upwelling changes. The Southern Hemisphere upwelling systems show a future strengthening in coastal winds with a rapid coastal warming, whereas the Northern Hemisphere coastal winds show a decrease with a comparable warming trend. The Bakun mechanism cannot explain these changes. Heat budget analysis indicates that temperature change in the upwelling region is not simply controlled by vertical Ekman upwelling, but also influenced by horizontal heat advection driven by strong near-coast wind stress curl that is neglected in the Bakun hypothesis and poorly represented by the low-resolution models in the Coupled Model Intercomparison Project. The high-resolution climate simulations also reveal a strong spatial variation in future upwelling changes, which is missing in the low-resolution simulations.

Orbitally and galactic cosmic forced abrupt climate events during the last glacial period

Various abrupt climate events have been reported during the last glacial period, but their regional expressions and causes remain complex and not fully understood largely due to lack of high-resolution paleoclimate records. In this study, a high-resolution loess sequence is presented from North China which is significantly influenced by the East Asian Summer Monsoon, and its multiple proxies reveal two strong, abrupt cooling-drying events occurring at 48 ka and ∼42 ka. The 48 ka event corresponds to the fifth Heinrich (H5) event that was characterized by catastrophic iceberg discharges into the subpolar North Atlantic Ocean. Our loess and model results suggest that the 48 ka event could result from the unique and extreme orbital configuration at 48 ka, characterized by the smallest latitudinal summer insolation gradient over the last glacial period. This orbital configuration led to a cooling-drying in the low and mid-latitudes but a warming in high latitudes. The ∼42 ka event corresponds to a catastrophic environmental crisis discovered on the Eurasian and Australian continents. It also corresponds to a major reversal of the Earth's magnetic poles, i.e., the Laschamps Excursion. The cosmic ray increase due to this Excursion could affect the pedogenesis and dust deposition of the loess sequence via cloud increase, regional cooling, aerosol increase and local wind strengthening. This study is a clear demonstration that both extreme orbital conditions and the change of the Earth's magnetic field could cause abrupt climate and environmental changes.

Gone with the wind – Wind speed affects prey accessibility for a High Arctic zooplanktivorous seabird, the little auk Alle alle

Foraging ecology of chick rearing seabirds is affected mainly by the food availability on feeding grounds, but it can be also modulated by environmental conditions during the foraging trip, in that wind force. Considering predicted strengthening of surface winds over the Arctic Ocean, this factor may have a growing impact on the foraging performance of Arctic seabirds. Here, we studied how wind speed could affect prey accessibility for the High Arctic zooplanktivorous seabird, the little auk Alle alle breeding in Svalbard in 2015–2019. First, we estimated availability of its preferred prey, a cold water copepod Calanus glacialis, based on wider-scale mesozooplankton biomass model and environmental conditions. Then we estimated prey accessibility by including wind speed, the factor affecting the flapping flight performance of little auks commuting from/to the colony. Finally, we compared reproductive performance of the little auks (chick diet, growth rate and survival and duration of foraging flights of adults) between the studied years differing in wind and food availability conditions. We found that wind speed could affect significantly food accessibility for a zooplanktivorous seabird. Despite high spatial and temporal variability in prey availability and accessibility in shelf waters of SW Spitsbergen, interannual differences in duration of foraging flights and chick growth rate, little auks were able to sustain high breeding success confirming their capacity to buffer suboptimal foraging conditions. Our multidisciplinary work, combining multi-year remote sensing of oceanographic conditions, zooplankton availability and accessibility modelling, little auks diet composition and chick growth and survival emphasizes the importance of including wind conditions in the studies of foraging ecology of seabirds.

Climate variability along the margin of the southern African monsoon region at the end of the African Humid Period

Evidence for climate variability in the southern African monsoon region (SAMR) is limited by a spatially and temporally discontinuous palaeoclimatic dataset. We describe a 6680 year long, largely sub-decadal resolution δ15N record from a rock hyrax midden from southeastern Africa. The results provide a detailed reconstruction of regional hydroclimates since the beginning of the mid-Holocene. A long-term – albeit subtle – increase in humidity consistent with precessional forcing is observed, but the record is dominated by a strong ∼1750-yr cycle, a signal that is shared with other SAMR records. Considered in their regional context, these data suggest that changes coincident with the termination of the African Humid Period at ∼5500 cal BP do not express the abrupt transition observed in some records from the northern African tropics. Rather they indicate gradual changes, as observed at peri-equatorial sites. Notably, however, eastern and western subregions of the SAMR experience a rapid phase shift beginning ∼5500 cal BP, with initially in-phase hydroclimate anomalies transitioning to the establishment of a strong east-west dipole. This likely reflects a coeval strengthening of the Southeast Atlantic trade winds and decreased atmospheric pressure in southeast Africa, factors associated with increasing (decreasing) austral (boreal) summer insolation. The results highlight the distinct nature of southern African responses across this key period of African climate history.

Future trends of arctic surface wind speeds and their relationship with sea ice in CMIP5 climate model simulations

Recent climate change in the Arctic has been rapid and dramatic, leading to numerous physical and societal consequences. Many studies have investigated these ongoing and projected future changes across a range of climatic variables, but surprisingly little attention has been paid to wind speed, despite its known importance for sea ice motion, ocean wave heights, and coastal erosion. Here we analyzed future trends in Arctic surface wind speed and its relationship with sea ice cover among CMIP5 global climate models. There is a strong anticorrelation between climatological sea ice concentration and wind speed in the early 21st-century reference climate, and the vast majority of models simulate widespread future strengthening of surface winds over the Arctic Ocean (annual multi-model mean trend of up to 0.8 m s−1 or 13%). Nearly all models produce an inverse relationship between projected changes in sea ice cover and wind speed, such that grid cells with virtually total ice loss almost always experience stronger winds. Consistent with the largest regional ice losses during autumn and winter, the greatest increases in future wind speeds are expected during these two seasons, with localized strengthening up to 23%. As in other studies, stronger surface winds cannot be attributed to tighter pressure gradients but rather to some combination of weakened atmospheric stability and reduced surface roughness as the surface warms and melts. The intermodel spread of wind speed changes, as expressed by the two most contrasting model results, appears to stem from differences in the treatment of surface roughness.

Maintenance and development of the Ural high and its contribution to severe cold wave activities in winter 2020/21

Two successive severe cold waves invaded eastern China from the end of 2020 to early 2021, leading to an extensive, severe, and persistent drop in temperature. The paper investigates the features and formation mechanisms of the two cold waves. The main results are as follows: (1) An anticlockwise turning of the transverse trough was observed in both cold waves. However, a broad ridge was maintained over the Ural area from mid-December 2020 till mid-January 2021. No breakdown or discontinuous westward shift of the blocking high was observed, which is different from typical cold waves in eastern Asia. (2) The maintenance and strengthening of northerly winds in front of the Ural high led to an increase in baroclinicity in-situ. In the downstream region, the gradient of the geopotential height contour in the south of the transverse trough rapidly increased and the advection of cold temperature consistently enhanced and advanced southwards. This in turn caused the intensification and southward expansion of the Siberian high. (3) Energy propagation of the quasi-stationary wave was a reason for the development and persistence of the Ural blocking. Prior to the occurrence of the two cold waves, the energy of the low-frequency stationary wave originating from near 0°E (or even to the west) propagated eastwards, which helped the Ural ridge intensify and maintain. Meanwhile, it also contributed to the development of the trough downstream of the ridge and resulted in the anticlockwise turning of the transverse trough, providing a favorable condition for the southward outbreak of cold air.摘要2020年底至2021年初, 连续两次强寒潮入侵中国东部地区, 导致大范围强降温. 本文研究这两次寒潮的特征和形成机理. 主要结果如下: 从2020年12月中旬到2021年1月中旬, 乌拉尔山地区维持一宽阔的高压脊. 脊前北风的维持和加强导致局地斜压性增加, 导致下游横槽槽底等高线梯度加大, 冷平流加强, 西伯利亚高压加强和向南扩张. 准定常波能量传播是乌拉尔山阻塞发展和持续的主要原因. [Display omitted]

El Niño–Southern Oscillation signal in a new East Antarctic ice core, Mount Brown South

Abstract. Paleoclimate archives, such as high-resolution ice core records, provide a means to investigate past climate variability. Until recently, the Law Dome (Dome Summit South site) ice core record remained one of few millennial-length high-resolution coastal records in East Antarctica. A new ice core drilled in 2017/2018 at Mount Brown South, approximately 1000 km west of Law Dome, provides an additional high-resolution record that will likely span the last millennium in the Indian Ocean sector of East Antarctica. Here, we compare snow accumulation rates and sea salt concentrations in the upper portion (∼ 20 m) of three Mount Brown South ice cores and an updated Law Dome record over the period 1975–2016. Annual sea salt concentrations from the Mount Brown South site record preserve a stronger signal for the El Niño–Southern Oscillation (ENSO; austral winter and spring, r = 0.533, p < 0.001, Multivariate El Niño Index) compared to a previously defined Law Dome record of summer sea salt concentrations (November–February, r = 0.398, p = 0.010, Southern Oscillation Index). The Mount Brown South site record and Law Dome record preserve inverse signals for the ENSO, possibly due to longitudinal variability in meridional transport in the southern Indian Ocean, although further analysis is needed to confirm this. We suggest that ENSO-related sea surface temperature anomalies in the equatorial Pacific drive atmospheric teleconnections in the southern mid-latitudes. These anomalies are associated with a weakening (strengthening) of regional westerly winds to the north of Mount Brown South that correspond to years of low (high) sea salt deposition at Mount Brown South during La Niña (El Niño) events. The extended Mount Brown South annual sea salt record (when complete) may offer a new proxy record for reconstructions of the ENSO over the recent millennium, along with improved understanding of regional atmospheric variability in the southern Indian Ocean, in addition to that derived from Law Dome.

Spatial and temporal dynamics of the hydrology at Salinas Bay, Costa Rica, Eastern Tropical Pacific

Introduction: Salinas Bay is located in the warm pool of the Eastern Tropical Pacific (ETP), characterized by warm, shallow surface waters, a strong and shallow thermocline, and an important biological diversity. The primary productivity of the region is influenced by the coastal upwelling, which occurs during the boreal winter as a result of the strengthening of trade winds.
 Objective: To study the spatial and temporal dynamics of physical and chemical parameters at seven hydrographic stations in Salinas Bay, Costa Rica, through the analysis of CTD data, and relate the warm and cold events to the regional atmospheric conditions present when measuring the data.
 Methods: Seven hydrographic stations, sampled at Salinas Bay between August 2008 and December 2014, were selected. The variables processed for analysis are temperature, density, salinity, oxygen, chl-a and turbidity. Once the data was processed, 42 Hovmöller kind diagrams were plotted.
 Results: All variables, except turbidity, presented a seasonal periodicity associated with the upwelling. In general, colder and denser waters, higher salinity and chl-a concentrations and lower dissolved oxygen values were observed during the dry season, when the upwelling was active. Whereas, during the rainy season water masses were warmer and less dense, salinity and chl-a concentrations decreased and dissolved oxygen values tended to increase.
 Conclusions: The spatial and temporal dynamics of the hydrology in Salinas Bay was influenced by the coastal upwelling events. The region also presented an interannual variability associated with ENSO. Seasonal and interannual variability can counteract their effects on the oceanographic parameters when they coincide temporally.

Thermodynamic structure of monsoon boundary layer over the west coast of India

The study investigates thermodynamic structure of the atmospheric boundary layer (ABL) over the west coast of India during the southwest monsoon season. Radiosonde profiles at 00 UTC (0530 IST) are utilised for three stations, namely Thiruvananthapuram (TVM), Mangalore (MNG) and Mumbai (MUM) to represent south, central and north parts of the west coast, respectively. The high vertical resolution radiosonde data were collected from India Meteorological Department (IMD) for the period 1st May to 31st October 2018. Variations in the thermodynamic parameters associated with the monsoon and active and weak surges are examined. The active and weak monsoon conditions are identified using the values of OLR (outgoing longwave radiation) and rainfall in the respective stations. The study delineates interesting dynamic and thermodynamic features over the region. The thermodynamic parameters possess remarkable variations associated with the approach of the monsoon surges. TVM is characterised by absolutely stable or conditionally neutral (conditionally unstable) layer above a shallow conditionally unstable layer over the ground during the active (weak) monsoon situations; however, over MNG and MUM, ABL is conditionally unstable during both active and weak situations. Stable atmosphere is expected to cause stratiform clouds under favourable dynamic factors, whereas unstable atmosphere can aid vertical development of clouds and this can be attributed to the vertical shear of zonal wind. Zonal wind has a sharp increase from the ground to above ABL (~ 1200 m) in TVM; however, it is in the lower levels of ABL over MNG and MUM. In MUM, strong zonal wind is observed during the active (>20 m s−1) and weak (>12 m s−1) situations that causes intense mixing and maximum ABL height. The enhanced monsoon activity in MUM (MNG) is mainly associated with the active phase of the monsoon intraseasonal oscillation (active phase of the monsoon intraseasonal oscillation and strengthening of low level zonal wind), whereas in TVM it is mainly associated with the strengthening of low level zonal wind. The ABL heights are elevated during weak monsoon conditions due to convective turbulence added to the mechanical turbulence associated with the strong wind during the season.