Coastal Stations Research Articles

C-band dual-polarization Doppler weather radar at Thumba (8.537°N, 76.865°E): initial results and validation

Recently, a C-band dual-polarization Doppler weather radar (C-DWR) was installed at Thumba (8.537°N, 76.865°E), a coastal station in the southern peninsula of India known as “Gateway of Indian Summer Monsoon.” The C-DWR operates in the frequency range of 5.6 to 5.65 GHz with a peak transmitting power of 250 kW at 0.004 duty ratio and employs the state-of-the-art technology for both transmitting and receiving subsystems. Apart from providing regular base products such as reflectivity (Z), radial velocity (V), and spectral width (σ), the DWR being equipped with dual-polarization capability provides differential reflectivity (Zdr), differential phase shift (ϕdp), and correlation coefficient (ρhv). This is the first DWR with polarimetric capability developed indigenously in India. The C-DWR was operated during North-East as well as South-West monsoon period to evaluate its performance with special emphasis on the reflectivity and rainfall intensity measurements. Before the commencement of the campaign, the C-DWR was calibrated using a metallic sphere and the appropriate corrections were made to the radar constant. The preliminary results show that the radar products are consistent with present understanding of precipitating cloud systems. The simultaneous observations of precipitating clouds by C-DWR and Global Precipitation Measurement mission are used to evaluate the former. The comparison of spatial pattern of reflectivity from space-based radars and C-DWR shows very good agreement, qualitatively. The C-DWR-derived rainfall observations also show very good agreement with ground-based laser precipitating monitor measurements. The regression analysis between the C-DWR and laser precipitation monitor-derived rainfall shows a correlation coefficient of 0.89. The C-DWR observations during the passage of tropical cyclone Ockhi are also discussed. The significance of this study lies in describing the first indigenously developed C-band dual-polarization radar and its validation using the space- and ground-based observations.

Remote Sensing of Ice Conditions in the Southeastern Baltic Sea and in the Curonian Lagoon and Validation of SAR-Based Ice Thickness Products

Here we analyze ice conditions in the Southeastern Baltic (SEB) Sea and in the Curonian Lagoon (CL) using spaceborne synthetic aperture radar (SAR) data combined with in-situ measurements from coastal stations during four winter seasons between 2009–2013. As shown, the ice conditions in the SEB and in the CL are strongly varying from year to year and do not always correlate with each other. In the SEB, ice cover may form only within 5–15 km band along the coast or spread up to 100 km offshore covering almost the entire region. The mean ice season duration here is 45 days. The CL is almost fully ice-covered every year apart of its northern part subjected to sea water inflow and active shipping. The ice regime is also more stable here, however, it also possesses multiple periods of partial melting and re-freezing. In this study we also perform a validation of three SAR-based ice thickness products (Envisat ASAR 0.5-km and 1-km, and RADARSAT-2 0.5-km) produced by the Finnish Meteorological Institute versus in-situ measurements in the CL. As shown, all satellite products perform rather well for the periods of gradual ice thickness growth. When the ice thickness grows rapidly, all products underestimate the observed values by 10–20 cm (20–50%). The best results were obtained for the RADARSAT-2 ice thickness product with the highest R2 value (0.68) and the root mean square error around 8 cm. The results of the study clearly show that multi-mission SAR data are very useful for spatial and temporal analysis of the ice regime in coastal waters and semi-enclosed shallow water bodies where the number of field observations is insufficient or lacking.

The Mw = 5.6 Kanallaki Earthquake of 21 March 2020 in West Epirus, Greece: Reverse Fault Model from InSAR Data and Seismotectonic Implications for Apulia-Eurasia Collision

We identify the source of the Mw = 5.6 earthquake that hit west-central Epirus on 21 March 2020 00:49:52 UTC. We use Sentinel-1 synthetic aperture radar interferograms tied to one permanent Global Navigation Satellite System (GNSS) station (GARD). We model the source by inverting the INSAR displacement data. The inversion model suggests a shallow source on a low-angle fault (39°) dipping towards east with a centroid depth of 8.5 km. The seismic moment deduced from our model agrees with those of the published seismic moment tensors. This geometry is compatible with reverse-slip motion along the west-verging Margariti thrust fault that accommodates part of the convergence within the collision zone between Apulia and Eurasia. We also processed new GNSS data and estimate a total convergence rate between Apulia and Eurasia of 8.9 mm yr−1, of which the shortening of the crust between the Epirus coastal GNSS stations and station PAXO in the Ionian Sea (across the Ionian Thrust) is equivalent to ~50% of it or 4.6 mm yr−1. By back-slip modelling we found that a 60-km wide deformation zone takes up nearly most of the convergence between Apulia-Eurasia, trending N318°E. Its central axis runs along the southwest coast of Corfu, along the northeast coast of Paxoi, heading toward the northern extremity of the Lefkada island. The island of Paxoi appears kinematically as part of the Apulian plate.

Seasonal Shifts in Diazotrophs Players: Patterns Observed Over a Two-Year Time Series in the New Caledonian Lagoon (Western Tropical South Pacific Ocean)

Coastal and open ocean regions of the Western Tropical South Pacific ocean have been identified as a hotspot of N2 fixation. However, the environmental factors driving the temporal variability of abundance, composition, and activity of diazotrophs are still poorly understood, especially during the winter season. To address this, we quantified N2 fixation rates and the abundance of seven diazotroph phylotypes (UCYN-A1 symbiosis, UCYN-B, UCYN-C, Trichodesmium, Het-1, Het-2 and Het-3) on a monthly basis during two full years (2012 to 2014) at four stations along a coast to open ocean transect in the New Caledonian lagoon. The total nifH gene concentration (sum of all nifH gene copies) clearly decreased from the barrier reef to the shore. Apart from UCYN-B, which peaked at very high abundances (106-108nifH gene copies L-1) at two occasions at the coastal station, the UCYN-A1 symbiosis was the most abundant group at all stations, accounting for 79 % of the total nifH gene copy counts along the transect (average abundance 4.2 ± 10.3 x 104 nifH gene copies L-1). The next most abundant groups were in order Trichodesmium (accounting for 14% of the total nifH gene copies), Het-groups (6% of the total) and UCYN-C (1% of the total). Statistical analyses reveal that the UCYN-A1 symbiosis and Het groups were associated with cold ( 25°C) waters, low NOx and PO43- concentrations, strong and (mostly) easterly winds. Average N2 fixation rates over the survey were 6.5 ± 6.7 nmol N L-1 d-1 and did not differ significantly among seasons. The interannual variability was more pronounced with average integrated rates significantly higher the second year of the survey (162 ± 122 μmol N m-2 d-1) than the first year (66 ± 91 μmol N m-2 d-1), likely due to higher seawater temperature. This dataset suggests that seasonality is less pronounced than previously thought, and that relatively high N2 fixation rates are maintained in the New Caledonian lagoon all year long, despite seasonal changes in the diazotroph community composition.

Comparison based on the technical and economical analysis of wind energy potential at onshore, coastal, and offshore locations in Çanakkale, Turkey

Offshore wind technology in a global context is developing with extraordinary speed, and technical constraints are gradually decreasing. However, in Turkey, offshore applications are yet to be established despite the installation of a significant number of onshore wind power plants over the last ten years. The city of Çanakkale is situated on both the Marmara and the Aegean Sea. It is located on both sides of the Çanakkale Strait, which connects the continents of Asia and Europe and occupies an important geographical position in terms of wind-energy potential. In this study, the wind-energy potential was investigated using data from 18 different meteorological stations located at onshore, coastal, and offshore stations in Çanakkale. Weibull and Rayleigh probability density functions were used to obtain wind speed distribution curves. Four wind turbines with power ranging from 1500 kW to 4500 kW for onshore locations and three wind turbines with power ranging from 2000 kW to 5000 kW for coastal and offshore locations were compared in the scope of the methods used in economic analysis [energy cost estimation (C), net present value (NPV), benefit cost ratio, payback period, and internal rate of return]. In this context, the best performances were obtained in onshore locations of Bozcaada, Çanakkale Airport, and coastal and offshore locations of Bozcaada/Damlacık L. and Lapseki/Zincirbozan L. for Vestas V112 (119 m) turbine and Vestas V90 (105 m) turbine, respectively. This study aims to contribute scientifically to the development of coastal and offshore wind energy in the region.

Biological nitrogen fixation detected under Antarctic sea ice

Nitrogen fixation is the primary source of reactive nitrogen in the ocean. Most ecological models do not predict nitrogen fixation in the Antarctic Ocean because of the low availability of iron and high abundance of nitrogen. Here we extensively examined nitrogen fixation in the Antarctic Ocean, and found substantial nitrogen fixation (maximum: 44.4 nmol N l−1 d−1) near the Antarctic coast, especially around ice-covered regions. The nitrogenase gene (nifH) was detected at all coastal stations, including stations where no nitrogen fixation was found. At the stations where nitrogen fixation was detected, the nitrogen-fixing cyanobacterium UCYN-A (Candidatus ‘Atelocyanobacterium thalassa’) dominated nifH gene expression, and the nifH sequence was identical to that of the major oligotype in tropical and subtropical oceans. Our results suggest that marine nitrogen fixation is a ubiquitous process in the global ocean, and that UCYN-A is the keystone species for making it possible. Observational evidence of cyanobacterial activity in the Antarctic Ocean suggests that nitrogen fixation could be a ubiquitous process in the global ocean.

Spatial patterns and trends of extreme rainfall over the southern coastal belt of West Africa

The southern coastal belt of West Africa (SCWA) with its high population density and many major cities, combined to the low elevation and poor urban planning, is very vulnerable to floods resulting from extreme rainfall events. The aim of this paper is to analyze the characteristics of extreme rainfall in the SCWA during the 1981–2015 period, in terms of frequency, intensity, seasonality, and trends. Therefore, daily rainfall of 31 stations located in the southern part of Cote d’Ivoire, Ghana, Togo, and Benin and rainfall estimation products combining in situ observations and satellites rainfall estimation data have been used. For each station and pixel, the local 95th percentile (P95) computed on all rain days of at least 1 mm was used to define extreme rainfall events. Rainfall on the coastal belt is heavier than further inland, with P95 values reaching 82 and 52 mm/day for coastal and continental stations, respectively. Extreme rainfall along the coast occurs predominantly between May and July. Interannual variations of different indicators of extreme rainfall show a broad agreement between rain gauge data and rainfall estimates from CHIRPS (Climate Hazards Group InfraRed Precipitation with Station) data. In the southern part of Cote d’Ivoire and Togo/Benin, increase of number of extreme rainfall event (NP95) and stability number of days with rainfall less than P95 (NL95) are recorded, which induces an increase of total rainfall. But, in the southern part of Ghana, there is a stable total rainfall due to an increase in NP95 compensated by a decrease in NL95.

Global Warming Impacts Micro-Phytoplankton at a Long-Term Pacific Ocean Coastal Station

Understanding impacts of global warming on phytoplankton – the foundation of marine ecosystems – is critical to predicting changes in future biodiversity, ocean productivity, and ultimately fisheries production. Using phytoplankton community abundance and environmental data that span ~90 years (1931-2019) from a long-term Pacific Ocean coastal station off Sydney, Australia, we examined the response of the phytoplankton community to long-term ocean warming using the Community Temperature Index, an index of the preferred temperature of a community. With warming of ~1.8℃ at the site since 1931, we found a significant increase in the community temperature index from 1931-1932 to 2009-2019, suggesting that the relative proportion of warm-water to cold-water species has increased. The Community Temperature Index also showed a clear seasonal cycle, with highest values at the end of austral summer (Feb/Mar) and lowest at the end of winter (Aug/Sept), a pattern well supported by other studies at this location. The shift in CTI was a consequence of the decline in the relative abundance of the cool-affinity (optimal temperature = 18.7℃), chain-forming diatom Asterionellopsis glacialis (40% in 1931-1932 to 13% in 2009 onwards), and a substantial increase in the warm-affinity (21.5℃), also chain-forming diatom Leptocylindrus danicus (20% in 1931-1932 to 57% in 2009 onwards). L. danicus reproduces rapidly, forms resting spores under nutrient depletion, and displays a wide thermal range. Species such as L. danicus may provide a glimpse of the functional traits necessary to be a ‘winner’ under climate change.

The diurnal variability of precipitable water vapor derived from GPS tropospheric path delays over the Eastern Mediterranean

The study of the diurnal variations of the total water vapor amount in an atmospheric column, also known as Precipitable Water Vapor (PWV) or Integrated Water Vapor (IWV), is highly significant in meteorology and climatology studies, yet very limited due to insufficient spatial and temporal in situ measurements. Nowadays, Global Navigation Satellite System (GNSS) ground receivers are used along with retrieval techniques in order to conduct high sample rate PWV estimations. Here, we present the annual and seasonal PWV diurnal cycles extracted from the Survey Of Israel Active Permanent Network (SOI-APN) GNSS receivers in the Eastern Mediterranean region. The data period spans from 5 to 21 years, ensuring its suitability for studying the PWV annual and seasonal mean diurnal variations. We particularly focus on the summer months (JJA), where the Mediterranean Sea Breeze (MSB) plays a dominant role in transporting humidity inland. For most stations, the diurnal amplitude in summer is the highest compared to the seasonal mean (4%–21%), followed by spring, autumn and winter (2%–4%). The PWV in the coastal stations peaks at 6–7 UTC while the northernmost highland station peaks at 8 UTC and the southernmost at 14 UTC indicating frontal MSB propagation from the coastline eastward inland combined with northern winds enhancement due to Coriolis force. Moreover, for most stations, the PWV peak hour is correlated with the distance from the Mediterranean Sea shore, substantiating the MSB's role as a key driver of the PWV diurnal variability during summer months. The PWV minimum values in the coastal stations occurs between 14 UTC and 19 UTC while in the highland stations it varies from 17 to 00 UTC. The coastal stations' PWV amplitude, compared to the daily mean, is around 1 mm while the highland stations amplitude is 2–3 mm. In addition, a strong correlation between the PWV diurnal cycle and the atmospheric Mixing Layer Height (MLH) diurnal variations is found using ceilometer data, suggesting that the MLH modulates the PWV, however this conclusion requires further research. Finally, using harmonic analysis with the PWV diurnal variations in summer, reveals that the diurnal and the semidiurnal modes account for ~95% of the sub-daily variance in 19 out of 21 GNSS stations

Air Quality During COVID-19: Analysis of Particulate Matter for a Coastal Urban Station Visakhapatnam(India)

The last day of the year 2019 (December 31st), a new infection, coronavirus, was reported from Wuhan (China) to WHO. Subsequently, it was named COVID-19 disease and being declared pandemic on the 11thof March 2020. It was one of the ever faced challenges, and 40 to 60 percent of the world population was estimated to be affected by this virus. This led to severe crises in all countries in terms of economic, social, and environment, emphasizing health. To avoid transmission of this virus worldwide, the lockdown was implemented. This lockdown started on 23rd January 2020 in some parts of the world that impacted the environment and air quality of various cities, depending on their socio-economic conditions. As per the ESA (European Space Agency) and NASA (National Aeronautics and Space Administration), Wuhan experienced a 30% reduction in air pollution. It is a known fact that air pollution has a major impact on human health; the effect of lockdown in various cities and its impact on air pollution prompt us to review some of the recent results published in a nutshell. This paper presented some of the results related to air pollution before and after the announcement of lockdown in various cities around the globe, including Visakhapatnam (India) a polluted coastal urban station with more emphasis on PM2.5 and PM10 concentrations along with air pollutants like NO2, SO2, NO, CO and Relative Humidity.

The experience of remote temperature-water content sounding of atmosphere during drift of R/V “Akademik Tryoshnikov”

For the first time experience was gained with the operation of Russian equipment for water content and temperature remote sensing of the lower atmosphere in the Arctic. The comparison the results of measurements by radiometric systems with data of radiosoundings in wide range of meteorological conditions had been executed. It is shown that mean difference between integral atmospheric water content, measured by water vapor radiometer WVR, and calculated from radiosoundings data does not exceed 6 % with standard deviation 0.54 kg/m2 and significant correlation coefficient 0,92. Analysis the data of meteorological temperature profiler MTR-5 allows to conclude that in general its adequately reproduce air temperature profiles in the atmospheric lower 1000 m layer. Some deviations take place only in cases of large temperature gradients. Preliminary analysis of WVR data showed that monthly mean value of integral atmospheric water content in area under study in April 2019 year practically coincides with calculated from radiosoundings, performed in 1983—1988 years at the polar station Barentsburg, nearest to the drift region, 3.61 and 3.62 kg/m2 respectively. Same time hourly mean values of integral atmospheric water content during drift varied from 2 to 10 kg/m2, with extreme values recorded between April 15 and April 20, probably due to intensive transport of air masses of the Atlantic origin. Based on MTR-5 data it was concluded that despite differences in sounding technology, the place and time of observations, the statistics of inversions registered during drift correspond well to statistics of inversions, recorded on the Arctic coastal stations and over sea ice cover of the Weddell Sea in winter.

Shifts in the protist community associated with an anticyclonic gyre in the Alboran Sea (Mediterranean Sea).

The diversity of protists was researched in the Alboran Sea (SW Mediterranean Sea) by means of high-throughput sequencing technologies based on the amplification of the V9 region of 18S rRNA. Samples were collected at different depths in seven stations following an environmental gradient from a coastal upwelling zone to the core of an oligotrophic anticyclonic gyre (AG). Sampling was performed during summer, when the water column was stratified. The superphyla Alveolata, Stramenopila and Rhizaria accounted for 84% of the total operational taxonomic units (OTUs). The most diverse groups were Dinophyceae (21% of OTUs), Marine Alveolates-II (MALV-II; 20%), Ciliophora (9%) and MALV-I (6%). In terms of read abundance, the predominant groups were Dinophyceae (29%), Bacillariophyta (14%), MALV-II (11%) and Ciliophora (11%). Samples were clustered into three groups according to the sampling depth and position. The shallow community in coastal stations presented distinguishable patterns of diatoms and ciliates compared with AG stations. These results indicate that there was a strong horizontal coupling between phytoplankton and ciliate communities. Abundance of Radiolaria and Syndiniales increased with depth. Our analyses demonstrate that the stratification disruption produced by the AG caused shifts in the trophic ecology of the plankton assemblages inducing a transition from bottom-up to top-down control.

Надежность и точность систем контроля природной среды. Часть 2

The accuracy of field/process reconstruction from the field/process measurement data at the nodes of the space-time lattice is the main quality criterion for the control system. Due to the unreliability of the system, information from the lattice nodes is lost, which is equivalent to its thinning. There is an analytical connection between the error in the field representation and the number of nodes operating with a known probability. Approximate formulas estimating the increment of the error in the representation of processes and fields with power-law spectra with a decrease in the number of nodes N of the space-time lattice for are proposed. Real control systems are multichannel and retain partial useful operability in the event of a failure of a certain number of channels, i.e. they are redundant. Formulas for calculating the reliability of redundant shipborne sounding and towed devices, automatic buoy stations with meters on the horizons and with distributed thermopiles are derived. Towed systems, coastal stations and autonomous buoy stations should operate as long as possible. To build durable systems, the results obtained earlier in the theory of reliability by the author on the ineffectiveness of the static reserve, the fundamental inappropriateness of external diagnostics of faults by observing the inputs and outputs of devices, the possibility of ideal diagnostics of faults by replacing from the dynamic reserve are used. This is the only known method that provides optimal and ideal diagnostics of malfunctions regardless of the structure of the systems and, therefore, allows you to build recoverable and arbitrarily durable systems. The diagnostic method by replacing from the reserve in the software implementation is extended to a set of nodes of the space-time lattice for selecting information from the environment.

A Simple Empirical Band-Ratio Algorithm to Assess Suspended Particulate Matter from Remote Sensing over Coastal and Inland Waters of Vietnam: Application to the VNREDSat-1/NAOMI Sensor

VNREDSat-1 is the first Vietnamese satellite enabling the survey of environmental parameters, such as vegetation and water coverages or surface water quality at medium spatial resolution (from 2.5 to 10 m depending on the considered channel). The New AstroSat Optical Modular Instrument (NAOMI) sensor on board VNREDSat-1 has the required spectral bands to assess the suspended particulate matter (SPM) concentration. Because recent studies have shown that the remote sensing reflectance, Rrs(λ), at the blue (450–520 nm), green (530–600 nm), and red (620–690 nm) spectral bands can be assessed using NAOMI with good accuracy, the present study is dedicated to the development and validation of an algorithm (hereafter referred to as V1SPM) to assess SPM from Rrs(λ) over inland and coastal waters of Vietnam. For that purpose, an in-situ data set of hyper-spectral Rrs(λ) and SPM (from 0.47 to 240.14 g·m−3) measurements collected at 205 coastal and inland stations has been gathered. Among the different approaches, including four historical algorithms, the polynomial algorithms involving the red-to-green reflectance ratio presents the best performance on the validation data set (mean absolute percent difference (MAPD) of 18.7%). Compared to the use of a single spectral band, the band ratio reduces the scatter around the polynomial fit, as well as the impact of imperfect atmospheric corrections. Due to the lack of matchup data points with VNREDSat-1, the full VNREDSat-1 processing chain (atmospheric correction (RED-NIR) and V1SPM), aiming at estimating SPM from the top-of-atmosphere signal, was applied to the Landsat-8/OLI match-up data points with relatively low to moderate SPM concentration (3.33–15.25 g·m−3), yielding a MAPD of 15.8%. An illustration of the use of this VNREDSat-1 processing chain during a flooding event occurring in Vietnam is provided.

Quantifying the cooling effect of rain events on outdoor thermal comfort in the southern coastal stations of the Caspian Sea.

Pleasant outdoor thermal conditions depend on a wide range of climatic elements. The impact of rainfall events, as important climatic elements, on providing thermal comfort, has been less explored in the available literature. The work presented herein investigates the impact of Rainy Days as well as a Day Prior to (Dprior) and a Day Post rain (Dpost) events on thermal conditions in the southern coastal region of the Caspian Sea. In this study, rainfall events during 1961-2017 observational period were categorized based on their intensity. Then, human thermal comfort during non-rainy (sunny) and rainy days was estimated and compared by using the radiation-driven Physiological Equivalent Temperature (PET) index, Universal Thermal Climate Index (UTCI) and Perceived Temperature (PT) index. Furthermore, difference between the average of thermal conditions in rainy days compared to a day prior and a day post rain events was calculated separately for comfort, cold and heat stress thresholds of each bioclimatic index. Finally, the correlation between the average of indices for rainy days and the frequency of rainfall events of each specific year was computed. Results suggested that overall average of studied indices for all rainy days is lower than the average for days prior and post the rain events. PET index has shown to be most impacted and reduced as a result of rain events and therefore more indicative of a cool ing effect. The observed difference in total average of PET in rainy days compared to non-rainy days were 8.30°C, 5.86°C and 8.85°C for Babolsar, Rahst and Gorgan stations, respectively. Generally, the cooling effect of rain events on the temperature for a day prior rain events is higher than a day post rainfall. Finally, the trend analysis on rainy days in the studied period revealed that the average of bioclimatic indices in western stations (Babolsar and Rasht) are increasing whereas a decreasing trend was observed for Gorgan as more of an eastern station.

Study of the spatial and temporal variability of rainfall in the Middle and Lower Cheliff (Algeria)

Abstract. The purpose of this study is to identify homogeneous rainfall regions and to study the spatial and temporal variability of rainfall in the Cheliff basin using the regional vector method and the statistical approach (Pettitt test, Lee Heghinian test and Hubert segmentation) and the geostatistic approach (inverse distance weighting method). In terms of results, the regional vector method highlighted six (6) homogeneous rainfall regions. The downward trend occurred in the study area in 1972, affecting a few coastal stations. In 1976, this decline extended to the South West and throughout the coastal region. In 1980, the drop covered the entire basin. This decline has resulted in an estimated deficit of 30 % on average in the eastern region, the coastal region and the Mina. However, the central part of the basin experienced a 20 % decrease compared to the period before the break (1968–1980). The same spatial irregularity in rainfall was observed during the pre-break and post-break periods (1981–2010). On the other hand, throughout the basin, the areas corresponding to the rainfall ranges identified during the 1968–1980 period experienced an average decrease of 100 mm during the post-break period, except in the eastern region, where the decrease exceeded 200 mm.

Temporal variations in phytoplankton composition in the northeastern Sea of Marmara: potentially toxic species and mucilage event

Temporal variations in phytoplankton composition in the northeastern Sea of Marmara was investigated associated with physico-chemical variables from January 2004 to December 2007. The occurrence of potentially toxic species and a mucilage event was also evaluated during this study period. The confined upper layer of the Sea of Marmara is mesotrophic to eutrophic and has higher productivity when compared to the neighbouring Black Sea and Aegean Sea. 132 taxa in the micro-phytoplankton community were identified, 11 of which are known to be potentially toxic. The most abundant species were Pseudo-nitzschia species from diatoms and Prorocentrum micans from dinoflagellates. Potentially toxic species were more common at the coastal stations. The onset of a mucilage formation was observed in October 2007, and well-known mucilage producers such as Gonyaulax hyalina (reported as G. fragilis) and Thalassiosira gravida (reported as T. rotula) dominated the phytoplankton community during this event. A marked decrease in the number of species and diversity index following June 2007 and reported shifts in the zooplankton community during the same period points to probable cascading effects in the pelagic ecosystem of the Sea of Marmara.

Diurnal variation of precipitable water vapor over Central and South America

Annual and seasonal diurnal precipitable water vapor (PWV) variations over Central and South America are analyzed for the period 2007–2013. PWV values were obtained from Global Navigation Satellite Systems (GNSS) observations of sixty-nine GNSS tracking stations. Histograms by climate categories show that PWV values for temperate, polar and cold dry climate have a positive skewed distribution and for tropical climates (except for monsoon subtype) show a negative skewed distribution.The diurnal PWV and surface temperatures (T) anomaly datasets are analyzed by using principal components analysis (PCA). The first two modes represent more than 90% of the PWV variability. The first PCA mode of PWV variability shows a maximum amplitude value in the late afternoon few hours later than the respective values for surface temperature (T), therefore the temperature and the surface conditions (to yield evaporation) could be the main agents producing this variability; PWV variability in inland stations are mainly represented by this mode. The second mode of PWV variability shows a maximum amplitude at midnight, a possible explanation of this behavior is the effect of the sea/valley breeze. The coastal and valley stations are affected by this mode in most cases. Finally, the “undefined” stations, surrounded by several water bodies, are mainly affected by the second mode with negative eigenvectors. In the seasonal analysis, both the undefined and valley stations constitute the main cases that show a sea or valley breeze only during some seasons, while the rest of the year they present a behavior according to their temperature and the surface conditions. As a result, the PCA proves to be a useful numerical tool to represent the main sub-daily PWV variabilities.

C-band Doppler weather radar observations during the passage of tropical cyclone ‘Ockhi’

Recently, a C-band polarimetric Doppler weather radar (DWR) was installed and commissioned at Thumba (8.5° N, 77° E), a west coastal station in the southern peninsula of India known as ‘Gateway of Indian Summer Monsoon’, for monitoring severe weather events and tropical cyclones. The DWR operates in the frequency range of 5.6 to 5.65 GHz with a peak transmitting power of 250 kW and employs state-of-the-art technology for both transmitter and receiver subsystems. Apart from providing regular base products such as reflectivity (Zh), radial velocity (V) and spectral width (σ), the DWR being equipped with dual polarization capability provides additional products such as differential reflectivity (Zdr), differential phase shift (ϕdp) and correlation coefficient (ρhv), which are used to study the microphysical properties of rain bearing clouds. The ‘Ockhi’ cyclone was the most recent one from 29th November to 2nd December 2017, which caused large devastation in terms of both economic and human life in Kerala coastal places. The C-band polarimetric DWR provides an opportunity to investigate the spatial and vertical structure of ‘Ockhi’ cyclone over the south-west coast of Kerala. The cyclone ‘Ockhi’ developed near the west of Srilanka and later advanced and stretched out near south-east of Kanyakumari through the Arabian Sea and impacted the coastal places of Kerala on 1st December 2017. During its formative stage, the eyewall was not clearly visible. The cyclone eye was clearly seen at the well-developed stage of cyclone, when it was in the vicinity of DWR range. The overall spatial extent of cyclone is ~ 1000 km as seen in INSAT-3D images. The maximum surface wind speed was observed to be around 30 m/s near to the Kerala coast. The outer fringes of the cyclone were located above the Trivandrum and caused heavy rainfall on 30 November 2017 around 17 h. The C-band DWR has captured the various stages of cyclone ‘Ockhi’ and its primary bands. Observations of C-band polarimetric DWR indicates that the vertical cross section of reflectivity along the cyclone eye showed that the size of cyclone is around 20 km and the precipitating cloud top heights reaching as high as 10–12 km. The cyclone’s outer rainbands are slanted outward and were more intense than the inner rainbands. The area surrounding the cyclone eye is the eyewall, characterized by very strong wind and torrential rainfall. The large differential reflectivity values ranging from 2 to 3 dB are found in the eyewall and rainbands regions. The outer rainband is characterized by large Zdr values with high reflectivity above the melting layer. The different values of Zdr are observed in the eyewall and outer rainband regions, which suggest that different microphysical characteristics prevail. As time progress, the cyclone system gradually intensified and the eyewall became more intense compared to the outer ones. The present study utilizes the C-band polarimetric DWR observations to characterize the spatial and vertical structure of cyclone ‘Ockhi’ and provides the ample information on the polarimetric signatures of cyclone structure to improve the better understating on the microphysical characteristics of tropical cyclones.

Satellite and In Situ Monitoring of Chl-a, Turbidity, and Total Suspended Matter in Coastal Waters: Experience of the Year 2017 along the French Coasts

The consistency of satellite and in situ time series of Chlorophyll-a (Chl-a), Turbidity and Total Suspended Matters (TSM) was investigated at 17 coastal stations throughout the year 2017. These stations covered different water types, from relatively clear waters in the Mediterranean Sea to moderately turbid regions in the Bay of Biscay and the southern bight of the North-Sea. Satellite retrievals were derived from MODIS/AQUA, VIIRS/NPP and OLCI-A/Sentinel-3 spectral reflectance. In situ data were obtained from the coastal phytoplankton networks SOMLIT (CNRS), REPHY (Ifremer) and associated networks. Satellite and in situ retrievals of the year 2017 were compared to the historical seasonal cycles and percentiles, 10 and 90, observed in situ. Regarding the sampling frequency in the Mediterranean Sea, a weekly in situ sampling allowed all major peaks in Chl-a caught from space to be recorded at sea, and, conversely, all in situ peaks were observed from space in a frequently cloud-free atmosphere. In waters of the Eastern English Channel, lower levels of Chl-a were observed, both in situ and from space, compared to the historical averages. However, despite a good overall agreement for low to moderate biomass, the satellite method, based on blue and green wavelengths, tends to provide elevated and variable Chl-a in a high biomass environment. Satellite-derived TSM and Turbidity were quite consistent with in situ measurements. Moreover, satellite retrievals of the water clarity parameters often showed a lower range of variability than their in situ counterparts did, being less scattered above and under the seasonal curves of percentiles 10 and 90.