The increasing population on the southern Caspian coasts, industrial development, and increasing microbial pollution, chemical pollution, and oil pollutants resulted in an environmental crisis in the sea. Also, the increasing mean temperature of the Earth caused by global changes changed the rate and level of surface water at the entrance of the southern Caspian, and changes in the rate of rainfall, together, have forced changes in the pattern of meteorological systems in the region [1].

Despite the fact that the Caspian Sea has a history of observations of currents spanning more than half a century [2], there is a lack of data for an adequate reconstruction of the climatic circulation of seawater and its seasonal variability. This is because most measurement campaigns were short-term, conducted in coastal areas of the deep-sea Caspian Sea, and characterized by a small number of observational data ([3-6].

Many studies have been done on current characterization and measurement around the world. During the research cruise of Mt. Mitchell of loat, the Persian Gulf flow properties were measured via an ultrasonic Andra current meter in 5 mooring stations from March 2 to May 30, 1993, and were published by Abdolrahman. Ahamad [7] characterized the circulation of Sho'aibah lagoon, located on the Red Sea east part, from February to June and September to November of 1989.

These measurements were carried out at the surface level of the sea on 7 steps, each lasting 25 hours. In these measurements, an EN-DECO mechanical current meter was used. The study of Caspian Sea currents first started at the end of the 19th century, and the first results were presented by N.N.Putshina in 1877 upon navigation measurements. Afterwards, other maps based on apparatus measurements were presented [8]. Along with the development of field measurements on Caspian Sea stations and numerical models, the circulation regime at the northern, southern, and central parts of these locations was identified. The studies show that in the southern parts of the Caspian Sea, the wind-generated currents (flows) result from the differences between density and groundwater streams [9]. The speed and direction of current at the depths of the southern Caspian were first measured from May 31, 1977, to August 16, 1977, by a Radon research ship. On this research cruise, the metrological parameters and water physical and chemical parameters at the Southern Caspian Sea were studied. Russian (CASPY) surveys have measured 200000 cases. In this region, in spring, the velocity of currents reaches 6-8 m/s and in summer, it reaches 2-4m/s [10].

Zaker [11] presented the results of the first in situ current velocity observation of the southern continental shelf of the Caspian Sea adjacent to Iran, conducted for 254 days between August 2003 and April 2004.

Smith [12] studied the thermal wind relation held for the alongshore components of current. The major low-frequency fluctuations in the current (at 20 m and deeper) are barotropic, experienced equally at all depths, and highly correlated with sea level variations. Spectral analysis shows very high mutual coherence between wind, sea level, and clockwise currents only in a narrow band at 0.15 cpd [12].

The temperature structure in the study area is characterized by a strong seasonal thermocline, located between 20m and 50m depths with a 15^oC difference across it in the summer. In autumn, the thermocline gradually weakens, and at the end of winter, it disappears before its reformation in the early spring. The temperature in the surface layer ranges between 25 and 30^oC in summer, gradually decreases to 15^oC at the end of autumn, and remains mainly between 14-15^oC in winter. Below the thermocline, the temperature ranges between 10.5^oC and 7.5^oC at 110m depth, with small seasonal variations [13]. The salinity in the study area has small vertical and horizontal variations with slight seasonal changes. Salinity mainly ranges between 12.1 and 12.35 vertically in the summer and autumn. In the spring, lower salinities in the surface layer (11-12) are observed due to an increase in the local river inflows [13].

In the Southern Caspian Sea, measurements of velocity and direction of currents were only performed in Amirabad and Anzali ports. According to surveys on the resources of navigation, port organizations, other organizations, and related universities, no research was conducted concerning measurements of the current characteristics of Noshahr port. Hence, the study of the patterns of the southern Caspian currents could be an effective step toward understanding their effects on regional atmospheric systems and environmental problems and issues. Because of the importance of Noshahr port in navigation activities and military targets, and also for not having done such measurements on these coastlines so far, it is mandatory to conduct data measurements and processing of flow.

Study Area

Noshahr is located at 51, 30? N and 36, 39? E and has borders with the Caspian Sea to the north, the Alborz Mountains to the south, the town of Noor to the east, and the town of Chaloos to the west. The altitude is 2.9m below sea level. The Noshahr port is one of the main economic and commercial ports of Iran, with a high annual mass of goods for transactions. This port is the nearest port to Iran's capital (Tehran) and is equipped with an airline. The distance from the port to Tehran is 200 km. Figure 1 illustrates the geographical position of the Noshahr coast. The southern coast of the Caspian Sea has a subtropical climate characterized by warm, humid summers and mild, wet winters [14-16].

Figure 1: Geographical Position of Noshahr Coast.

Data Collection

Current measurement was performed on the Noshahr coast using the Eulerian method, using an electromagnetic current meter. In the Eulerian method, speed, quantity, and direction of flow are obtained through direct measurement. The Lagrangian method is used to obtain quantitative general information on flows. The limitations of Eulerian methodology are installation conditions, equipment maintenance, and the high expenses of measurements. However, Lagrangian methods cannot retrieve the exact velocity and flow direction in the studied region.

Current data are attained directly during measurement. After setting and preparing the vale port (V Midas) electromagnetic current meter, the station location with a predetermined longitude was referred to, and measurements began. This electromagnetic current meter has a memory capacity of 16 Mb, and its ability to measure flow velocity is about 0-5 m/s and flow direction is 0-360 degrees (±1 degree, figure 2).

The Abed vessel, which belonged to the navigating and ports of 57hs, supported the field campaigns (Fig 3). The current meter was moored at a predetermined depth, and then it began gathering data from flow characteristics. Simultaneous with velocity measurements and the direction of sea water flow, via a sampler apparatus of water altogether with revocable thermometers, sample sea water was collected and temperatures from different depths were recorded. Also, the saline parameters were recorded from the data of the Noshahr meteorology station, and the air temperature data was recorded by a mercury thermometer at sea level as well. Also, in order to determine the position of stations, a G.P.S. was used.

Figure 2: Midas Model of Vale Port Electromagnetic Current Meter.

Figure 3:  Abed Vessel.

Figure 4: Portable Salinometer.

Current measuring on Noshahr port coastlines was assisted by the navigation and ports organization, with limited facilities and under difficult conditions. Using the map, the important locations for the current meter were selected. Then, the equipment was positioned, the direction of movement was recognized, and it stopped in the specified afloat location. The latitude and longitude and the depth of the measurement station are shown in the table1. Figure 5 shows the location of measurement stations. Measurements were performed in 3 stations at depths of 10, 20, and 30 meters and in 2 separated transects. The reason for choosing these depths for measurement is to consider the conglomerate layer depth and the effect of wind and waves on the creation of coastal currents in the region. In each station, the current meter was installed in the middle. So, the place to install the current-meter equipment is at depths of 5, 10, and 15m. The duration of sampling for every transect is at least one day. The sampling was carried out twice during 2010-11 for two warm and cold seasons. The first step of sampling was done on August 24-27, 2010. The second step of sampling was done on March 3-5, 2011.

Table 1: Geographical Attitudes and the Depth of Measurement Stations.

Figure 5: Location of Measurement Stations in Noshahr Coast.

The sampling was done at six stations, according to table1. Simultaneously, the related physical data were measured from surface to depth in each station (water temperature, electrical conductivity, salinity, and light penetration depth). In order to calculate statistical indexes and draw diagrams, we used the software Excel, Spss, Dadisp, and Data log 400. Outlier data were omitted by current-meter software, and the data that required correction were corrected. To omit outliers, the software relies on their correlation diagram. In the electromagnetic current meter, the wave action, water surface movements, and the passage of other boats led to some wrongly recorded data. The spurious data caused by these mistakes were omitted. In some specific time, sudden movement of the apparatus (resulted from stresses created by waves or wind) has caused deviation in direction; considering existing data, some data were corrected. In the case of speed, because of the same cause or because of apparatus defection, some data with a low error coefficient were corrected. Current data processing was done using Excel and other related statistical software. Mazandaran province's metrology administration measures coastal metrological data in coastal cities of this country, such as Noshahr port. These data are measured every 3 hours during the day. The measured and attainable data are weather temperature, water temperature, height, wave period, climate humidity, wind direction, and speed.

For data processing, the data were first verified using the current-meter software. Then the data were spectrally analyzed. For that, the spectrum of current speed with a low-pass filter and disconnection frequencies of 0.1 p/s for measuring stations was computed. These frequencies were used to omit temporary effects or low-period currents. Figures 6-13 show the time series of the current speed component and their spectrum with a related filter in measuring stations at Noshahr port. In station 1, from winter, the current with frequency 0.012 to 0.02 has peaks of 111 to 95.2 second periods (˜ 2 minutes). This period specifies the current of water created by wind, or else the wave that has created this current at the coast is caused by wind. Most of the peaks of current frequencies in the studied stations indicate that water current resulted from wind in Noshahr port. Waves' facture resulted from wind on Noshahr coasts also make currents happen. The period of these waves in the study region is less than 5 seconds. So it can be concluded that in Noshahr coastal lines, wind plays an effective part in making sea currents. The average amounts of current velocity in the depth of 5m during the summer are measured for the 1st, 2nd, 4th, and 6th stations to be, respectively, 1.8, 1.59, and 2.01 m/s. These amounts of current velocity at a depth of 5m during winter at the 1st, 2nd, 4th, and 6th stations are respectively 1.05, 0.56, and 2.22 m/s. On figures 14-21 the changes in current direction for the understudied stations are drawn with time. The changes in current direction at most stations are periodic. The average of water’s current direction in the 1st, 2nd, 4th, 6th stations in the summer is respectively 83.6, 29.5, 68.9, and 96.9 degrees. These amounts of current for the same stations in the winter are respectively 223.8, 224.3, 72.4, and 24. The direction of the dominant currents in the understudied region in the summer is north-east, and in the winter it is northwest to northeast.

Figure 6: Time Series Component of Current Velocity and the Plan of Its Spectrum with Low Pass Filter and Disconnection Frequency of (0.01 And 0.1) in the winter for the First Station.

Figure 7: Time Series Component of Current Velocity and the Plan of Its Specturm with Low Pass Filter and Disconnection Frequency of (0.01 And 0.1) in the winter for the Second Station.

Figure 8: Time Series Component of Current Velocity and the Plan of Its Specturm with Low Pass Filter and Disconnection Frequency of (0.01 And 0.1) in the winter for the Forth Station.

Figure 9: Time Series Component of Current Velocity and the Plan of Its Specturm with Low Pass Filter and Disconnection Frequency of (0.01 And 0.1) in the winter for the 6th Station.

Figure 10: Time Series Component of Current Velocity and the Plan of Its Specturm with Low Pass Filter and Disconnection Frequency of (0.01 And 0.1) in the summer for the 1st Station.

Figure 11: Time Series Component of Current Velocity and the Plan of Its Specturm with Low Pass Filter and Disconnection Frequency of (0.01 And 0.1) in the summer for the 2nd Station.

Figure 12: Time Series Component of Current Velocity and the Plan of Its Specturm with Low Pass Filter and Disconnection Frequency of (0.01 And 0.1) in the summer for the 4th Station.

Figure 13: Time Series Component of Current Velocity and the Plan of Its Specturm with Low Pass Filter and Disconnection Frequency of (0.01 And 0.1) in the summer for the 6th Station.

Figure 14:  Current Direction Changes in the First Station of Noshahr Coasts in the winter.

Figure 15:  Current Direction Changes in the 2nd Station of Noshahr Coasts in the winter.

Figure 16:  Current Direction Changes in the 4th Station of Noshahr Coasts in the winter.

Figure 17:  Current Direction Changes in the 6th Station of Noshahr Coasts in the winter.

Figure 18: The Changes of Current Direction in the 1st Station of Noshahr in the summer.

Figure 19: The Changes of Current Direction in the 2nd Station of Noshahr in the summer.

Figure 20: The Changes of Current Direction in the 4th Station of Noshahr in the summer.

(T=1000/95*95(1/2) =21.05 sec. For example, at the first station in the winter, the time series of the component toward east-west and north-south, the water’s current velocity, and its spectrum with a low passage filter and disconnection frequency of 0/1 and 0/01 p/s were planned (Fig. 22). For the component toward east-west, the current velocity of water peaks is shown in green, and for the component toward north-south, the sea water’s current velocity is shown in red (Fig. 23). Considering the resulted numbers, it can be concluded that periods of 0.1 second to about 40 seconds are related to waves resulted from wind, and those of 57.05 and 95.2 are related to gravity waves and waves resulted from wind. The velocity of water current toward east-west shows that the intensity of waves resulted from wind is higher than that of gravity waves.

In the north-south component, the velocity of gravity waves and seich waves is higher than that resulting from wind. The spectra show that toward the north-south component, the intensity of waves resulted from wind and gravity waves is higher than the same waves toward the east-west. The direction of the dominant wind is toward the north-south direction and toward the direction of the component of seawater's current velocity.

The average amounts of current velocity at 5, 10, and 15m of depth in the summer and winter at Noshahr Port coastlines measuring stations are shown in tables 2 and 3. The amount of current velocity in the diagram mood, in depth, will be reduced by the friction of the base. The highest amount of current velocity was received at No. 6 station, far from the Behjataabaad coast, for the summer and winter. The lowest current velocity was received at the 2nd station, far from the Mashlak Bridge coast, for summer and winter. The construction of Noshahr port’s jetty is effective in weakening the waves and regional currents, and thus it has reduced the current velocity at the second station. Based on the results of measurements, the western coasts of Noshahr have higher turbulence and water movement than the eastern coasts. The general pattern of current in this region is east-northeast, and this pattern follows the wind blow. At the depths, compared to other parts of the southern Caspian, the velocity of water current is relatively high. The reason for such high speeds can be due to the high gradient of this region, which reinforces the movement of water mass toward the bottom of the gradient. However, the velocity of water current is reduced in all stations because of the friction among layers and the friction of the base with the increase in depth.

Figure 21: The Changes of Current Direction the 6th Station of Noshahr in the summer.

Figure 22: Time Series Component on East-West and North-South Current Velocity and Its Spectrum with Low Pass Fitter Fort The1st Station in the winter, Noshahr Coastlines.

Figure 23: At the 1st Station, in the winter, for Component on East-West, the Velocity of Current Picks and for North-South are shown by Green and Red Colours Respectively.

On numerical models of current in the south Caspian Sea, the velocity of 0.1 m/s and 0.5 m/s beside Iran’s coastline is attained. Also, the direction of current based on the results of numerical models is from west to east, and the results of this research show a good agreement with the studies.

1. The paradigm of velocity and direction of current, along with depth based on field measurements, were attained in the summer and winter for Noshahr coastlines. The general model of current in this region is east-northeast, and these models follow the wind direction. Also at depths, compared with other parts of southern Caspian, the velocity of water current is rather high. The reason for such high velocity could be the high gradient of this region.
2. Based on data measurement and processing results of current velocity, it became clear that on the west coasts of Noshahr port, turbulence and movement of water are higher than on the east coasts.
3. The highest velocities of water current on the layer beside the surface of Noshahr coastlines during winter and summer for the station far from Behjataabaad (station 6) are 2.22 and 2.01 m/s, respectively. The lowest velocities of water current on the layer beside the surface during summer and winter for the second station (beside Mashlak Bridge) are 0.69 and 0.41 m/s, respectively.
4. The data spectrum of current velocity with a low-pass filter and disconnection frequencies of 0.1 and 0.01 p/s for measurement stations was drawn. These disconnection frequencies were used to omit temporary effects, noises, or currents with very low periods. At the 1st station, in the winter, current with frequencies of 0.12 to 0.02 has peaks with periods of 111 to 95.2 seconds (almost 2 minutes). This amount of time indicates the water current resulted from wind, or the wave that has made this current on the coast is resulted from wind. Most of the peaks of the attained current frequencies in the study stations indicate the water current resulted from wind at Noshahr port coastlines.

With regard to the importance of Noshahr port in the Southern Caspian Sea and the few studies done by native scholars in this region, here are some suggestions:

1. Using different kinds of current meters for different depths at Noshahr port coastlines.
2. Construction of current meters at Noshahr port coasts at different depths and in different seasons for long periods, with the aim of studying the effect of this region’s currents on coastal weather, coastal line transformation, and the rate of sediment transition.
3. Measuring physical parameters (temperature, salinity, and density) in different seasons with more stations in the region.
4. Setting up automatic stations for marine meteorology and installing measurement apparatus for physical parameters (temperature, salinity, and density) out of the Noshahr port pond and the continuous measurement of the mentioned parameters.

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