Mean Monthly Wind Research Articles

Effects of wind velocity and soil characteristics on dust storm generation in Hawr-al-Azim Wetland, Southwest Iran

Nowadays, dust storms are an important environmental problem in Iran (especially in Khuzestan Province). The Hawr-al-Azim Wetland is a source for generation of dust storms. One-third area of this wetland is located in Iran. In this study, dust discharge is calculated using wind velocity, mean soil grain size (D50) and soil dry density. Soil characteristics were determined by data collected from 16 boreholes drilled in this wetland. Distributions of D50 and soil dry density in the wetland were determined using ordinary kriging method. Then critical wind speed was calculated in different regions of the wetland. The wetland soil is composed of medium and coarse silty soil. The dust mass discharge has reduced from 2003. The maximum monthly dust discharge mass occurs in June and July (along with a mean monthly wind velocity of 4.42 m s-1 and 4.27 m s-1, respectively). Because of the little amount of clay particles and the high wind velocity, increased soil moisture content cannot help in neither raise inthe critical shear velocity nor decreased dust mass discharge. Also, the produced dust is transported towards Northwest Iran because the dominant direction of wind is 270° to 300° relative to the north.

Simulation of the 2014 Anomalous Warming in the Northeast Pacific

ABSTRACTThe Nucleus for European Modelling of the Ocean (NEMO) numerical model was used to simulate the North Pacific Ocean beginning in January 1960. The model had a horizontal resolution of 0.25o, 46 vertical levels, and employed a spectral nudging assimilation scheme that, unlike standard nudging, nudges only specific frequency and wavenumber bands. This simulation was nudged to the mean and monthly Levitus climatology of potential temperature and salinity. The model was forced with mean monthly winds, net heat flux, and precipitation from the National Centers for Environmental Prediction (NCEP). The simulation was used to study a recent intrusion of much warmer and less saline water than normal from the west into the Gulf of Alaska, beginning in December 2013 and lasting until at least the early summer of 2014. The observed surface temperature anomalies were more than 4 standard deviations above normal. The model reproduced these anomalies in both a qualitative and quantitative manner, reproducing the same scale of anomalies over the region. An anomalous increase in the North Pacific Current (NPC) was found in the model in 2012 and the beginning of 2013, in agreement with observations. This increase in the NPC is associated with the positive phase of the North Pacific Gyre Oscillation. The causes of the temperature anomalies in the Gulf of Alaska could be due to three key factors: (i) an anomalously high, positive, surface heat flux in 2013 over the greater North Pacific; (ii) a significant decrease in the eastward flow of the NPC starting in late 2013 (with an accompanying decrease in cold water advection) after a period of historically strong eastward flow; and (iii) weaker winds throughout most of 2013 accompanied, however, by a shift to stronger northward winds (with an accompanying increase in warm water advection) in late 2013.

A Surface Wind Extremes (“Wind Lulls” and “Wind Blows”) Climatology for Central North America and Adjoining Oceans (1979–2012)

AbstractThis study explores long-term deviations from wind averages, specifically near the surface across central North America and adjoining oceans (25°–50°N, 60°–130°W) for 1979–2012 (408 months) by utilizing the North American Regional Reanalysis 10-m wind climate datasets. Regions where periods of anomalous wind speeds were observed (i.e., 1 standard deviation below/above both the long-term mean annual and mean monthly wind speeds at each grid point) were identified. These two climatic extremes were classified as wind lulls (WLs; below) or wind blows (WBs; above). Major findings for the North American study domain indicate that 1) mean annual wind speeds range from 1–3 m s−1 (Intermountain West) to over 7 m s−1 (offshore the East and West Coasts), 2) mean durations for WLs and WBs are high for much of the southeastern United States and for the open waters of the North Atlantic Ocean, respectively, 3) the longest WL/WB episodes for the majority of locations have historically not exceeded 5 months, 4) WLs and WBs are most common during June and October, respectively, for the upper Midwest, 5) WLs are least frequent over the southwestern United States during the North American monsoon, and 6) no significant anomalous wind trends exist over land or sea.

A self-adaptive hybrid approach for wind speed forecasting

Wind power, as a promising renewable energy source, has environmental benefits, as well as economic and social ones. To evaluate wind energy properly and efficiently, this study proposes a hybrid forecasting approach that combines the Extreme Learning Machine (ELM), which rarely presents in literature on wind speed forecasting, the Ljung-Box Q-test (LBQ) and the Seasonal Auto-Regressive Integrated Moving Average (SARIMA) to enhance the accuracy of wind speed forecasting. The proposed hybrid method is examined by forecasting the mean daily and mean monthly wind speed of four wind speed observation sites located in northwestern China. The results confirm that, compared with other popular models (ARIMA，SARIMA，Back-Propagation neural network (BP) and ELM), the hybrid forecasting method improves the predictions of daily and monthly wind speed, which indicates that the developed hybrid method exhibits stronger forecasting ability. The forecasting results also suggest the hybrid approach has better generality and practicability in different wind farms.

Simulation of the 2001–02 Anomalous Intrusion in the Northeast Pacific

A numerical model, the Parallel Ocean Program (POP) was used to run a 46-year simulation of the North Pacific Ocean beginning in January 1960. The model had a horizontal resolution of 0.25°, 28 vertical levels, and employed spectral nudging that, unlike standard nudging, nudges only specific frequency and wavenumber bands. This simulation was nudged to the mean and monthly Levitus climatology of potential temperature and absolute salinity (SA). The model was forced with the mean monthly winds, sea level pressure, net heat flux, and precipitation from the National Centers for Environmental Prediction (NCEP).The simulation was used to examine the anomalous intrusions, previously observed from 2001 to 2002, of cooler and fresher (less spicy) water flowing southward along the coast of western North America. The simulated anomaly began in 1999 in the North Pacific, progressed southeastward towards the coast and then southward, at least as far south as southern California. The southward velocity signal, modulated by a strong annual cycle, reached Point Conception in 2000 while the temperature and SA anomalies arrived later, in 2002–03. The simulated velocity anomalies were eastward at about 3 cm s−1 in the northeast Pacific near 47°N in agreement with observations. Simulated coastal southward flow speeds reached 10–20 cm s−1 during the summer from 2000 to 2002.This intrusion was by far the largest to occur over the entire length of the simulation. It was also the only time during the simulation when the Victoria mode was positive (associated with enhanced flow to the east via the North Pacific Gyre Oscillation (NPGO)) and the Multivariate El Niño-Southern Oscillation (ENSO) Index (MEI) was negative (La Niña conditions), tending to cause a southward flow anomaly along the coast.

Simulation of Mixed Layer Depth in the Northeast Pacific Utilizing Spectral Nudging

Abstract A numerical model, the Parallel Ocean Program (POP), is used to run a 46-yr simulation of the North Pacific Ocean beginning in January 1960. The model has 0.25° horizontal resolution and 28 vertical levels, and it employs spectral nudging, which, unlike standard nudging, nudges only specific frequency and wavenumber bands. This simulation is nudged to the mean and annual Levitus climatological potential temperature and salinity. The model was forced with National Centers for Environmental Prediction (NCEP) mean monthly winds, sea level pressure, net heat flux, and rain rate. The simulated mixed layer depths (MLD) suggest significant shoaling of the MLD between 1970 and 2006, with faster rates in the northern Gulf of Alaska and slower rates to the west and south of Line Papa. The rates are of similar magnitude to those found in past studies and are consistent with the observed freshening and warming of the upper waters in the Gulf of Alaska. The rates are not spatially uniform, and the simulated MLD in the northeast Pacific actually deepens with time at some locations. These regions of increase form zonal bands in the simulation. The simulated MLD at Ocean Weather Station Papa (OWSP) shoals on average, but it is located close to one of these deepening bands. On average, the simulated, low-frequency MLD at OWSP gives a good indication of the MLD along Line Papa and in the Gulf of Alaska near Line Papa’s latitude. The correlation coefficient between the MLD at OWSP and the latitudinal average of the MLD within the greater Gulf of Alaska (with OWSP removed) is 0.7 at zero lag. The correlation coefficient between the MLD at OWSP and the latitudinal average along Line Papa alone (with OWSP removed) is 0.6 at zero lag. Observed variability of the MLD along Line Papa and at OWSP is reproduced by the model. However, there is considerable spatial variability in the simulated MLD in the Gulf of Alaska as a whole, so MLD variability at OWSP is not necessarily a good indicator of the MLD variability throughout the region. Over the span of the simulation, the low-frequency MLD variability in the Gulf of Alaska is better correlated to the North Pacific Gyre Oscillation (NPGO) than to either the Pacific decadal oscillation (PDO) or Southern Oscillation index (SOI).

Spatial and Temporal Changes of Suspended Matter in Relation to Wind and Vegetation Cover in A Mediterranean Shallow Coastal Environment

Seasonal and spatial changes in seston, (POC), particulate organic carbon, (PON) particulate organic nitrogen and chlorophyll-a concentrations were studied on a monthly basis in a Mediterranean shallow coastal area (Stagnone di Marsala, Western Sicily) in order to gather information on factors controlling particulate organic matter distribution and composition. Seston concentration and composition were connected to the main physicochemical and biological driving factors, such as temperature, salinity, dissolved oxygen, wind-speed and biomass of submerged vegetation. the Stagnone di Marsala is characterized by high temperatures with strong seasonality (range: 11–28°C), while values ranged from 33 to 45 salinity. Total suspended organic matter concentrations (by ignition loss) ranged from 2 mg l−1 (in summer) to 12mgl−1 (in winter) and chlorophyll-a concentrations from 0.02 to 2 μgl−1. Despite a low POC/PON ratios (ranging from 5 to 11), the ratio of POC to chlorophyll (CHL-a) displayed very high values (annual average of 647). the data reported in this study, highlighting the oligotrophy of the Stagnone di Marsala area, indicate that the trophic state of the basin was controlled by different degrees of wind exposure (mean monthly wind velocity at exposed sites ranged between 4.2 and 6.7 m s−1) and by gradients in vegetation cover. These two factors induced clear changes in the concentration and composition of the suspended particles, but played a different role in exposed and sheltered areas. Exposed areas with limited vegetation were characterized by large resuspension processes and wide temperature and salinity fluctuations caused by wind induced turbulence. in these areas, autotrophic biomass (as chlorophyll-a), due to phytoplankton and/or re-suspended microphytobenthos, appeared to play an important

The Relation of Seafloor Voltages to Ocean Transports in North Atlantic Circulation Models: Model Results and Practical Considerations for Transport Monitoring*

Motionally induced voltage differences offer one of the few observational methods sensitive to changes in large-scale ocean transports. They present a useful contrast to most oceanographic data by virtue of their natural spatial integration, temporal continuity, and potentially long duration. However, widespread oceanographic use of the voltages observable with seafloor cables has been impeded by uncertainties of interpretation. Interpretation in terms of volume transport fluctuations has proved successful in the Straits of Florida and for a short cable in the easternmost part of the Bering Strait. Still, a number of older experimental studies resulted in disappointment, the Bering Strait work has been little known, and the Florida success might be a special case. The question considered in this paper is: Does a linear relationship between net transport and voltage difference fluctuations hold for long, open-ocean cables? This question is addressed by using a numerical model based on two years of results from the WOCE Community Modeling Effort, which simulated the wind-driven and thermohaline circulation in the North Atlantic using mean monthly winds and realistic topography with a resolution sufficient to permit mesoscale eddies. The model includes the effects of spatial and temporal variations of seawater temperature and salinity, electric current loops, the effects associated with the meandering of ocean currents over realistic topography and sediment thickness, realistic earth conductivity, and the spatially varying geomagnetic field. The main result is that the relationship between voltage and net cross-cable transport fluctuations can be remarkably linear over long distances. In view of the difficulties of long-term, large-scale transport monitoring by other methods, the implication of this work is that well chosen and carefully interpreted voltage observations hold great promise. This should be explored through renewed modeling, observation, and interpretation efforts.

Motional induction in North Atlantic circulation models

Motionally induced voltage differences provide one of the few observation methods sensitive to fluctuations of large‐scale ocean transports. However, uncertainties of interpretation have impeded widespread oceanographic use of voltages measured on open‐ocean cables. To resolve these uncertainties, we have developed a numerical simulation of the flow‐induced voltages in general circulation models. The model includes the effects of flow meandering, the spatial and temporal variations of seawater temperature and salinity, three‐dimensional Earth models with realistic sediment conductances, and the full physics applicable to the large‐scale, long‐period circulation when self‐induction may be neglected. For the oceanographic input, we used the World Ocean Circulation Experiment Community Modeling Effort's model, which simulates the wind‐driven and thermohaline circulation in the North Atlantic using mean monthly winds and realistic topography with resolution permitting mesoscale eddies. The results are in good agreement with the experimental cable calibration results from the Straits of Florida and with the Mid‐Ocean Dynamics Experiment. We find less influence of large‐scale electric current loops on the seafloor horizontal electric field than has previously been feared, our results supporting a local relationship of the seafloor electric field and ocean transport and the interpretation of seafloor horizontal electric field measurements in terms of local transport over much of the North Atlantic basin.

Sodar observations of the nocturnal boundary layer at Kharagpur, India

Sodar has been installed at Kharagpur (22.2 ° N, 87.3 ° E) as a part of the MONTBLEX-90 experiment and data were collected during the monsoon period. The variation of the nocturnal boundary layer (NBL) during the monsoon period is discussed. The height corresponding to the low-level wind maximum in the sodar wind profile during night time is identified as the NBL height. Mean monthly winds for July and August, plotted as time-height cross sections, reveal the height of the ground-based stable layer. The average NBL heights in the months of July and August are found to be 324 m and 296 m respectively. It is observed that the NBL height is relatively high in the month of July (active phase of monsoon) compared to that during August (weak phase). The months of July (total rainfall = 901 mm) and August (total rainfall = 134 mm) are associated with cloudy and relatively clear sky conditions. This indicates that clouds (through their effect on longwave cooling to space) play an important role in determining the NBL height during the monsoon.

Mean monthly wind driven climatological circulation model of the Bay of Bengal

A special feature of the Bay of Bengal circulation is its seasonal variation in response to the monsoonal winds. In the case of the Bay of Bengal, observationally very little is known about the large scale circulation. Theoretically, the problem of driving the circulation in the Bay of Bengal is more complex than that in other basins because of the presence of large quantities of fresh water discharge from Ganga-Brahmaputra-Meghna river systems, and also because the atmospheric driving forces even within a season are highly variable with frequent occurrences of tropical disturbances. Exploring the nature of the circulation in the Bay of Bengal is a problem of great importance in itself as well as for the critical role this region plays in the genesis of tropical disturbances which are the main source of large scale rainfall over the northern part of the Indian subcontinent. The surface circulation of the Bay of Bengal may, therefore, help in understanding the variation of rainfall over time scales ranging from the subseasonal to the interannual. Keeping this in view, an attempt was made towards the development of an oceanic climatological circulation model for the Bay of Bengal, which explains the seasonal variability of the currents. The model is fully non-linear and vertically integrated, with realistic basin geometry. The treatment of coastal boundaries involves a procedure leading to a realistic curvilinear representation of the western and eastern sides of the Bay of Bengal. This coastal representation has the advantage of taking into account the finer resolution in the shallow regions of the northern Bay. The model is forced by the monthly mean wind stress derived from 30 years (1950–79) of Comprehensive Oceanographic Atmospheric Data Sets (COADS). Special emphasis is given to the southern open boundary condition for the model. For this purpose, sensitivity experiments have been performed with six open boundary conditions and a comparative study of the results has been made. These sensitivity tests for the open boundary condition will help the development of a suitable coupled ocean-atmosphere model for this region. The model-generated main features are in general agreement with the known climatological circulation of the Bay of Bengal.

OUTLOOK ON NORTHEAST MONSOON RAINFALL OF TAMIL NADU

The mean monthly wind vectors at 850, 500 and 150 hPa levels over Thiruvananthapuram (TRV) and Madras (MDS) for August. and September have been subjected to stepwise screening. The objective is to develop a scheme capable of providing an outlook of .northeast monsoon rainfall of Tamil Nu in the beginning of October. A multiple regression scheme of S1K predictors has been identified. The scheme developed from 23•year data performed well when te.ted in an independent five-year period.

Coupled sea ice‐mixed layer simulations for the Southern Ocean

A coupled sea ice‐mixed layer‐pycnocline model for the Weddell Sea (Lemke et al., this issue; Owens and Lemke, this issue) is extended to the entire sea ice area around the Antarctic continent. The monthly atmospheric forcing and the annual oceanic forcing are specified from climatology. Sensitivity runs were performed with a fixed mixed layer, without snow cover, with a different ice strength constant (P*) and a varying e‐folding constant for the closing of leads (h0), without dynamics, and without ocean currents. Since the atmospheric forcing fields, although derived from large, historical data sets, differ considerably depending on the analysis technique, alternative wind, temperature, and precipitation forcing has been applied. Finally, the model has been forced with mean monthly winds supplemented by stochastic variations representing short‐term variability. The model results are compared with analyses of satellite data as well as with single measurements, and with simulation results from earlier models.

Statistical relations between winter monsoon Rainfall and the preceding summer monsoon

The mean monthly wind vectors at 7 standard isobaric levels and surface parameters of several stations of the summer (southwest) monsoon months of June to September over India have been examined. The objective was to select predictors for the northeast monsoon rainfall of the Indian Peninsular subdivisions of TamilNadu, Kerala, coastal Andhra Pradesh and Rayal3seema. The data for a 33-year period (1951-83) were used in this study. A sequence of screening tests were employed to select reliable predictors for these subdivisions. It has been shown that the August-September 150 mb zonal mean wind of Trivandrum is capable of giving satisfactory forecasts for the following northeast monsoon rainfall of Tamilnadu. The constraints in using multiple predictors have been discussed.

Regression equations between mean wind power density and mean hourly wind speed during the monsoon season

Utilising the hourly wind speed data of some selected Indian stations with good wind regime during the monsoon season, mean dally and monthly wind power density and mean daily and monthly wind speeds have been obtained for each day and for each month. From these, correlation coefficients between mean daily power density and cube of mean daily wind speed and also between mean monthly power density and cube of mean monthly wind speed have been computed for the monsoon months. These correlations are found to be consistently very high (> 0.92) and stable. In view of this very close and stable relationship, regression equations have been obtained between the mean daily wind power density and the cube of mean daily wind speed, as well as between the mean monthly wind power density and the cube of mean monthly wind speed during the monsoon season. The constants in these equations are found to have a linear relationship with the mean wind speed. These equations were applied to independent data to estimate the mean wind power density for the monsoon season from the mean wind speed and the estimates for the different stations were generally found to be within 15 percent of the mean power for the season as computed from the hourly wind speed data for the independent period. The equations have the potential of application to mean wind, speed from the cup anemometer data which are available from a large number of stations in India, for estimation of mean wind power density during the monsoon season.

A Newly Found Jet in North Kenya (Turkana Channel)

Abstract On the basis of recent pilot balloon observations which have become available in northern Kenya, it is shown that there exists a strong southeasterly low-level jet in the Turkana Channel which separates the Ethiopian Highlands the East African Highlands. The jet exists throughout the year, with speeds exceeding 30 m s−1 (60 kt) on a number of occasions and sometimes exceeding 50 m s−1 (100 kt). During February and March, the mean monthly winds based on the morning observations exceed 25 m s−1 (50 kt). The morning winds are stronger than afternoon winds, presumably due to stronger vertical mixing and dilution of the jet maximum in the afternoon. The hodograph turns in a counterclockwise direction from the lowest levels up to 0.75 km (2500 ft) above ground level and sometimes even aloft. Up to 0.45 km (1500 ft) above ground level, the hodograph manifests some of the characteristics of the Southern Hemisphere Ekman layer. This jet is different from the now well-known East African low-level jet (Find...

ATMOSPHERIC CIRCULATION AT ALTITUDES UPTO 37 KM OVER INDIA IN THE LATITUDE BELT 17°-19°N

Mean monthly winds in the 7-37 km range for the months, of September to May through December, based on 155 balloon ascents made over the period 1957-00 in the latitude belt 17*-10QN in India, are reported. It is shown that except for few short periods during winter and spring, when weak westerlies prevailed, the stratospheric circulation was predominantly zonal with winds generally increasing with altitude.