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1.
Interannual variability of the upper layers of the tropical Atlantic is described based on in situ data. An objective analysis used all available temperature observations of the upper tropical Atlantic between 1979 and 1999 to construct a 4D database. Wind data are used to investigate potential mechanisms which might explain the observed variability. Four remarkable events are described: 1983–1984, 1988–1990, 1994–1995 and 1997–1998. Three of them are characterised as equatorial (1983–1984, 1994–1995, and 1997–1998). The 1988–1990 event is a basin-wide phenomenon which does not involve the same mechanisms as the other three. Results of statistical decomposition in empirical orthogonal functions (EOFs) are discussed. There is no evidence of an inter-hemispheric mode on the depth of the 20?°C-isotherm (D20) and heat content comparable to the observed mode for sea surface temperature (SST) fields. Most energetic patterns for D20 and heat content are dominated by the stronger variability in the northern part of the basin. Influences of other climate signals are investigated. Correlations between the winter NAO (North Atlantic Oscillation) index and our standard variables is marginally significant. A positive NAOW (North Atlantic Oscillation of Winter) is associated with SST cooling in a latitude band between 10°N and 20°N. When applied to the El-Niño index, correlations are much more significant. We found two scales of maximum correlation: at the four month lag after the El-Niño mature phase when the thermocline slope and zonal heat content gradient are maximum along the equator, and at the ten month lag after the mature phase of El-Niño when the thermocline slope weakens and the equatorial gradient of heat content vanished. The correlation with a zonal wind index (average between 30°W–35°W and 2°N–2°S) has been computed. Correlation is maximum at the six month lag when the thermocline slope and the zonal heat content gradient are maximum in the equatorial band. This “Atlantic Niño” mode is influenced by the Pacific Ocean's variability and reaches a maximum one year after a warm event in the eastern Pacific.  相似文献   

2.
Carried out is the statistical analysis of contemporary observed variations of air temperature and wind speed in the troposphere of the Northern Hemisphere based on the data on global surface air temperature for 1850–2013 obtained from the University of East Anglia Climate Research Unit (HadCRUT4) and NCEP/NCAR reanalysis (1948–2013). Revealed are the long-term trends of air temperature and wind speed at different constant-pressure levels. Established is the anticipatory role of the zonal atmospheric circulation in the long-term variability of air temperature in the lower troposphere averaged for the zone of 30°–70° N. According to the results of correlation analysis, in some areas of the Northern Hemisphere the contribution of the wind speed to air temperature variability makes up not less than 60%.  相似文献   

3.
The interannual variability in the formation of mini warm pool (MWP, SST ≥ 30.5°C) and its impact on the formation of onset vortex (OV) over the east-central Arabian Sea (ECAS) are addressed by analyzing the NCEP OIV 2-weekly SST data and NCEP–NCAR reanalysis 850 hPa wind fields from May to June (prior to the onset of monsoon) over the north Indian Ocean for a period of 12 years from 1992 to 2003. Strong interannual variability in the formation and intensification of MWP was observed. Further, the 850 hPa wind fields showed that OV developed into an intense system only during 1994, 1998 and 2001. It formed in the region north of the MWP and on the northern flank of the low-level jet axis, which approached the southern tip of India just prior to the onset of monsoon, similar to the vortex of MONEX-79. The area-averaged zonal kinetic energy (ZKE) over the ECAS (8–15°N, 65–75°E) as well as over the western Arabian Sea (WAS, 5°S–20°N, 50–70°E) showed a minimum value of 5–15 m2 s?2 prior to monsoon onset over Kerala (MOK), whereas a maximum value of 280 m2 s?2 (40–70 m2 s?2) was observed over the ECAS (WAS) during and after MOK. The study further examined the plausible reasons for the occurrence of MWP and OV.  相似文献   

4.
The spatial and temporal variability of rainfall over Ethiopia during the summer (JJAS) season is studied using observations (both station and satellite based) and model simulation data. The simulation dataset is generated using the fourth version of the International Center for Theoretical Physics Regional Climate Model (RegCM4) for the period 1989–2005. Ethiopia is first divided into 12 homogeneous regions using criteria including rotated empirical orthogonal function (REOF), spatial correlation, seasonal cycles, and topographical features. Spatially averaged observed and simulated rainfall time series are then generated and analyzed for each region. Standardized rainfall anomalies of the observations and the simulated data are highly correlated over the northern, western, northeastern, central, and southwestern regions, while a weak correlation is found over the border regions of the country. The dominant modes of rainfall variability are identified using REOF, while time–frequency variations of different dominant modes are described by wavelet analysis. The first leading patterns of rainfall and upper wind (averaged between 100 and 300 hPa) are highly correlated and exhibit similar features between simulation and observations over the northern, western, southwestern, and eastern regions of Ethiopia. The second loading pattern of rainfall and the first loading pattern of low-level wind (averaged between 850 and 1,000 hPa) exhibit a dipole structure across the southwestern and northeastern regions of the country. The dominant signals in the first rotated principal component (RPC) of rainfall and upper level wind fields show a period of 4–5 and 2–3 years, while the dominant signals in the second RPC show a period of 2–3 years at a 0.05 significance level. The correlations of significant RPCs across gauge, gridded, and model rainfall fields with that of low and upper level winds show the presence of a significant relationship (correlation exceeding ～0.6). Overall, the RegCM4 shows a good performance in simulating the spatial and temporal variability of precipitation over Ethiopia.  相似文献   

5.
To what extent is tropical variability forced from the North Pacific through ocean pathways relative to locally generated variability and variability forced through the atmosphere? To address this question, in this study we use an anomaly-coupled model, consisting of a global, atmospheric general circulation model and a 4½-layer, reduced-gravity, Pacific-Ocean model. Three solutions are obtained; with coupling over the entire basin (CNT), with coupling confined to the tropics and wind stress and heat fluxes in the North and South Pacific specified by climatology (TP), and with coupling confined to the Tropics and wind stress and heat fluxes in the North Pacific specified by output from CNT (NPF). It is found that there are two distinct signals forced in the North Pacific that can impact the tropics through ocean pathways. These two signals are forced by wind stress and surface heat flux anomalies in the subtropical North Pacific. The first signal is relatively fast, impacts tropical variability less than a year after forcing, is triggered from November to March, and propagates as a first-mode baroclinic Rossby wave. The second signal is only triggered during springtime when buoyancy forcing can effectively generate higher-order baroclinic modes through subduction anomalies into the permanent thermocline, and it reaches the equator 4–5 years after forcing. The slow signal is found to initiate tropical variability more efficiently than the fast signal with one standard deviation in subtropical zonal wind stress forcing tropical SST anomalies centered on the equator at 135°W of approximately 0.5°C. Allowing extratropically forced tropical variability is found to shift primarily 2-year ENSO variability in a tropics-alone simulation to a more realistic range of 2–6 years.  相似文献   

6.
The boreal summer intraseasonal oscillation (BSISO) of the Asian summer monsoon (ASM) is one of the most prominent sources of short-term climate variability in the global monsoon system. Compared with the related Madden-Julian Oscillation (MJO) it is more complex in nature, with prominent northward propagation and variability extending much further from the equator. In order to facilitate detection, monitoring and prediction of the BSISO we suggest two real-time indices: BSISO1 and BSISO2, based on multivariate empirical orthogonal function (MV-EOF) analysis of daily anomalies of outgoing longwave radiation (OLR) and zonal wind at 850 hPa (U850) in the region 10°S–40°N, 40°–160°E, for the extended boreal summer (May–October) season over the 30-year period 1981–2010. BSISO1 is defined by the first two principal components (PCs) of the MV-EOF analysis, which together represent the canonical northward propagating variability that often occurs in conjunction with the eastward MJO with quasi-oscillating periods of 30–60 days. BSISO2 is defined by the third and fourth PCs, which together mainly capture the northward/northwestward propagating variability with periods of 10–30 days during primarily the pre-monsoon and monsoon-onset season. The BSISO1 circulation cells are more Rossby wave like with a northwest to southeast slope, whereas the circulation associated with BSISO2 is more elongated and front-like with a southwest to northeast slope. BSISO2 is shown to modulate the timing of the onset of Indian and South China Sea monsoons. Together, the two BSISO indices are capable of describing a large fraction of the total intraseasonal variability in the ASM region, and better represent the northward and northwestward propagation than the real-time multivariate MJO (RMM) index of Wheeler and Hendon.  相似文献   

7.
Analyzed is the interannual variability of the meridional mass transport ψS in the North Atlantic based on the Sverdrup relation. The continuous (1980–2005) monthly wind stress dataset with the spatial resolution of 1 × 1° was used as the initial data. Sverdrup transport analysis performed for different latitudinal transects within the North Atlantic subtropical gyre demonstrated that the maximum long-term Sverdrup transport (?25.2 Sv) can be found at 33°N. Studied is a mechanism of the interaction between the meridional Sverdrup transport and the water flow in the Florida Strait. The significant correlation coefficient (0.5) is revealed for the Florida Strait water discharge and the mass transport at 27°N. Analyzed is the relationship between ψS and the North Atlantic Oscillation index and the statistically significant correlation coefficient (0.45) is obtained for the Sverdrup transport at 49°N.  相似文献   

8.
Wavelet analysis is applied to zonal mean zonal wind and temperature fields to represent characteristics of temporal periodic features different from the annual and semi-annual recurrence in the troposphere and stratosphere. A daily database of reanalyses is used for the period 1979–2008, which comprises the era of satellite-based data, as some discontinuities have been observed around 1978 in previous studies. Levels for this study have been chosen at 400 and 10 hPa, respectively in the middle troposphere and middle stratosphere. As representative for diverse latitudinal regions we have respectively selected 0°, ±20°, ±40°, ±60°, ±80°. Significant features were only found at the equator. The period of the quasi-biennial oscillation (QBO) is found to exhibit a decreasing trend in time over the 30 years studied. Potential harmonics of the QBO are found in the tropical stratosphere but also troposphere. However, they do not exhibit the same tendency. This fact supports in particular the idea that the QBO and the tropospheric biennial oscillation may be unrelated phenomena. Some of the observed features lie within the known range of variability of the El Niño Southern Oscillation. Faint effects of the 11-year solar cycle variability may have been observed in the troposphere and stratosphere, but no firm assertion may be made due to the low number of observed cycles for this kind of phenomenon in the used data-set time span. Short-term solar variabilities leave no relevant imprint.  相似文献   

9.
Interannual variability of both SW monsoon (June-September) and NE monsoon (October-December) rainfall over subdivisions of Coastal Andhra Pradesh, Rayalaseema and Tamil Nadu have been examined in relation to monthly zonal wind anomaly for 10 hPa, 30 hPa and 50 hPa at Balboa (9°N, 80°W) for the 29 year period (1958-1986). Correlations of zonal wind anomalies to SW monsoon rainfall (r = 0.57, significant at 1% level) is highest with the longer lead time (August of the previous year) at 10 hPa level suggesting some predictive value for Coastal Andhra Pradesh. The probabilities estimated from the contingency table reveal non-occurrence of flood during easterly wind anomalies and near non-occurrence of drought during westerly anomalies for August of the previous year at 10 hPa which provides information for forecasting of performance of SW monsoon over Coastal Andhra Pradesh. However, NE monsoon has a weak relationship with zonal wind anomalies of 10 hPa, 30 hPa and 50 hPa for Coastal Andhra Pradesh, Raya  相似文献   

10.
Using a large set of WRF ensemble simulations at 70-km horizontal resolution over a domain encompassing the Warm Pool region and its surroundings [45°N–45°S, 10°E–240°E], this study aims at quantifying how nudging techniques can modify the simulation of deep atmospheric convection. Both seasonal mean climate, transient variability at intraseasonal timescales, and the respective weight of internal (stochastic) and forced (reproducible) variability are considered. Sensitivity to a large variety of nudging settings (nudged variables and layers and nudging strength) and to the model physics (using 3 convective parameterizations) is addressed. Integrations are carried out during a 7-month season characterized by neutral background conditions and strong intraseasonal variability. Results show that (1) the model responds differently to the nudging from one parameterization to another. Biases are decreased by ~50 % for Betts–Miller–Janjic convection against 17 % only for Grell–Dévényi, the scheme producing yet the largest biases; (2) relaxing air temperature is the most efficient way to reduce biases, while nudging the wind increases most co-variability with daily observations; (3) the model’s internal variability is drastically reduced and mostly depends on the nudging strength and nudged variables; (4) interrupting the relaxation before the end of the simulations leads to an abrupt convergence towards the model’s natural solution, with no clear effects on the simulated climate after a few days. The usefulness and limitations of the approach are finally discussed through the example of the Madden–Julian Oscillation, that the model fails at simulating and that can be artificially and still imperfectly reproduced in relaxation experiments.  相似文献   

11.
Using the NCEP/NCAR reanalysis wind and temperature data (1948–2011) and India Meteorological Department (IMD) rainfall data, a long-term trend in the tropical easterly jet stream and its effect on Indian summer monsoon rainfall has been explained in the present study. A decreasing trend in zonal wind speed at 100 mb (maximum decrease), 150 mb, and 200 mb (minimum) is observed. The upper-level (100, 150, and 200 mb) zonal wind speed has been correlated with the surface air temperature anomaly index (ATAI) in the month of May, which is taken as the difference in temperature anomaly over land (22.5°N–27.5°N, 80°E–90°E) and Ocean (5°S–0°S, 75°E–85°E). Significant high correlation is observed between May ATAI and tropical easterly jet stream (TEJ) which suggests that the decreasing land–sea temperature contrast could be one major reason behind the decreasing trend in TEJ. The analysis of spatial distribution of rainfall over India shows a decreasing trend in rainfall over Jammu and Kashmir, Arunachal Pradesh, central Indian region, and western coast of India. Increasing trend in rainfall is observed over south peninsular and northeastern part of India. From the spatial correlation analysis of zonal wind with gridded rainfall, it is observed that the correlation of rainfall is found to be high with the TEJ speed over the regions where the decreasing trend in rainfall is observed. Similarly, from the analysis of spatial correlation between rainfall and May ATAI, positive spatial correlation is observed between May ATAI and summer monsoon rainfall over the regions such as south peninsular India where the rainfall trend is positive, and negative correlation is observed over the places such as Jammu and Kashmir where negative rainfall trend is observed. The decreased land–sea temperature contrast in the pre-monsoon month could be one major reason behind the decreased trend in TEJ as well as the observed spatial variation in the summer monsoon rainfall trend. Thus, the study explained the long-term trend in TEJ and its relation with May month temperature over the Indian Ocean and land region and its effect on the trend and spatial distribution of Indian summer monsoon rainfall.  相似文献   

12.
Abstract

Anemometer‐measured winds for the period 5–13 March 1994 were used to study the coherence of observed and forecast coastal winds along the mid‐Labrador shelf. The reliability of these variables in predicting the response of the ocean and ice to wind forcing is an important issue for ice forecasting in this area. Two anemometer‐equipped 2‐m ice beacons were deployed on pack ice north of Wolf Island and a third beacon was deployed on Grady Island. The results indicate that due to the influence of local topography, 10‐m winds observed at the meteorological station in Cartwright, Labrador provide a poor estimate (r2 = 0.2) of wind conditions over the offshore sea‐ice. In contrast, the σ = 1 level (～10 m) winds from the Canadian Meteorological Centre's Regional Finite Element (RFE) model provided a better correlation with anemometer beacon winds (0.90 for the 6‐hour forecast down to 0.45 at 36 hours). However, the RFE model overestimates the magnitude of the winds by 10–40%.

The response of the ocean and ice cover to wind forcing was measured by an ocean bottom‐mounted acoustic Doppler current proþler (ADCP). Relative to the 2‐m beacon winds, the ice moved at 2.5% of wind magnitude and turned 0.6° to the left of the wind. The ocean response decreased with depth until it reached a constant value of 0.9% of the wind speed. The turning angle increased from 0.3° to the right of the wind at 3.5 m to 50° at the lowest level measured by the ADCP (73 m depth). Approximately 57% of the variance in the ocean currents at 3 m below the surface can be attributed to the 2‐m winds; at 73 m the explained variance decreases to 27%.  相似文献   

13.
相关方法分析Nino3区SSTA和风应力的关系，发现前期风应力距平场与Nino3区SSTA有很好的相关关系，这种相关性超前8个月时就有所显现。影响Nino3区SSTA的主要风应力区域的位置随风应力超前的时间缩短均向中太平洋扩展。数值试验方法研究不同区域的风应力对热带太平洋SST作用的结果表明，强相关区域的风应力对形成和维持热带太平洋SST的气候场的作用不明显，而对SST的年际变率有重要贡献；相反，强相关区域以外的风应力对形成和维持热带太平洋SST的气候场起重要作用，但是对SST的年际变率所起的作用很不理想。  相似文献   

14.
The western North Pacific subtropical high (WNPSH) is a crucial component of the East Asian summer monsoon (EASM) system and significantly influences the precipitation in East Asia. In this study, distinguished role of WNPSH on the EASM and Indian Ocean monsoon (IOM) are investigated. Based on the boreal summer mean field of 850-hPa geopotential height and its interannual variability, the WNPSH index (WNPSHI) is defined by the areaaveraged geopotential height over the region [110°–150°E, 15°–30°N]. The WNPSHI is significantly related to the precipitation over the East Asian monsoon (EAM) region [105°–150°E, 30°–40°N] and IOM region [70°–105°E, 5°–15°N]. Rainfalls over these two regions have good correlation with WNPSH developments and the geopotential height fields at 850 hPa related to the EAM precipitation and IOM precipitation have remarkably different teleconnection patterns in boreal summer. These features exhibit that EAM and IOM precipitations have different type of development processes associated with different type of WNPSH each other. Focusing on the relationships among the EAM precipitation, IOM precipitation, and the WNPSH variabilities, we assume that WNPSH and EAM precipitation are usually fluctuated simultaneously through the sea surface temperature (SST)-subtropical ridge-monsoon rainfall feedback, whereas the IOM precipitation varies through the different process. To clarify the relationships among WNPSH, EAM, and IOM, two cases are selected. The first one is the case that all of WNPSH, EAM, and IOM are in phase (WE(+)I(+)), and the second one is the case that WNPSH and EAM are in phase and WNPSH/EAM and IOM is out of phase (WE(+)I(?)). These two cases are connected to the thermal forcing associated with SST anomalies over the eastern Pacific and Indian Ocean. This different thermal forcing induces the change in circulation fields, and then anomalous circulation fields influence the moisture convergence over Asian monsoon regions interactively. Therefore, the monsoon rainfall may be changed according to the thermal conditions over the tropics.  相似文献   

15.
Direct air-sea flux measurements were made on R/V Kexue #1 at 4 ° S, 156 ° E during the Tropical Ocean Global Atmosphere (TOGA) Coupled Ocean-Atmospheric Response Experiment (COARE) Intensive Observation Period (IOP). An array of six accelerometers was used to measure the motion of the anchored ship, and a sonic anemometer and Lyman-α hygrometer were used to measure the turbulent wind vector and specific humidity. The contamination of the turbulent wind components by ship motion was largely removed by an improvement of a procedure due to Shao based on the acceleration signals. The scheme of the wind correction for ship motion is briefly outlined. Results are presented from data for the best wind direction relative to the ship to minimize flow distortion effects. Both the time series and the power spectra of the sonic-measured wind components show swell-induced ship motion contamination, which is largely removed by the accelerometer correction scheme. There was less contamination in the longitudinal wind component than in the vertical and transverse components. The spectral characteristics of the surface-layer turbulence properties are compared with those from previous land and ocean results. Momentum and latent heat fluxes were calculated by eddy correlation and compared to those estimated by the inertial dissipation method and the TOGA COARE bulk formula. The estimations of wind stress determined by eddy correlation are smaller than those from the TOGA COARE bulk formula, especially for higher wind speeds, while those from the bulk formula and inertial dissipation technique are generally in agreement. The estimations of latent heat flux from the three different methods are in reasonable agreement. The effect of the correction for ship motion on latent heat fluxes is not as large as on momentum fluxes.  相似文献   

16.
In the present study, interannual fluctuations of the mixed layer depth (MLD) in the tropical Indian Ocean are investigated from a long-term (1960–2007) eddy permitting numerical simulation and a new observational dataset built from hydrographic in situ data including Argo data (1969–2008). Both datasets show similar interannual variability patterns in relation with known climate modes and reasonable phase agreement in key regions. Due to the scarcity of the observational dataset, we then largely rely on the model to describe the interannual MLD variations in more detail. MLD interannual variability is two to four times smaller than the seasonal cycle. A large fraction of MLD interannual variations is linked to large-scale climate modes, with the exception of coastal and subtropical regions where interannual signature of small-scale structures dominates. The Indian Ocean Dipole is responsible for most variations in the 10°N–10°S band, with positive phases being associated with a shallow MLD in the equatorial and south-eastern Indian Ocean and a deepening in the south-central Indian Ocean. The El Niño signature is rather weak, with moderate MLD shoaling in autumn in the eastern Arabian Sea. Stronger than usual monsoon jets are only associated with a very modest MLD deepening in the southern Arabian Sea in summer. Finally, positive Indian Ocean Subtropical Dipoles are associated with a MLD deepening between 15 and 30°S. Buoyancy fluxes generally appear to dominate MLD interannual variations except for IOD-induced signals in the south-central Indian Ocean in autumn, where wind stirring and Ekman pumping dominate.  相似文献   

17.
Spatial and temporal structures of interannual-to-decadal variability in the tropical Pacific Ocean are investigated using results from a global atmosphere–ocean coupled general circulation model. The model produces quite realistic mean state characteristics, despite a sea surface temperature cold bias and a thermocline that is shallower than observations in the western Pacific. The periodicity and spatial patterns of the modelled El Niño Southern Oscillations (ENSO) compare well with those observed over the last 100 years, although the quasi-biennial timescale is dominant. Lag-regression analysis between the mean zonal wind stress and the 20°C isotherm depth suggests that the recently proposed recharge-oscillator paradigm is operating in the model. Decadal thermocline variability is characterized by enhanced variance over the western tropical South Pacific (~7°S). The associated subsurface temperature variability is primarily due to adiabatic displacements of the thermocline as a whole, arising from Ekman pumping anomalies located in the central Pacific, south of the equator. Related wind anomalies appear to be caused by SST anomalies in the eastern equatorial Pacific. This quasi-decadal variability has a timescale between 8 years and 20 years. The relationship between this decadal tropical mode and the low-frequency modulation of ENSO variance is also discussed. Results question the commonly accepted hypothesis that the low-frequency modulation of ENSO is due to decadal changes of the mean state characteristics.  相似文献   

18.
Four regions are detected in northern Africa (20° W–40° E, 0–30° N) by applying the cluster analysis method on the annual rainfall anomalies of the period 1901–2000. The first region (R1), an arid land, covers essentially the north of 17.75° N from west to east of the study zone. The second region (R2), a semiarid land with a Sahelian climate, less warm than the dry climate of R1, is centred on Chad, with almost regular extension to the west towards Mauritania, and to the east, including the north of the Central African Republic and the Sudan. The region 3 (R3), a wet land, is centred on the Ivory Coast and covers totally Liberia, the south part of Ghana, Togo, Benin and the southwest of Nigeria. The fourth region (R4), corresponding to the wet equatorial forest, covers a part of Senegal, the Central Africa, the south of Sudan and a part of Ethiopia. An analysis of observed temperature and precipitation variability and trends throughout the twentieth century over these regions is presented. Summer, winter and annual data are examined using a range of variability measures. Statistically, significant warming trends are found over the majority of regions. The trends have a magnitude of up to 1.5 K per century. Only a few precipitation trends are statistically significant. Regional temperature and precipitation show pronounced variability at scales from interannual to multi-decadal. The interannual variability shows significant variations and trends throughout the century, the latter being mostly negative for precipitation and both positive and negative for temperature. Temperature and precipitation anomalies show a chaotic-type behaviour in which the regional conditions oscillate around the long-term mean trend and occasionally fall into long-lasting (up to 10 years or more) anomaly regimes. A generally modest temporal correlation is found between anomalies of different regions and between temperature and precipitation anomalies for the same region. This correlation is mostly positive for temperature in cases of adjacent regions. Several cases of negative interregional precipitation anomaly correlation are found. The El Niño Southern Oscillation significantly affects the anomaly variability patterns over a number of regions, mainly regions 3 (R3) and 4 (R4), while the North Atlantic Oscillation significantly affects the variability over arid and semiarid regions, R1 and R2.  相似文献   

19.
The diurnal and semidiurnal tidal wind field variations in the altitudes between 80 and 100 km of the earth’s atmosphere over a mid-latitude station are studied by means of the phases of the zonal and meridional wind measurements made at Atlanta (34oN, 84oW). The rotation of diurnal tidal wind vector is seen to be clockwise at lower heights (80-86 km), swinging between clockwise and unti-clockwise at intermediate heights (88-96 km) and anti-clockwise at higher-heights (96- 100 km). The senses of rotation of diurnal and semidiurnal tidal wind vectors are compared between the stations located in the same and opposite hemispheres. The results are consistent with the tidal theory in the case of Atlanta and Adelaide (35oS, 139oE) whereas in the case of other stations considered in the present study, they showed marked variations.  相似文献   

20.
High-resolution sea wind hindcasts over the Mediterranean area   总被引：1，自引：1，他引：0  
The goal of this study is to develop a high-resolution atmospheric hindcast over the Mediterranean area using the WRF-ARW model, focusing on offshore surface wind fields. In order to choose the most adequate model configuration, the study provides details on the calibration of the experimental saet-up through a sensitivity test considering the October–December 2001 period (the 2001 super-storm event in the West Mediterranean). A daily forecast outperforms the spectral technique of previous products and the boundary data from ERA-Interim reanalysis produces the most accurate estimates in terms of wind variability and hour-to-hour correspondence. According to the sensitivity test, two data sets of wind hindcast are produced: the SeaWind I (30-km horizontal resolution for a period of 60 years) and the SeaWind II (15-km horizontal resolution for 20 years). The validation of the resulting surface winds is undertaken considering two offshore observational datasets. On the one hand, hourly surface buoy stations are used to validate wind time series at specific locations; on the other hand, wind altimeter satellite observations are considered for spatial validation in the whole Mediterranean Sea. The results obtained from this validation process show a very good agreement with observations for the southern Europe region. Finally, SeaWind I and II are used to characterize offshore wind fields in the Mediterranean Sea. The statistical structure of sea surface wind is analyzed and the agreement with Weibull probability distribution is discussed. In addition, wind persistence and extreme wind speed (50 year return period) are characterized and relevant areas of wind power generation are described by estimating wind energy quantities.  相似文献   

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