ECMWF Wind Data Research Articles

Persian Gulf zone classification based on the wind and wave climate variability

This study aims to assess the wind and wave spatio-temporal variability in the Persian Gulf using localized ECMWF wind data and numerically modeled wave characteristics in a 31-yearly period. The results represented that the highest values occur mainly in the middle part of the domain, especially during the winter, and the seasonal variation of the wind and wave climate is mostly affected by Shamal wind phenomena while the winter and summer-time Shamal winds affect the middle and northwestern parts of the Persian Gulf, respectively. For quantitative assessment, twenty stations were selected and the results indicated that the highest mean significant wave height (SWH) occurs in the central strip of the middle parts of the Persian Gulf during both February and June, while the monthly variations of wind and wave characteristics are different in the stations located near the Strait-of-Hormuz. In addition, the temporal stability of both wind speed (WS) and SWH is more in the eastern part of the domain, while the stability of wave dominant direction is more than that of wind. Based on the similarity between the temporal variations of wind and wave characteristics, the domain was divided into three sub-regions as representatives of different wind/wave climates.

Airborne Wind Lidar Measurements of Vertical and Horizontal Winds for the Investigation of Orographically Induced Gravity Waves

AbstractAirborne coherent Doppler wind lidar measurements, acquired during the Gravity Wave Life-Cycle (GW-LCYCLE) I field campaign performed from 2 to 14 December 2013 in Kiruna, Sweden, are used to investigate internal gravity waves (GWs) induced by flow across the Scandinavian Mountains. Vertical wind speed is derived from lidar measurements with a mean bias of less than 0.05 m s−1 and a standard deviation of 0.2 m s−1 by correcting horizontal wind projections onto the line-of-sight direction by means of ECMWF wind data. The horizontal wind speed and direction are retrieved from lidar measurements by applying a velocity–azimuth display scan and a spectral accumulation technique, leading to a horizontal resolution of about 9 km along the flight track and a vertical resolution of 100 m, respectively. Both vertical and horizontal wind measurements are valuable for characterizing GW properties as demonstrated by means of a flight performed on 13 December 2013 acquired during weather conditions favorable for orographic GW excitation. Wavelet power spectra of the vertical wind speed indicate that the horizontal GW wavelengths lay mainly between 10 and 30 km and that the GW amplitude above the mountain ridge decreases with increasing altitude. Additionally, the perturbations of the horizontal wind speed are analyzed, showing horizontal wavelengths in the excitation region of 100–125 km with upwind-tilted wave fronts. By means of elevation power spectra, it is revealed that vertical wind power spectra are dominated by the short-wave elevation part, whereas horizontal wind perturbations are dominated by the long-wave part.

Lightning activity and its relationship with typhoon intensity and vertical wind shear for Super Typhoon Haiyan (1330)

Super Typhoon Haiyan (1330), which occurred in 2013, is the most powerful typhoon during landfall in the meteorological record. In this study, the temporal and spatial distributions of lightning activity of Haiyan were analyzed by using the lightning data from the World Wide Lightning Location Network, typhoon intensity and position data from the China Meteorological Administration, and horizontal wind data from the ECMWF. Three distinct regions were identified in the spatial distribution of daily average lightning density, with the maxima in the inner core and the minima in the inner rainband. The lightning density in the intensifying stage of Haiyan was greater than that in its weakening stage. During the time when the typhoon intensity measured with maximum sustained wind speed was between 32.7 and 41.4 ms−1, the storm had the largest lightning density in the inner core, compared with other intensity stages. In contrast to earlier typhoon studies, the eyewall lightning burst out three times. The first two eyewall lightning outbreaks occurred during the period of rapid intensification and before the maximum intensity of the storm, suggesting that the eyewall lightning activity could be used to identify the change in tropical cyclone intensity. The flashes frequently occurred in the inner core, and in the outer rainbands with the black body temperature below 220 K. Combined with the ECMWF wind data, the influences of vertical wind shear (VWS) on the azimuthal distribution of flashes were also analyzed, showing that strong VWS produced downshear left asymmetry of lightning activity in the inner core and downshear right asymmetry in the rainbands.

Rainfall mechanism over the rain-shadow region of north peninsular India

Rainfall mechanism over the rain-shadow region of north peninsular India during the summer monsoon season has been investigated using dynamic, thermodynamic, cloud microphysics and cloud dynamic (CMCD) forcings. Daily rainfall data has been used to understand rainfall variability. Daily ECMWF wind data for the period 2009–2011 have been used to study the wind divergence, shear and vertical velocity profiles. Daily thermodynamic parameters from upper air soundings of Hyderabad (17.448°N, 78.381°E), have been examined. Aircraft data have been used to study CMCD parameters. The divergence is found between surfaces to 850 hPa level whereas the convergence is at 850 hPa, which comes down to surface level during presence of low pressure systems. The divergence is observed at low (700 hPa), mid (600–300 hPa) and upper (250–150 hPa) tropospheric levels. In consequence of these divergence structures, three types of cloud systems viz. shallow, congestus and deep are developed with bases just above 850 hPa and tops at corresponding three divergent levels. The vertical profiles of relative humidity observed by radiosonde data have been analyzed to get the frequency distribution of shallow, congestus and deep clouds. The highest frequency observed is that of congestus clouds. The thermodynamic structure shows dry surface level and warm and moist middle troposphere with tongues of dry air and multilevel inversions which have been attributed to advection of aerosol-rich dry air. The aircraft observations showed high aerosol concentrations from surface to 5 km, polluted clouds with cloud droplet effective radius smaller than that required for collision–coalescence process. The factors which are responsible for causing low rainfall over the rain-shadow area have been identified.

A COMPARATIVE STUDY ON WIND AND WAVE SOURCES FOR TURKISH BLACK SEA COAST

With this study, considering two study sites at Black Sea coast of Turkey where in-situ wind measurements are available, it is planned to reveal the necessary steps that should be followed for the alternative wind and wave resource, ECMWF, that can be used for research and engineering purposes. The study involves comparing 6 hourly ECMWF wind data with in-situ wind measurements in terms of speed and direction, finding correlation between these two data sets, modifying the ECMWF wind data, wave modeling with W61 or SWAN or both in which the modified ECMWF wind data will be used as input, comparing the obtained wave data with in-situ wave measurements and comparing the in-situ wave measurements with ECMWF wave data and with obtained wave data. During these studies, it will be necessary to obtain hourly ECMWF wind data from 6 hourly ECMWF wind data with searching several best-fitting methods and using Matlab toolboxes for his study.

Error distribution and correction of the predicted wave characteristics over the Persian Gulf

Wind-waves are the most important environmental parameter for the design of coastal and offshore structures, sediment transport, coastal erosion etc. Therefore, an accurate evaluation of the wave climate is of great importance. Due to the lack of long term measurements, nowadays numerically modeled wave data are widely used for determining the wave climate. The numerically simulated wave data are continuous in time and space, but generally inaccurate in enclosed and semi-enclosed basins mainly due to the inaccurate wind input data. The main goal of this study is to develop a new and efficient approach to improve the hindcasted wave parameters in the Persian Gulf. Hence, the third generation SWAN model was employed for the wave modeling forced by the 6-hourly ECMWF wind data with a resolution of 0.5°. A new methodology was introduced for the distribution of wave prediction errors from discrete observation points to the other points of interest. It was found that the proposed method which considers the wave generation physics, leads to a significant improvement in the predicted wave parameters. In addition, it was revealed that the improvements in prediction of waves with higher wave heights and longer periods are more than those of others. This was shown to be due to the higher correlation between high values of output parameters which contain larger errors. The influence radius in the error distribution procedure was found to be near 2° (~200km).

Flux calculation using CARIBIC DOAS aircraft measurements: SO2 emission of Norilsk

Based on a case‐study of the nickel smelter in Norilsk (Siberia), the retrieval of trace gas fluxes using airborne remote sensing is discussed. A DOAS system onboard an Airbus 340 detected large amounts of SO2 and NO2 near Norilsk during a regular passenger flight within the CARIBIC project. The remote sensing data were combined with ECMWF wind data to estimate the SO2 output of the Norilsk industrial complex to be around 1 Mt per year, which is in agreement with independent estimates. This value is compared to results using data from satellite remote sensing (GOME, OMI). The validity of the assumptions underlying our estimate is discussed, including the adaptation of this method to other gases and sources like the NO2 emissions of large industries or cities.

Wave data assimilation using a hybrid approach in the Persian Gulf

The main goal of this study is to develop an efficient approach for the assimilation of the hindcasted wave parameters in the Persian Gulf. Hence, the third generation SWAN model was employed for wave modeling forced by the 6-h ECMWF wind data with a resolution of 0.5°. In situ wave measurements at two stations were utilized to evaluate the assimilation approaches. It was found that since the model errors are not the same for wave height and period, adaptation of model parameter does not result in simultaneous and comprehensive improvement of them. Therefore, an approach based on the error prediction and updating of output variables was employed to modify wave height and period. In this approach, artificial neural networks (ANNs) were used to estimate the deviations between the simulated and measured wave parameters. The results showed that updating of output variables leads to significant improvement in a wide range of the predicted wave characteristics. It was revealed that the best input parameters for error prediction networks are mean wind speed, mean wind direction, wind duration, and the wave parameters. In addition, combination of the ANN estimated error with numerically modeled wave parameters leads to further improvement in the predicted wave parameters in contrast to direct estimation of the parameters by ANN.

Airborne multi-axis DOAS measurements of tropospheric SO<sub>2</sub> plumes in the Po-valley, Italy

Abstract. During the second FORMAT (FORMaldehyde as A Tracer of oxidation in the troposphere) campaign in 2003 the airborne multi-axis DOAS instrument (AMAXDOAS) performed scattered-light spectroscopic measurements of SO2 over the city of Mantova and the power plant Porto Tolle, both situated in the Po-valley, Northern Italy. The SO2 vertical columns and emission flux were derived from two days of measurements, 26 and 27 September 2003. The SO2 emission flux from the power plant Porto Tolle was calculated to 1.93×1025 molec s-1 on 26 September and in good agreement with official emission data, which quote 2.25×1025 molec s-1. On 27 September the measured flux was much lower (3.77×1024 molec s-1) if ECMWF wind data are used, but of comparable magnitude (2.4×1025 molec s-1) if the aircraft on-board wind measurements are utilised. Official emission data was 2.07×1025 molec s-1 indicating only a small change from the previous day. Over the city of Mantova, the observed SO2 vertical columns were 1.1×1016 molec cm-2 and 1.9×1016 molec cm-2 on 26 and 27 September, respectively. This is in good agreement with ground-based measurements of 5.9 ppbv and 10.0 ppbv which correspond to 1.2×1016 molec cm-2 and 2.2×1016 molec cm-2 if a well mixed boundary layer of 500m altitude is assumed.

Sensitivity of Coastal Currents near Point Conception to Forcing by Three Different Winds: ECMWF, COAMPS, and Blended SSM/I–ECMWF–Buoy Winds

Abstract Previous observational and modeling studies have indicated the importance of finescale winds in determining the circulation near Point Conception in the Santa Maria Basin (SMB) and the Santa Barbara Channel (SBC), California. There has not been a systematic attempt, however, to analyze and quantify the sensitivity of the near-surface circulation to different wind data. Here, a regional circulation model of the SMB and SBC is driven using three wind datasets: the European Centre for Medium-Range Weather Forecasts (ECMWF; ≈ 110 km × 110 km horizontal grid), the Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS; 9 km × 9 km horizontal grid), and a blended wind product that combines Special Sensor Microwave Imager (SSM/I), ECMWF, and buoy and coastal wind data and that is referred to as SEB. A springtime period (March–May 1999) in which equatorward wind dominates and wind stress curls are strong is chosen for the study. Two groups of experiments are conducted: with and without assimilating moored temperature observations. The focus is on long time scales of greater than weeks and on mean currents. Comparisons between these experiments and between model and observation show that the circulation driven by the ECMWF wind is much weaker than that by the other two winds. On the other hand, the SEB dataset shows locally intensified wind stress curls behind capes and coastal bends, whereas these wind stress curls are weak in COAMPS. It is found that these small-scale variations in the wind field force alongshore inhomogeneous pressure gradients that in turn can significantly affect the near-coast currents. The result is that modeled currents forced by SEB agree better with observations than do those produced by COAMPS. Empirical orthogonal function analyses were conducted on the near-surface currents, sea level, wind, and wind stress curl. The mode-1 current (≈40%) is unidirectional (i.e., generally equatorward or poleward) and correlates well with the mode-1 wind (≈90%). The mode-2 current (≈20%) is cyclonic in the SBC and poleward inshore and equatorward offshore in the SMB; it correlates well with mode-1 sea level (≈70%), which suggests that mode-2 currents are driven by the pressure gradient. It is significant that neither mode-2 current nor mode-1 sea level correlates well with mode-1 wind stress curl (≈70%); rather, they correlate well with the time integral of the mode-1 wind stress curl. These conclusions support a previous theoretical idea that cyclonic circulation in the SBC and the inshore currents of the SMB are both driven by alongshore pressure setup induced by the time integral of the wind stress curl, rather than by the wind stress curl itself. This idea of a pressure setup is consistent with the differences found between the currents driven by COAMPS and SEB winds.

To what extent can the 2002 Antarctic major stratospheric warming be explained by horizontal advection of the vortex from the pole?

The importance of horizontal and vertical advection of temperature for the Antarctic major stratospheric warming in September 2002 has been investigated, by applying the thermodynamic energy equation to ECMWF temperature and wind data. The analysis, which is carried out for the one-week period 19–26 September, shows that the large temperature increase in this period in the polar stratosphere is mainly due to horizontal advection of temperature. In addition, it has been investigated to what extent the observed temperature increase, as well as the change in the zonal wind, can be simulated with a simple conceptual model of a moving polar vortex. The model consists of a horizontal, circular vortex whose centre moves with constant meridional velocity off from the South Pole. The temperature and zonal wind fields are prescribed, stationary and zonally symmetric (relative to the vortex centre). Despite its simplicity, the model simulates several important aspects of the observations, such as the zonal-mean temperature increase and zonal-mean zonal wind reversal poleward of 60° S, and the zonal-mean temperature decrease at middle latitudes.

A Lagrangian computation of stratosphere–troposphere exchange in a tropopause-folding event in the subtropical Southern Hemisphere

A new Lagrangian technique to calculate the air mass flux across potential vorticity (Q) surfaceshas been used to perform a case study of a tropopause-folding event in the subtropical SouthernHemisphere. The flux is computed from the rate of change in Q along trajectories, which arecalculated from ECMWF wind data. Because the tropopause can be defined as a Q surface, the method can be used for the calculation of stratosphere–troposphere exchange (STE). Alarge number of forward and backward trajectories were calculated, starting in the vicinity ofthe tropopause fold. This fold was observed during the TRACAS (TRAnsport of Chemicalspecies Across the Subtropical tropopause) experiment at La Reunion (21°S, 55°E) in July 1998.With the Lagrangian method the cross tropopause air mass flux can be calculated for thedifferent tropopause levels, that occur in case of a tropopause folding. The computed massexchange is about — 20×1013 kg (i.e., downward) in 4.5 days, which is rather small comparedto other (midlatitude) mass exchange studies. The ratio of the fluxes per unit of area in andoutside of the fold is about 200 : 1. An indication of the accuracy of the calculated fluxes hasbeen obtained with the help of the ozone soundings made during the TRACAS experiment.

An ecological-physical coupled model applied to Station Papa

A vertical one-dimensional ecosystem model was constructed and applied to Station Papa. The model has seven compartments (phytoplankton, nitrate, ammonium, zooplankton, particulate organic matters, dissolved organic matters, dissolved oxygen) and was coupled with a mixed layer model for calculating diffusion coefficient which appears in the governing equations. The mixed layer model was driven by SST, SSS data observed at Station Papa in 1980 and ECMWF wind data for 1980, and the ecosystem model was driven by fixing nitrate concentration in deep layer to an observational value. The phytoplankton maximum in March was reproduced by the model although the maximum in fall-winter could not be reproduced. The model also suggests the importance of studying nitrification. As a whole, the model could reproduce characteristic features at Station Papa such as the summer ammonium maximum at 50 m depth, the summer dissolved oxygen maximum at 70 m depth and the absence of remarkable phytoplankton bloom.

A Qualitative Assessment of the Australian Tropical Region Analyses

The Bureau of Meteorology, Australia, routinely analyzes the tropospheric winds over the Australian Tropical Region (40°S–40°N, 70°–180°E). These wind data are assimilated without the use of a forecast model. While being free of any model bias, the optimum interpolation scheme imposes no dynamical constraints on the winds. To assess the realism of the Australian Tropical Region analyses, a qualitative comparison with gridded ECMWF wind data and OLR (as a proxy for tropical convection) is conducted. In general, the depiction of the large-scale tropical circulation of the Australian Tropical Region analyses is quite reasonable. The gross features of the Australian and Asian Monsoons seem equally captured by both the ECMWF and Australian analyses. The seasonal development of the two monsoons and the relationship between the vertical structure of the divergence and zonal wind depicted in the Australian analyses agree well with previous theoretical and observational studies. Subtle differences (such as with the phase of the upper level anticyclones relative to the divergence) between the theory and the dynamics inferred from the Australian analyses are highlighted. However, we conclude that these objectively analyzed tropospheric winds are a valuable data resource for both the comparison with forecast model assimilated data and for deduction of physical processes.