Wind Speed Field Research Articles

World ocean mean monthly waves, swell, and surface winds for July through October 1978 from SEASAT radar altimeter data

Abstract Data acquired by the SEASAT radar altimeter during the satellite's three‐month lifetime are used to obtain mean monthly maps of significant wave height, minimum swell, and surface wind speed for the world oceans. The SEASAT lifetime 26 June to 10 October 1978, corresponds to the Arctic summer and Antarctic winter. Thus, the highest sea states as derived from the radar altimeter data occur in the high latitudes of the Southern Ocean, reaching the mean monthly extreme magnitudes of 6‐m significant wave height, 5‐m minimum swell amplitude, and 12 m/s surface wind speed. Several features of the wave and wind fields agree with conventional descriptions. For example, the principal zonal wind regimes of the westerlies and trade winds and the doldrums and monsoon region are clearly evident in the monthly averages. Significant wave height and swell, whose mean fields always appear to be smoother than the mean wind speed fields, exhibit minima near the doldrums and steady increases southward and northward ...

On the location of the source for the energetic electron layer at the polar magnetopause and its relation to magnetic reconnection

The existence of a layer of energetic (≳20 keV) electrons along the magnetopause, extending from the polar cusp region to the distant magnetotail, has been established by measurements on various spacecraft. We have performed a statistical study of electron flux and spectral measurements above 0.5 MeV observed in different regions of the magnetopause accessible to HEOS 2, with the aim of identifying the source for this magnetopause electron layer. The measurements along the polar magnetotail (i.e., adjacent to the plasma mantle), along the mid‐latitude dayside magnetopause (i.e., adjacent to the dayside plasma boundary layer), and on both sides of the magnetosheath/polar cusp interface (i.e., in the exterior polar cusp and in the entry layer) have been separately analyzed and are statistically compared. We conclude that escape of electrons from the magnetosphere can be excluded as a significant source for the tail magnetopause layer on the basis of the observed intensities, of the spectra, and of the frequency of appearance of electrons outside those magnetopause regions which lie adjacent to the outer trapping zone. The electron intensities in the exterior polar cusp region are found to be correlated with the north/south component of the interplanetary magnetic field (IMF). High intensity levels are observed when the IMF is directed southward (BZ <0), and low levels when the IMF points northward (BZ >0). The electron flux in the exterior cusp region at times of southward IMF and at the near‐earth polar magnetotail at times of northward IMF is well correlated with the number of field lines carried by the solar wind towards the magnetosphere (expressed by the product of solar wind speed and interplanetary field magnitude). We interpret this as strong evidence that acceleration processes associated with magnetic reconnection occur at the magnetopause at those times. Local acceleration near the high‐latitude magnetopause appears therefore to be a prime source for the magnetopause electron layer.

Dependence of mid‐latitude hydromagnetic energy spectra on solar wind speed and interplanetary magnetic field direction

Relationships are examined between interplanetary parameters and local daytime geomagnetic energy (at Pittsburg, New Hampshire; L ∼3.5) in three period bands. Ground‐based magnetometer data, for 336 hours during July and August 1975, are studied when good interplanetary data coverage was available from instruments on the Imp J spacecraft. Multiple linear regression analyses show that the most important interplanetary parameter controlling ground hourly magnetic energy (in the period range 60–240 s) is the solar wind speed. Multiple linear regression analyses further show that hourly magnetic energy in the 30‐ to 60‐s period range is controlled by the solar wind speed and the interplanetary magnetic field direction. The velocity dependence supports the idea of wave production at the magnetopause via the Kelvin‐Helmholtz instability. These waves are later observed as magnetic pulsations (30–240 s) on the ground. The interplanetary magnetic field direction dependence supports the idea that waves produced at or near the earth's bow shock are later observed on the ground as magnetic pulsations in the shortest period band (30–60 s).

Hurricane Wind Speeds in the United States

A Monte Carlo simulation technique is used to obtain estimates of hurricane wind speeds along the Gulf and East Coasts of the United States. The paper describes the sources of data, the probabilistic models for climatological characteristics of hurricanes, and the physical models for the hurricane wind speed field used in the estimations. Estimated values of fastest-mile hurricane wind speeds at 10 m above ground in open terrain at the coastline and at 200 km inland are given for various mean recurrence intervals. The estimated hurricane wind speeds were found to be best fitted by Weibull distributions with tail length parameters γ≥4. Estimates are given of various errors inherent in the estimated values of the hurricane wind speeds. Owing to uncertainties with respect to the applicability of the physical models used in this work to locations north of Cape Hatteras, estimated hurricane wind speeds given for these locations should be viewed with caution.

Spectral analysis of wind speed and atmospheric electric field near ground

Spectral analysis of wind speed and atmospheric electric field near ground

Spectral analysis of wind speed and atmospheric electric field near ground

Spectra and cospectra of wind speed and atmospheric electric field (AEF) near ground measured at Trino Vercellese (Po Valley), during March 1973, are presented and discussed. Correlations between AEF and meteorological parameters were studied under conditions of fair and disturbed weather in order to identify the influence of weather conditions on the relationships between air turbulence and AEF. Results show that the correlation between air turbulence and AEF is best under fair weather conditions, but also that all the types of weather should be investigated for a clear understanding of the interrelations between the two phenomena. Finally a few tentative explanations are advanced for a few peculiar peaks shown by our spectra.

On the use of wind direction fieid for the estimation of wind speed field

This paper describes an objective scheme to estimate wind speed from the available isogonal field in the interior region and wind speed and direction for the boundary region. As a first step, the mean monthly wind field is taken as a guess field for the interior region. The divergence field is then computed, which along with the wind direction for the interior region is used to improve the guess field in successive scans, so as to match it with a the wind field along the boundary.
 This method has been tested over central India, a region of good conventional network. The results of the scheme which has potential advantages for augmenting data in otherwise sparse data region, is discussed.

Objective Sea-Level Pressure Analysis for Data-Sparse Areas

A computer procedure, described in an earlier study, uses the wind speed field near the ocean surface in combination with a small number of observations of pressure and wind velocity to specify the maritime sea-level pressure field. An improved version was used to analyze the pressure distribution over the North Pacific Ocean for eleven synoptic times in February 1967. Independent knowledge of the central pressures of lows is shown to reduce the analysis errors for very sparse data coverage. The application of planned remote sensing of sea-level wind speeds is shown to make a significant contribution to the quality of the analysis especially in the high gradient midlatitudes and for sparse coverage of conventional observations (such as over Southern Hemisphere oceans). Uniform distribution of the available observations of sea-level pressure and wind velocity yields results far superior to those derived from a random distribution.

Project Jet Stream Research Flight No. 30, April 1957

AbstractAn analysis is made of Project Jet Stream Research Flight No. 30, conducted on 8 April 1957. This flight made several traverses through a pronounced jet stream over the New England States. The fields of wind speed, potential temperature, vorticity and divergence are presented in vertical cross‐sections. Special reference is made to the differences between geostrophic and actual vertical wind shear in the vicinity of the jet core.