Onboard Wind Research Articles

Lagrangian Coherent Structure Analysis of Terminal Winds Detected by Lidar. Part II: Structure Evolution and Comparison with Flight Data

AbstractUsing observational data from coherent Doppler light detection and ranging (lidar) systems situated at the Hong Kong International Airport (HKIA), the authors extract Lagrangian coherent structures (LCS) intersecting the flight path of landing aircraft. They study the time evolution of LCS and compare them with onboard wind shear and altitude data collected during airplane approaches. Their results show good correlation between LCS extracted from the lidar data and updrafts and downdrafts experienced by landing aircraft. Overall, LCS analysis shows promise as a robust real-time tool to detect unsteady flow structures that impact airplane traffic.

Cluster observations of O+ escape in the magnetotail due to shock compression effects during the initial phase of the magnetic storm on 17 August 2001

We study the O+ outflow into the magnetotail during the initial phase of the 17 August 2001 magnetic storm. Solar wind and magnetospheric data are used from instruments onboard ACE, WIND, and Cluster spacecraft. The interplanetary shock arrival at Earth caused a large compression of the magnetosphere. During this event, the Cluster spacecraft were crossing the plasma sheet boundary layer of the magnetotail. Thus this case study constitutes a unique opportunity to observe the magnetotail response to a shock driven storm with multiple S/C data. We observed a field aligned oxygen (O+) outflow in the plasma sheet boundary layer and a bidirectional O+ flux in the central plasma sheet. Using the Cluster multiple spacecraft data, we derived the O+ gradient and the escape rate into the magnetotail during the initial phase of the magnetic storm. We found an escape rate of 4.0 × 1024 O+ ions s−1 in the plasma sheet boundary layer of the magnetotail, which is about 20 times the O+ inflow into the ring current during an intense magnetic storm.

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.

Spacecraft measurements of ions and electrons (>40 KeV) near and far upstream of the earth's bow shock

Two classes of proton enhancement can be recognised in the particle populations recorded upstream of the Earth's bow shock by the LION instrument onboard SOHO during a uniquely quiet period on the Sun in early 1996. These kinds of enhancement are, herein, defined to be events of Class 1 and Class 2 respectively. The flux profiles and characteristic features of Class 1 events suggest that they may be composed of particles accelerated at the bow shock. Class 2 events, which have different characteristics and co-relate with a high value of the geomagnetic index might, on the other hand, be associated with leakage from inside the magnetosphere, These possibilities of origin require further detailed study. On May 4, 1998 a population of particles accelerated up to ∼600 keV was identified in Interball and POLAR data at the Earth's (quasi-parallel) bow shock. Due to a lack of good magnetic connectivity, this population was not observed far upstream on SOHO (at L1) or onboard WIND. Records of relativistic electrons detected at SOHO and at Interball during a very active episode on the Sun in May 1998 are also presented and interpreted to have been associated with solar processes. These particles (unlike protons) were not dependent on the configuration of the interplanetary field to allow them to reach particular upstream locations. Such energetic electrons constitute a particular hazard to spacecraft.

Association of Low‐Charge‐State Heavy Ions up to 200 Re upstream of the Earth's bow shock with geomagnetic disturbances

We present the first study of Low‐Charge‐State Heavy Ion (LCSHI) events covering a region from Earth's bow shock to the L1 point, obtained with the Suprathermal Ion Composition Spectrometer onboard Wind. STICS is capable of distinguishing charge states of suprathermal ions. In 1995–2000 we found a large number of particle events revealing species of magnetospheric origin. LCSHI events tend to occur in series and in connection with geomagnetic activity. The occurrence rate is found to increase towards solar maximum. The spatial region covered by this particle population ranges from the bow shock to beyond distances of 130 Re, where one of the strongest events occurred. Based on the characterization of LCSHI events we discuss mechanisms for their formation. We conclude that the most probable sources of these ion events are substorms in association with Alfvén waves in high‐speed solar wind streams and the magnetic storm recovery ring current.

Influence of the solar-wind magnetic field on the magnetosheath turbulence behind the bow shock

The experiment Sura–-WIND (1996–1997) on radio-raying of geodisturbed solar-wind region is interpreted in terms of modern knowledge of an interaction between the magnetized solar wind and the Earth's magnetosphere. Characteristics of the scattered signal at 9 MHz, determined by a plasma turbulence level with scales about 100 km, are statistically related to in situ measurements of solar wind parameters such as plasma density and the orientation and magnitude of the interplanetary magnetic field (IMF) onboard WIND spacecraft. The dependence of the scintillation index of the detected scattered signal, characterising the average turbulence level of the Earth's magnetosheath behind the bow shock, on the IMF orientation and magnitude is revealed. To verify the relation obtained, modern nonlinear correlation techniques based on the theory of artificial neural networks (ANN) are applied. The results obtained using a three-layer ANN with error backpropagation confirm an essential IMF influence on the plasma turbulence in the magnetosheath.

Sura-wind radar: Studies of nonlinear effects using VHF-wave occultion of the ionosphere

We present experimental results on reception of VHF signals of the transmitting facility “Sura” of the Radiophysical Research Institute by the NASA spacecraft WIND. The experiments were performed during daytime during the summer seasons 1997–1998. The dependence of power and spectral characteristics of the VHF radio waves on the power of the sounding radiation is analyzed. We find that, in a wide range of effective powers of the VHF radiation from about 40 kW to 160 MW, the phenomena observed in the radiation received onboard WIND (such as focusing, scintillations, or frequency deviations of signals) does not usually depend on the operation mode of the “Sura” facility. At the same time, broadening of the radiation pattern of the facility and decrease of the mean level of the received signal by about 6 dB toward the direction of maximum of the radiation pattern were observed at the peak radiation power of the facility. The experimental results are compared to present concepts on effects of self-focusing instability and nonlinear defocusing of VHF radio waves in the ionospheric plasma.

Real-time onboard wind and windshear determination, part 2: Detection

Real-time onboard wind and windshear determination, part 2: Detection

Real-time onboard wind and windshear determination, part 1: Identification

Standard wind identification techniques employed in the analysis of aircraft accidents are post-facto techniques; they are processed after the event has taken place and are based on the complete time histories of the DFDR/ATCR data along the entire trajectory. By contrast, real-time wind identification techniques are processed while the event is taking place; they are based solely on the knowledge of the preceding time histories of the DFDR/ATCR data.

Reconstruction of flight path in turbulence

In the majority of previous investigations, compatibility checks of measured flight data have been carried out under the assumption of smooth air, neglecting atmospheric turbulence mainly because of its complexity of modeling. Based on the essential view of system theory, this paper proposes an effective strategy to reconstruct the flight path in turbulent air in two steps: 1) as in conventional methods, an error model for sensors, processors and a stationary windfield model are identified from flight maneuvers in smooth air; and 2) retaining some of the first step results pertaining to the inherent characteristics of data measurement and acquisition systems, a data consistency check for flight data in turbulent air is carried out using the same method as that in step 1 above. The two-step procedure eliminates the need for a turbulence model and, thus, yields identification results that are independent of wind model. Furthermore, use of this approach makes it possible to evaluate the precision of onboard wind measurement. The utility of the proposed approach is demonstrated by reconstructio n of longitudinal flight path from flight test in turbulence with the research aircraft DORNIER DO128.

Remote sensing of atmospheric winds using speckle–turbulence interaction, a CO_2 laser, and optical heterodyne detection

Speckle-turbulence interaction can be utilized to measure the vector wind in a plane perpendicular to the line of sight from a laser transmitter to a target. A continuous wave source of around 1 W and operating at 10.6 microm, in conjunction with an optical heterodyne receiver, has been used to measure atmospheric winds along horizontal paths. A theoretical basis, the experimental apparatus, processing techniques, and experimental results are presented. The technique has been demonstrated for remote sensing of atmospheric winds along horizontal paths but also has potential for global remote sensing of atmospheric winds and for onboard wind shear detection systems for aircraft. The results show that rms accuracies of the order of 0.5 m/s are possible with averaging times as short as 2 s.