Aviation Hazard Research Articles

Polarized view of supercooled liquid water clouds

Abstract Supercooled liquid water (SLW) clouds, where liquid droplets exist at temperatures below 0°C present a well-known aviation hazard through aircraft icing, in which SLW accretes on the airframe. SLW clouds are common over the Southern Ocean, and climate-induced changes in their occurrence is thought to constitute a strong cloud feedback on global climate. The two recent NASA field campaigns POlarimeter Definition EXperiment (PODEX, based in Palmdale, California, January–February 2013) and Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS, based in Houston, Texas in August–September 2013) provided a unique opportunity to observe SLW clouds from the high-altitude airborne platform of NASA's ER-2 aircraft. We present an analysis of measurements made by the Research Scanning Polarimeter (RSP) during these experiments accompanied by correlative retrievals from other sensors. The RSP measures both polarized and total reflectance in 9 spectral channels with wavelengths ranging from 410 to 2250 nm. It is a scanning sensor taking samples at 0.8° intervals within 60° from nadir in both forward and backward directions. This unique angular resolution allows for characterization of liquid water droplet size using the rainbow structure observed in the polarized reflectances in the scattering angle range between 135° and 165°. Simple parametric fitting algorithms applied to the polarized reflectance provide retrievals of the droplet effective radius and variance assuming a prescribed size distribution shape (gamma distribution). In addition to this, we use a non-parametric method, Rainbow Fourier Transform (RFT), which allows retrieval of the droplet size distribution without assuming a size distribution shape. We present an overview of the RSP campaign datasets available from the NASA GISS website, as well as two detailed examples of the retrievals. In these case studies we focus on cloud fields with spatial features varying between glaciated and liquid phases at altitudes as high as 10 km, which correspond to temperatures close to the homogeneous freezing temperature of pure water drops (about -35°C or colder). The multimodal droplet size distributions retrieved from RSP data in these cases are consistent with the multi-layer cloud structure observed by correlative Cloud Physics Lidar (CPL) measurements.

Roost site selection by ring‐billed and herring gulls

ABSTRACTGulls (Larus spp.) commonly roost in large numbers on inland and coastal waters, yet there is little information on how or where gulls choose sites for roosting. Roost site selection can lead to water quality degradation or aviation hazards when roosts are formed on water supply reservoirs or are close to airports. Harassment programs are frequently initiated to move or relocate roosting gulls but often have mixed results because gulls are reluctant to leave or keep returning. As such, knowledge of gull roost site selection and roosting ecology has applied and ecological importance. We used satellite telemetry and an information‐theoretic approach to model seasonal roost selection of ring‐billed (L. delawarensis) and herring gulls (L. argentatus) in Massachusetts, USA. Our results indicated that ring‐billed gulls preferred freshwater roosts and will use a variety of rivers, lakes, and reservoirs. Herring gulls regularly roosted on fresh water but used salt water roosts more often than ring‐billed gulls and also roosted on a variety of land habitats. Roost modeling showed that herring and ring‐billed gulls selected inland fresh water roosts based on size of the water body and proximity to their last daytime location; they selected the largest roost closest to where they ended the day. Management strategies to reduce or eliminate roosting gulls could identify and try to eliminate other habitat variables (e.g., close‐by foraging sites) that are attracting gulls before attempting to relocate or redistribute (e.g., through hazing programs) roosting birds. © 2016 The Wildlife Society.

Validation of ASH Optical Depth and Layer Height from IASI using Earlinet Lidar Data

The 2010 eruptions of the Icelandic volcano Eyjafjallajokull attracted the attention of the public and the scientific community to the vulnerability of the European airspace to volcanic eruptions. The European Space Agency project “Satellite Monitoring of Ash and Sulphur Dioxide for the mitigation of Aviation Hazards”, called for the creation of an optimal End-to-End System for Volcanic Ash Plume Monitoring and Prediction. This system is based on improved and dedicated satellite-derived ash plume and sulphur dioxide level assessments, as well as an extensive validation, using among others ground-based measurements (Koukouli et al., 2014). The validation of volcanic ash levels and height extracted from IASI/MetopA is presented in this work with emphasis on the ash plume height and ash optical depth levels. European Aerosol Research Lidar Network [EARLINET] lidar measurements are compared to different satellite estimates for two eruptive episodes. The validation results are extremely promising within the estimated uncertainties of each of the comparative datasets.

Aviation Hazards in the Sky over Thada as Revealed by Meso-scale Meteorological Modeling

The airplane of Nepal Army in-route to Kathmandu Airport from Nepalgunj lost its communication with the air traffic control room from the sky of Thada of Arghakhachi District. The plane was found with breath taking crashing over the Bowang high mountain area of Baglung District. The weather pattern over the area has been numerically reconstructed with the application of Weather Research and Forecasting (WRF) model initialized with NCEP FNL meteorological and USGS land use and terrain elevation data to examined the effect of prevailing weather pattern. The reconstructed weather pattern show that the atmosphere over Thada and associated areas capture an adverse condition for aviation activities, as it appears highly turbulent and is intense subsidence prone. A detail long-term investigation usefully complemented with field observation may provide better understanding and for improved flight safety.Journal of Institute of Science and Technology, 2014, 19(2): 65-70

Aviation Hazards Over the Jomsom Airport of Nepal as Revealed by Numerical Simulation of Local Flows

Jomsom Airport of Nepal is considered to be one of the world’s most extreme airports. The frequency of aircraft crashing along the Kali Gandaki River Valley and over the Jomsom Airport is very high. Pre-monsoon time local flow characteristics over the Kali Gandaki Valley has been studied to understand the meteorological hazards for aviation activities along the valley and over the Jomsom Airport with the application of the WRF Modeling System initialized with NCEP meteorological, USGS 24 categories land use, and 30 second terrain data. Four days long simulation was carried out for the period of 15 May 0000 UTC to 19 May 0000 UTC, 2012 to capture the 16 May 2012 incidence of light aircraft crashing in the late morning time of the day. The study revealed that there are enough grounds to believe that the crashing of the plane resulted due to the adverse local flow system prevailing over the Jomsom Airport area during the period. The significant subsidence from the relatively strong boundary layer wind aloft, the ground level opposite wind and the low-level turbulence might have leaded the airplane to crash just after its takeoff from the runway. The local flow system over the Kali Gandaki Valley makes afternoon time flights over the Jomsom Airport almost impossible and the narrow slot of time during morning time is also not free from difficult situation. Journal of Institute of Science and Technology, 2014, 19(1): 111-120

MATISSE: an ArcGIS tool for monitoring and nowcasting meteorological hazards

Abstract. Adverse meteorological conditions are one of the major causes of accidents in aviation, resulting in substantial human and economic losses. For this reason it is crucial to monitor and early forecast high impact weather events. In this context, CIRA (Italian Aerospace Research Center) has implemented MATISSE (Meteorological AviaTIon Supporting SystEm), an ArcGIS Desktop Plug-in able to detect and forecast meteorological aviation hazards over European airports, using different sources of meteorological data (synoptic information, satellite data, numerical weather prediction models data). MATISSE presents a graphical interface allowing the user to select and visualize such meteorological conditions over an area or an airport of interest. The system also implements different tools for nowcasting of meteorological hazards and for the statistical characterization of typical adverse weather conditions for the airport selected.

Influence of solidification on the impact of supercooled water drops onto cold surfaces

This study presents an experimental investigation of the impact of a supercooled drop onto hydrophilic and superhydrophobic substrates. The aim is to better understand the process of airframe icing caused by supercooled large droplets, which has been recently identified as a severe hazard in aviation. The Weber number and Reynolds number of the impinging drop ranged from 200 to 300 and from 2600 to 5800, respectively. Drop impact, spreading, and rebound were observed using a high-speed video system. The maximum spreading diameter of an impacting drop on hydrophilic surfaces was measured. The temperature effect on this parameter was only minor for a wide range of the drop and substrate temperatures. However, ice/water mixtures emerged when both the drop and substrate temperatures were below 0 °C. Similarly, drop rebound on superhydrophobic substrates was significantly hindered by solidification when supercooled drop impacted onto substrates below the freezing point. The minimum receding diameter and the speed of ice accretion on the substrate were measured for various wall temperatures. Both parameters increased almost linearly with decreasing wall temperature, but eventually leveled off beyond a certain substrate temperature. The rate of ice formation on the substrate was significantly higher than the growth rate of free ice dendrites, implying that multiple nucleation sites were present.

Atmospheric dependency of the sensitivity of infrared satellite observations to volcanic ash clouds

Volcanic ash can travel great distances and sometimes persist for several weeks, necessitating the monitoring of large areas for potential aviation hazards. Ash can affect aircraft in several ways, from engine failure to manageable impacts if the ash concentration is low. The location and properties of even low levels of ash are, therefore, required in order to make informed safety decisions. Infrared (IR) satellite-borne sensors are vital to this monitoring because of their high spatial coverage day and night. Interpretation of IR ash observations generally relies on exploiting the difference between an observation and the observation anticipated for the same scene under ash-free conditions, the so-called ash signal. We apply forward-model observations of andesitic ash with a fixed particle size distribution to investigate the sensitivity of ash signals to the ambient atmosphere. The variability in the ash signals attributable to atmospheric effects is found to be at least as high as the variability attributable to differences in ash concentration and altitude, implying that different concentrations could be retrieved if atmospheric effects were ignored. Ash with different optical properties is likely to correspond to a slightly different ash signal and may exhibit a different sensitivity to atmospheric effects to that presented here.

Impact evaluation of potential volcanic plumes over Spain

The volcanic ash transport to Spain has been investigated as a part of a broader scale forecast system. Based on a double criterion, distance and eruptive history, four volcanic areas potentially affecting Spain have been investigated: Azores Islands (Portugal), Canary Islands (Spain), Iceland, and southern Italy. The paths of simulated plumes have been computed from daily forward trajectories for the period 2005–2012 using the volcanoes' locations as departure points. The frequency of impact of the hypothetical plumes has been calculated for eight regions in Spain. The probability in all cases is low. Portuguese and Spanish volcanoes present the highest probability in the warm season (~3.5%); the volcanic ash from Iceland would be expected to arrive mainly in the cold season (<1.5%). Italian volcanoes show the lowest probability (<0.5%). The weather patterns associated to the arrival of volcanic plumes from the four volcanic areas have been identified. The mean times required for the ash plumes to reach Spain from the Canary Islands, Azores Islands, Iceland, and Italy are 40, 42, 57, and 61h, respectively. The HYSPLIT model has been used to study the volcanic plumes' dispersion and concentration fields in three aviation reference atmospheric layers. Values with high hazard for aviation have been obtained over Spain following the hypothetical eruption of a Canary Islands volcano. Fields of medium hazard would be found over Spain after a Portuguese volcano eruption. The volcanic ash from Icelandic volcanoes shows low hazard, while Italian volcanoes indicate a null hazard in most cases.

Intercomparison of Metop-A SO2 measure- ments during the 2010- 2011 Icelandic eruptions

&lt;p&gt;&lt;em&gt;The European Space Agency project &lt;/em&gt;Satellite Monitoring of Ash and Sulphur Dioxide for the mitigation of Aviation Hazards&lt;em&gt;, was introduced after the eruption of the Icelandic volcano Eyjafjallajökull in the spring of 2010 to facilitate the development of an optimal End-to-End System for Volcanic Ash Plume Monitoring and Prediction. The Eyjafjallajökull plume drifted towards Europe and caused major disruptions of European air traffic for several weeks affecting the everyday life of millions of people. The limitations in the volcanic plume monitoring and prediction capabilities gave birth to this observational system which is based on comprehensive satellite-derived ash plume and sulphur dioxide [SO&lt;sub&gt;2&lt;/sub&gt;] level estimates, as well as a widespread validation using supplementary satellite, aircraft and ground-based measurements. &lt;/em&gt;&lt;em&gt;The validation of volcanic total column SO&lt;sub&gt;2&lt;/sub&gt; measured by GOME-2/MetopA and IASI/MetopA are shown before, during and after the Eyjafjallajökull 2010 eruptions as well as for the 2011 Grimsvötn eruption. Co-located ground-based Brewer Spectrophotometer data extracted from the World Ozone and Ultraviolet Radiation Data Centre are also compared to the different satellite estimates&lt;/em&gt;&lt;/p&gt;

Extending the long‐term record of volcanic SO2 emissions with the Ozone Mapping and Profiler Suite nadir mapper

AbstractUninterrupted, global space‐based monitoring of volcanic sulfur dioxide (SO2) emissions is critical for climate modeling and aviation hazard mitigation. We report the first volcanic SO2 measurements using ultraviolet (UV) Ozone Mapping and Profiler Suite (OMPS) nadir mapper data. OMPS was launched on the Suomi National Polar‐orbiting Partnership satellite in October 2011. We demonstrate the sensitivity of OMPS SO2 measurements by quantifying SO2 emissions from the modest eruption of Paluweh volcano (Indonesia) in February 2013 and tracking the dispersion of the volcanic SO2 cloud. The OMPS SO2 retrievals are validated using Ozone Monitoring Instrument and Atmospheric Infrared Sounder measurements. The results confirm the ability of OMPS to extend the long‐term record of volcanic SO2 emissions based on UV satellite observations. We also show that the Paluweh volcanic SO2 reached the lower stratosphere, further demonstrating the impact of small tropical volcanic eruptions on stratospheric aerosol optical depth and climate.

Fusion characteristics of volcanic ash relevant to aviation hazards

The fusion dynamics of volcanic ash strongly impacts deposition in hot parts of jet engines. In this study, we investigate the sintering behavior of volcanic ash using natural ash of intermediate composition, erupted in 2012 at Santiaguito Volcano, Guatemala. A material science procedure was followed in which we monitored the geometrical evolution of cylindrical-shaped volcanic ash compact upon heating from 50 to 1400°C in a heating microscope. Combined morphological, mineralogical, and rheological analyses helped define the evolution of volcanic ash during fusion and sintering and constrain their sticking potential as well as their ability to flow at characteristic temperatures. For the ash investigated, 1240°C marks the onset of adhesion and flowability. The much higher fusibility of ash compared to that of typical test sands demonstrates for the need of a more extensive fusion characterization of volcanic ash in order to mitigate the risk posed on jet engine operation.

Intensity of thunderstorm-generated turbulence revealed by large-eddy simulation

Thunderstorms are characterized by turbulent processes that constitute an important aviation hazard and cause vertical transport of atmospheric constituents. Turbulence occurs within cloud and in the surrounding clear air, but, despite its importance, the characteristics of thunderstorm-generated turbulence and its spatial distribution are poorly understood, especially outside of cloud. Here we use large-eddy simulation to characterize turbulence generated by a canonical thunderstorm. The simulation identifies regions of notable three-dimensional anisotropic turbulence more than 5 km above the storm, in a shallow layer above the storm's anvil, and a horizontally asymmetric pattern of weaker turbulence that extends more than 50 km horizontally away from the cloud. Our results provide the first continuous estimate of turbulence intensity in and around thunderstorms and represent a major step toward improved turbulence avoidance methods. The results have broader implications for understanding the fundamental aspects of how thunderstorms affect their environment through vertical exchange processes.

Assessment and Characterization of Volcanic Ash Threat to Gas Turbine Engine Performance

Multiple volcanoes erupt yearly propelling volcanic ash into the atmosphere and creating an aviation hazard. The plinian eruption type is most likely to create a significant aviation hazard. Plinian eruptions can eject large quantities of fine ash up to an altitude of 50,000 m (164,000 ft). While large airborne particles rapidly fall, smaller particles at reduced concentrations drift for days to weeks as they gradually descend and deposit on the ground. Very small particles, less than 1 μm, can remain aloft for years. An average of three aircraft encounters with volcanic ash was reported every year between 1973 and 2003. Of these, eight resulted in some loss of engine power, including a complete shutdown of all four engines on a Boeing 747. However, no crashes have been attributed to volcanic ash. The major forms of engine damage caused by volcanic ash are: (1) deposition of ash on turbine nozzles and blades due to glassification (2) erosion of compressor and turbine blades (3) carbon deposits on fuel nozzles. The combination of these effects can push the engine to surge and flame out. If a flame out occurs, engine restart may be possible. Less serious engine damage can also occur. In most cases the major damage will require an engine overhaul long before the minor damage becomes an operational issue, but under some conditions no sign of volcanic ash is evident and the turbine cooling system blockage could go unnoticed until an engine inspection is performed. Several organizations provide aircrew procedures to respond to encounters with a volcanic ash cloud. If a volcanic ash encounter is suspected, then an engine inspection, including borescope, should be performed with particular attention given to the turbine cooling system.

Simulation of Airborne Radar Observations of Precipitating Systems at Various Frequency Bands

This paper addresses the question of the most efficient couple (f, θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3dB</sub> ) for airborne radar precipitating system observations, where f is the microwave frequency and θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3dB</sub> is the beamwidth aperture at 3 dB. This problem is of importance. The meteorological hazard in civil aviation is mainly due to convective precipitating systems, particularly hail and strong turbulence areas. A realistic and flexible model of precipitating systems is presented, and simulations of airborne radar observations are performed at the six meteorological frequency bands (S, C, X, K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> , K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sub> , and W). In this paper, the effect of f and θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3dB</sub> modification is shown through radar simulations of two precipitating systems. One is a numerical simulation composed of two successive rows of convective towers; the other is inspired from a real mesoscale system, presenting hail-bearing convective towers. It is shown that some (f, θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3dB</sub> ) couples are better than the one currently used by civil aviation. Notably, C band allows a better description than X band of a meteorological radar scene if the radar antenna size is increased. The model and methodology presented herein are adaptable to ground-based and satellite radars.

Ice Fog in Arctic During FRAM–Ice Fog Project: Aviation and Nowcasting Applications

Ice fog and frost occur commonly (at least 26% of the time) in the northern latitudes and Arctic regions during winter at temperatures usually less than about –15°C. Ice fog is strongly related to frost formation—a major aviation hazard in the northern latitudes. In fact, it may be considered a more dangerous event than snow because of the stronger aircraft surface adhesion compared to snow particles. In the winter of 2010/11, the Fog Remote Sensing and Modeling–Ice Fog (FRAM-IF) project was organized near Yellowknife International Airport, Northwest Territories, Canada, with the main goals of advancing understanding of ice fog microphysical and visibility characteristics, and improving its prediction using forecast models and remotesensing retrievals. Approximately 40 different sensors were used to measure visibility, precipitation, ice particle spectra, vertical thermodynamic profiles, and ceiling height. Fog coverage and visibility parameters were estimated using both Geostationary Operational Environmental Satellites (GOES) and Moderate Resolution Imaging Spectroradiometer (MODIS) satellite observations. During this project, the inversion layer usually was below a height of 1.5 km. High humidity typically was close to the ground, frequently producing ice fog, frost, and light snow precipitation. At low temperatures, snow crystals can be swept away by a very low wind speed (∼1 m s−1). Ice fog during the project was not predicted by any forecast model. These preliminary results in the northern latitudes suggest that ice fog and frost studies, over the Arctic regions, can help us to better understand ice microphysical processes such as ice nucleation, visibility, and parameterizations of ice fog.

Perspective: Thorniest Issues In Healthcare

<i>Perspective:</i> Thorniest Issues In Healthcare

SO2 as a possible proxy for volcanic ash in aviation hazard avoidance

Airborne volcanic ash poses a significant danger to aircraft, but is difficult to quantify accurately using satellite data, while sulphur dioxide is much easier to detect accurately, but is much less of a direct hazard to aviation. This paper investigates the reliability of using SO2 as a proxy for the location of volcanic ash, using an SO2 retrieval from the Infrared Atmospheric Sounding Interferometer (IASI) and ash detections from IASI and the Advanced Along Track Scanning Radiometer (AATSR). Using a numerical “missed ash fraction” applied to the eruptions of Eyjafjallajökull in 2010 and Puyehue‐Cordón Caulle in 2011 reveals that the SO2 flag typically misses ∼30% of the detectable ash. Furthermore, the missed ash fraction is found to be highly variable, both between the two eruptions and over the course of each eruption, with values of over 80% found on some days. The detection threshold of the AATSR ash flag is also investigated using radiative transfer calculations, allowing the threshold of the IASI flag to be inferred, and these are related to the ash contamination levels.

Study of atmospheric refractivity prior to squall onset and its strong association with surface temperature and relative humidity over Kolkata (22°34′N, 88°22′E)

The paper presents the nature of variation of refractive index of atmospheric medium before the onset of squall over kolkata (22°34′N 88°22′E), India. The variation of the refractive index with surface temperature and relative humidity during squall is also presented. It is concluded that sharp decrease of the refractivity may be taken as a possible method of forecasting squall. This kind of study is very much helpful from the standpoint of aviation hazards and communication. Possible explanation for the observed results is also presented.

Interaction between volcanic plumes and wind during the 2010 Eyjafjallajökull eruption, Iceland

Estimates of volcanic source mass flux, currently deduced from observations of plume height, are crucial for ash dispersion models for aviation and population hazard. This study addresses the role of the atmospheric wind in determining the height at which volcanic plumes spread in the atmosphere and the relationship between source mass flux and plume height in a wind field. We present a predictive model of volcanic plumes that describes the bending over of the plume trajectory in a crosswind and show that model predictions are in accord with a dataset of historic eruptions if the profile of atmospheric wind shear is described. The wind restricts the rise height of volcanic plumes such that obtaining equivalent rise heights for a plume in a windy environment would require an order of magnitude increase in the source mass flux over a plume in a quiescent environment. Our model calculations are used to calibrate a semi‐empirical relationship between the plume height and the source mass flux that explicitly includes the atmospheric wind speed. We demonstrate that the model can account for the variations in plume height observed during the first explosive phase of the 2010 Eyjafjallajökull eruption using independently measured wind speeds and show that changes in the observed plume height are better explained by changing meteorology than abrupt changes in the source mass flux. This study shows that unless the wind is properly accounted for, estimates of the source mass flux during an explosive eruption are likely to be very significant underpredictions of the volcanic source conditions.