The interplay of wind and uplift facilitates over-water flight in facultative soaring birds

Flying over the open sea is energetically costly for terrestrial birds. Despite this, over-water journeys of many birds, sometimes hundreds of kilometres long, are uncovered by bio-logging technology. To understand how these birds afford their flights over the open sea, we investigated the role of atmospheric conditions, specifically wind and uplift, in subsidizing over-water flight at a global scale. We first established that Δ T , the temperature difference between sea surface and air, is a meaningful proxy for uplift over water. Using this proxy, we showed that the spatio-temporal patterns of sea-crossing in terrestrial migratory birds are associated with favourable uplift conditions. We then analysed route selection over the open sea for five facultative soaring species, representative of all major migratory flyways. The birds maximized wind support when selecting their sea-crossing routes and selected greater uplift when suitable wind support was available. They also preferred routes with low long-term uncertainty in wind conditions. Our findings suggest that, in addition to wind, uplift may play a key role in the energy seascape for bird migration that in turn determines strategies and associated costs for birds crossing ecological barriers such as the open sea.

Adaptive drift and barrier-avoidance by a fly-forage migrant along a climate-driven flyway

Background Route choice and travel performance of fly-forage migrants are partly driven by large-scale habitat availability, but it remains unclear to what extent wind support through large-scale wind regimes moulds their migratory behaviour. We aimed to determine to what extent a trans-equatorial fly-forage migrant engages in adaptive drift through distinct wind regimes and biomes across Africa. The Inter-tropical Front (ITF) marks a strong and seasonally shifting climatic boundary at the thermal equator, and we assessed whether migratory detours were associated with this climatic feature. Furthermore, we sought to disentangle the influence of wind and biome on daily, regional and seasonal travel performance. Methods We GPS-tracked 19 adult Eleonora’s falcons Falco eleonorae from the westernmost population on the Canary Islands across 39 autumn and 36 spring migrations to and from Madagascar. Tracks were annotated with wind data to assess the falcons’ orientation behaviour and the wind support they achieved in each season and distinct biomes. We further tested whether falcon routes across the Sahel were correlated with the ITF position, and how realized wind support and biome affect daily travel times, distances and speeds. Results Changes in orientation behaviour across Africa’s biomes were associated with changes in prevailing wind fields. Falcons realized higher wind support along their detours than was available along the shortest possible route by drifting through adverse autumn wind fields, but compromised wind support while detouring through supportive spring wind fields. Movements across the Sahel-Sudan zone were strongly associated to the ITF position in autumn, but were more individually variable in spring. Realized wind support was an important driver of daily travel speeds and distances, in conjunction with regional wind-independent variation in daily travel time budgets. Conclusions Although daily travel time budgets of falcons vary independently from wind, their daily travel performance is strongly affected by orientation-dependent wind support. Falcons thereby tend to drift to minimize or avoid headwinds through opposing wind fields and over ecological barriers, while compensating through weak or supportive wind fields and over hospitable biomes. The ITF may offer a climatic leading line to fly-forage migrants in terms of both flight and foraging conditions.

Far eastern curlew and whimbrel prefer flying low - wind support and good visibility appear only secondary factors in determining migratory flight altitude

Background In-flight conditions are hypothesized to influence the timing and success of long-distance migration. Wind assistance and thermal uplift are thought to reduce the energetic costs of flight, humidity, air pressure and temperature may affect the migrants’ water balance, and clouds may impede navigation. Recent advances in animal-borne long-distance tracking enable evaluating the importance of these factors in determining animals’ flight altitude. Methods Here we determine the effects of wind, humidity, temperature, cloud cover, and altitude (as proxy for climbing costs and air pressure) on flight altitude selection of two long-distance migratory shorebirds, far eastern curlew (Numenius madagascariensis) and whimbrel (Numenius phaeopus). To reveal the predominant drivers of flight altitude selection during migration we compared the atmospheric conditions at the altitude the birds were found flying with conditions elsewhere in the air column using conditional logistic mixed effect models. Results Our results demonstrate that despite occasional high-altitude migrations (up to 5550 m above ground level), our study species typically forego flying at high altitudes, limiting climbing costs and potentially alleviating water loss and facilitating navigation. While mainly preferring migrating at low altitude, notably in combination with low air temperature, the birds also preferred flying with wind support to likely reduce flight costs. They avoided clouds, perhaps to help navigation or to reduce the risks from adverse weather. Conclusions We conclude that the primary determinant of avian migrant’s flight altitude selection is a preference for low altitude, with wind support as an important secondary factor. Our approach and findings can assist in predicting climate change effects on migration and in mitigating bird strikes with air traffic, wind farms, power lines, and other human-made structures.

correlation between Low-level Jets and fog events in Tianjin

<p>Correlation between Low-level Jets and Fog Events in Tianjin  </p><p>Bingui Wu<sup>1,2</sup> Zongfei Li<sup>1,2</sup> , Tingting Ju<sup>3,&</sup>, Hongsheng Zhang<sup>4</sup></p><p><sup>1</sup> Affiliation:<sup></sup>Tianjin Key Labarotory of Marine Meteorology, Tianjin 300074, China.</p><p><sup>2</sup> Affiliation: Tianjin Meteorological Bureau, Tianjin 300074, China.</p><p>Address: Tianjin Meteorological Bureau, No.100 Weather Station Road Hexi District, Tianjin, 300074, China.</p><p><sup>3</sup> Affiliation: Institute of Navigation College, Dalian Maritime University, Dalian 116026, China</p><p>Address: Dalian Maritime University, No.1 LinghaiRoad Ganjingzi District, Dalian 116026, China<sup></sup></p><p><sup>4</sup> Affiliation: Laboratory for Climate and Ocean-Atmosphere Studies, Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing 100871, China</p><p>Address: Peking University, No.5 Yiheyuan Road Haidian District, Beijing 100871, China</p><p>KEY WORDS: low level jet, fog, Tianjin</p><p>Abstract</p><p>Fog and low level jet (LLJ) greatly affect aviation. Both of them are cared more, while not for their relationship. In this study, the relationship between the LLJs and fog are studied using the observational hourly wind profile data and the automatic meteorological observation data from Xiqing in 2016. The results show that LLJs play an important role in the fog events. The fog events tend to occur frequently with the occurrence of LLJs, especially in spring and summer, which suggest the LLJs seem to be more important for triggering advection fogs. In addition, the relationship between LLJs and fog events occur simultaneously and one, two and three days after the occurrence of LLJs are compared, and a pronounced relation are observed between LLJs and fog events one day after, a lag effect of LLJs on fog events is verified. For the condition that the LLJ and fog event occur on the same day, the differences of specific humidity between the occurrence of LLJs and fogs. In the case that the occurrence of LLJ is prior to fog, persistent southwest wind support the fog formation. While the differences of specific humidity between the occurrence of LLJs and fogs, in the case that the occurrence of LLJ is posterior to fog are always larger or close to zero, and the prevailing wind direction is north wind, which suggest that the main contribution of LLJs to fog is leading to fog dissipation and short duration in this condition. For the condition that the occurrence of LLJ one day prior to fog event, a pronounced negative correlation between the height of LLJs and the duration of fog is observed.</p>

Efektivitas Bukaan pada Rumah Bandayo Pobo’ide Terhadap Kenyamanan Fisiologis

Bandayo Pobo'ide is one of the traditional houses in Indonesia that uses natural ventilation as a physiological cooling. Nowadays, Bandayo Pobo'ide houses are used only for traditional ceremonies. In the past, the houses were used both for residence as well as for conducting traditional ceremonies. This affects the need for natural ventilation in the house. The role of openings is a major factor in providing physiological comfort in space. The percentage of openings that can accommodate the comfort of the room is 40% of the total wall area. This study aims to evaluate the effectiveness of openings for current activities. Field measurements were carried out to determine the phenomena in and around Bandayo Pobo'ide. Descriptive method was used to explain the effectiveness of the opening against the physiological comfort which will be calculated based on WSC (wind support comfort). The results showed that the openings were less than 40%, therefore the wind speed inside the building was relatively stagnant at 0.1m/s.

Decoupled Modelling Approaches for Environmental Interactions with Monopile-Based Offshore Wind Support Structures

To meet the political goals regarding renewable energy production, offshore wind keeps expanding to waters with larger depths and harsher conditions, while the turbine size continues to grow and ever-larger foundation structures are required. This development can only be successful if further cuts in the levelized cost of energy are established. Regarding the design of the foundation structures, a particular challenge in this respect relates to the reduction of the total computational time required for the design. For both practical and commercial reasons, the decoupled modelling of offshore wind support structures finds a common application, especially during the preliminary design stage. This modelling approach aims at capturing the relevant characteristics of the different environment-structure interactions, while reducing the complexity as much as possible. This paper presents a comprehensive review of the state-of-the-art modelling approaches of environmental interactions with offshore wind support structures. In this respect, the primary focus is on the monopile foundation, as this concept is expected to remain the prominent solution in the years to come. Current challenges in the field are identified, considering as well the engineering practice and the insights obtained from code comparison studies and experimental validations. It is concluded that the decoupled analysis provides valuable modelling perspectives, in particular for the preliminary design stage. In the further development of the different modelling strategies, however, the trade-off with computational costs should always be kept in mind.