Using unmanned aerial vehicle (UAV) photogrammetry for monitoring seasonal changes of barrier island in the southwestern coast of Taiwan

2020 ◽  
Author(s):  
Hui-Ju Hsu ◽  
Shyi-Jeng Chyi ◽  
Chia-Hung Jen ◽  
Lih-Der Ho ◽  
Jia-Hong Chen
Keyword(s):  
Summer Monsoon ◽  
Sand Dune ◽  
Vertical Direction ◽  
Barrier Island ◽  
Barrier Islands ◽  
Winter Monsoon ◽  
The Past ◽  
Monsoon Area ◽  
Area And Volume ◽  
Main Change

<p>The change of barrier islands could be a precursor of coastal landscape evolution. The barrier islands on the coast of southwest Taiwan are continuing narrowing and landward moving in the past decades. The government has tried to install eight detached embankments to protect Dingtoue barrier island in 2001. In this study, we try to monitor the landform change by using UAV photogrammetry. Dingtoue barrier island is 1.3 km in length and with area of 30.5 ha. We have already conducted 4 campaigns of UAV photogrammetry between March 2018 and September 2019, and they can reveal the landscape of the end of summer and winter monsoon. We use Agisoft Metashape to process the aerial photos for acquiring the DEM and ortho-rectified image with the spatial resolution of 0.5 m and precision level of 0.04 m in both horizontal and vertical direction. We sub-divide Dingtoue barrier island into beach and sand dune zones for further analysis by using Arc GIS. The DEM of difference and areas will be obtained in beach and sand dune as well.</p><p>The results show that area of Dingtoue barrier island is increasing 5101.2 sq.m, while volume of Dingtoue barrier island is decreasing 26722.1 cu.m at the end of the 2018 summer monsoon. The beach part is increasing in both area and volume, while the sand dune part is decreasing in both area and volume. The northern part of the beach is extending to east and the sand dune zone is retreating to further east. The southern part of the beach is extending to west part, which is the sea in the past. Area of Dingtoue barrier island is increasing 719.4 sq.m, while volume of Dingtoue barrier island is increasing 36705.7 cu.m at the end of the 2018 winter monsoon. Area of the beach part is relative the same as the previous period be with some minor changes in the northern and southern part. The sand dune part is increasing in both area and volume. Area of Dingtoue barrier island is increasing 14616.2 sq.m while volume of Dingtoue barrier island is decreasing 23894.1 cu.m at the end of the 2019 summer monsoon. Areas of beach and sand dune are both increasing while volume of the sand dune is decreasing. The mid-part of the beach is occupied by sand dune and the beach is recovering to previous shape.</p><p>In general, Dingtoue barrier island is increasing 7% in area and is decreasing 13910.5 cu.m in volume between March 2018 and September 2019. The average surface lowering is 0.05 m in this period. The trend shows that typhoons will increase area of Dingtoue barrier island, but decrease volume. The winter will decrease area of Dingtoue barrier island but increase volume. So the main change of area is at the beach part and the main change of volume is at the sand dune part. From the installation of the eight detached embankments can stabilize Dingtoue barrier island by increasing area, and volume is decreasing during the summer period and increasing in the winter period.</p>

scholarly journals A 5000-Year Sedimentary Record of East Asian Winter Monsoon from the Northern Muddy Area of the East China Sea

Atmosphere ◽  
2020 ◽  
Vol 11 (12) ◽  
pp. 1376
Author(s):  
Yanping Chen ◽  
Yan Li ◽  
Wenzhe Lyu ◽  
Dong Xu ◽  
Xibin Han ◽  
...  
Keyword(s):  
East China Sea ◽  
Summer Monsoon ◽  
Winter Monsoon ◽  
East China ◽  
Coarse Particles ◽  
The East China Sea ◽  
China Sea ◽  
The Past ◽  
Sedimentary Dynamics ◽  
Muddy Area

The variability of the winter monsoon is one of the key components of the Asian monsoon, significantly influencing paleoenvironmental evolution in East Asia. However, whether the winter or the summer monsoon is the dominated factor controlling sedimentary dynamics of the muddy areas of the continental shelves of the East China Sea is debated, due to lack of consistency between various winter monsoon proxies in previous studies. In this work, the sediments of the upper part of core ECS-DZ1 with several marine surface samples were studied in terms of sediment grain size and radiocarbon dating, and changes in sedimentary dynamics of the northern muddy area of the ECS over the past 5000 years were documented. The main findings are as follows: (1) regional sedimentary dynamics were low and did not significantly change since the middle Holocene; (2) coarse particles are the dominated component in the sediments; (3) a proxy can be derived to indicate changes in winter monsoon. Based on this reconstructed winter monsoon record, we found that this record was generally negatively correlated to the stalagmite-based summer monsoon variability over the past 3500 years, but positively correlated before that. Moreover, this record can be well correlated to changes in the Kuroshio Current and the Bond ice-rafting debris events in the North Atlantic on millennial timescales, inferring large-scale and common atmospheric dynamics across the Asian continent over the past 5000 years. Therefore, we concluded that the winter monsoon is the predominant factor controlling sedimentary dynamics in the northern part of the ECS and proposed that the contribution of coarse particles may be one of potential indices to identify the role of the winter and the summer monsoons in sedimentary evolution.

East Asian winter monsoon variation during the last 3000 years as recorded in a subtropical mountain lake, northeastern Taiwan

The Holocene ◽  
2021 ◽  
pp. 095968362110190
Author(s):  
Tsai-Wen Lin ◽  
Stefanie Kaboth-Bahr ◽  
Kweku Afrifa Yamoah ◽  
André Bahr ◽  
George Burr ◽  
...  
Keyword(s):  
Grain Size ◽  
East Asian Winter Monsoon ◽  
East Asian ◽  
Winter Monsoon ◽  
Mountain Lake ◽  
Sediment Grain Size ◽  
Global Monsoon ◽  
Asian Winter Monsoon ◽  
The Past ◽  
Monsoon System

The East Asian Winter Monsoon (EAWM) is a fundamental part of the global monsoon system that affects nearly one-quarter of the world’s population. Robust paleoclimate reconstructions in East Asia are complicated by multiple sources of precipitation. These sources, such as the EAWM and typhoons, need to be disentangled in order to understand the dominant source of precipitation influencing the past and current climate. Taiwan, situated within the subtropical East Asian monsoon system, provides a unique opportunity to study monsoon and typhoon variability through time. Here we combine sediment trap data with down-core records from Cueifong Lake in northeastern Taiwan to reconstruct monsoonal rainfall fluctuations over the past 3000 years. The monthly collected grain-size data indicate that a decrease in sediment grain size reflects the strength of the EAWM. End member modelling analysis (EMMA) on sediment core and trap data reveals two dominant grain-size end-members (EMs), with the coarse EM 2 representing a robust indicator of EAWM strength. The downcore variations of EM 2 show a gradual decrease over the past 3000 years indicating a gradual strengthening of the EAWM, in agreement with other published EAWM records. This enhanced late-Holocene EAWM can be linked to the expansion of sea-ice cover in the western Arctic Ocean caused by decreased summer insolation.

scholarly journals Feeding Experiments on Vittina Turrita (Mollusca, Gastropoda, Neritidae) Reveal Tooth Contact Areas and Bent Radular Shape During Foraging

2021 ◽  
Author(s):  
WENCKE KRINGS ◽  
CHRISTINE HEMPEL ◽  
LISA SIEMERS ◽  
MARCO NEIBER ◽  
STANISLAV GORB
Keyword(s):  
Experimental Approach ◽  
Tooth Wear ◽  
Ecological Niches ◽  
Control Group ◽  
Contact Areas ◽  
The Past ◽  
Feeding Experiments ◽  
Feeding Structure ◽  
3D Architecture ◽  
Area And Volume

Abstract The radula is the food gathering and processing structure and one important autapomorphy of the Mollusca. It is composed of a chitinous membrane with small, embedded teeth representing the interface between the organism and its ingesta. In the past, various approaches aimed at connecting the tooth shapes, which are highly distinct within single radulae due to their different functions. However, conclusions from the literature have been mainly drawn from microscopical analyses of mounted radulae, but the real interacting radular parts – even though the precise contact areas are essential for determining a tools functionality – and the 3D architecture of this complex feeding structure have not been previously determined. In the experimental approach presented here individuals of Vittina turrita (Neritidae, Gastropoda) were fed with algae paste attached to different sandpaper types. By comparison with radulae from a control group, sandpaper-induced tooth wear patterns were identified and both the area and volume loss were quantified. In addition to the exact contact area of each tooth, conclusions about the 3D position of teeth and the radular bending during feeding motion could be drawn. Furthermore, hypotheses about the specific functions of individual tooth types could be put forward. This kind of feeding experiments under controlled conditions is new for Mollusca and may provide a good basis for future studies on the radula functional morphology. It can be potentially applied to species with distinct tooth morphologies and ecological niches.

scholarly journals Three exceptionally strong East-Asian summer monsoon events during glacial conditions in the past 470 kyr

2008 ◽  
Vol 4 (6) ◽  
pp. 1289-1317 ◽  
Author(s):  
D.-D. Rousseau ◽  
N. Wu ◽  
Y. Pei ◽  
F. Li
Keyword(s):  
Summer Monsoon ◽  
Asian Monsoon ◽  
East Asian Monsoon ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Precipitation Regime ◽  
The Past ◽  
Ecological Requirements ◽  
Asian Summer ◽  
The Tropics

Abstract. Chinese loess sequences are interpreted as a reliable record of the past variation of the East Asian monsoon regime through the alternation of loess and paleosols units, dominated by the winter and summer monsoon, respectively. Different proxies have been used to describe this system, mostly geophysical, geochemical or sedimentological. Terrestrial mollusks are also a reliable proxy of past environmental conditions and are often preserved in large numbers in loess deposits. The analysis of the mollusk remains in the Luochuan sequence, comprising L5 loess to S0 soil, i.e. the last 500 ka, shows that for almost all identified species, the abundance is higher at the base of the interval (L5 to L4) than in the younger deposits. Using the present ecological requirements of the identified mollusk species in the Luochuan sequence allows the definition of two main mollusk groups varying during the last 500 kyr. The cold-aridiphilous individuals indicate the so-called Asian winter monsoon regime and predominantly occur during glacials, when dust is deposited. The thermal-humidiphilous mollusks are prevalent during interglacial or interstadial conditions of the Asian summer monsoon, when soil formation takes place. In the sequence, three events with exceptionally high abundance of the Asian summer monsoon indicators are recorded during the L5, L4 and L2 glacial intervals, i.e., at about 470, 360 and 170 kyr, respectively. The L5 and L4 events appear to be the strongest (high counts). Similar variations have also been identified in the Xifeng sequence, distant enough from Luochuan, but also in Lake Baikal further North, to suggest that this phenomenon is regional rather than local. The indicators of the summer monsoon within the glacial intervals imply a strengthened East-Asian monsoon interpreted as corresponding to marine isotope stages 6, 10 and 12, respectively. The L5 and L2 summer monsoons are coeval with Mediterranean sapropels S12 and S6, which characterize a strong African summer monsoon with relatively low surface water salinity in the Indian Ocean. Changes in the precipitation regime could correspond to a response to a particular astronomical configuration (low obliquity, low precession, summer solstice at perihelion) leading to an increased summer insolation gradient between the tropics and the high latitudes and resulting in enhanced atmospheric water transport from the tropics to the African and Asian continents. However, other climate drivers such as reorganization of marine and atmospheric circulations, tectonic, and the extent of the Northern Hemisphere ice sheet are also discussed.

scholarly journals Asian monsoon projection with a new large-scale monsoon definition

2021 ◽  
Author(s):  
Xingang Dai ◽  
Yang Yang ◽  
Ping Wang
Keyword(s):  
South Asia ◽  
Summer Monsoon ◽  
Moisture Transport ◽  
Large Scale ◽  
Asian Monsoon ◽  
Monsoon Season ◽  
Northwest China ◽  
Winter Monsoon ◽  
Climate Simulation ◽  
Northwestern Part

Abstract This paper focuses on Asian monsoon projection with CMIP5 multi-model outputs. A large-scale monsoon herewith is defined as a vector field of vertically integrated moisture flux from the surface to 500 hPa. Results demonstrate that the model ensemble mean underestimated the summer monsoon and overestimated slightly the winter monsoon over South Asia in both CMIP5 historical climate simulation and the monsoon projection for 2006–2015. The major of the bias is the model climate drift (MCD), which is removed in the monsoon projection for 2016–2045 under scenarios RCP4.5 for reducing the uncertainty. The projection shows that two increased moisture flows northward appeared across the Equator of Indian Ocean, the first is nearby Somalia coast toward northwestern part of South Asia, leading to excess rainfall in where the wet jet could reach, and the second starts from the equatorial Sect. (80°E–100°E) toward northeastern Bay of Bengal, leading to more rainfall spreading over the northwestern coast of Indochina Peninsula. In addition, a westward monsoon flow is intensified over the Peninsula leading to local climate moisture transport belt shifted onto South China Sea, which would reduce moisture transport toward Southwest China on one hand, and transport more moisture onto the southeast coast of the China mainland. The anomalous monsoon would result in a dry climate in Northwest China and wet climate in the coast belt during summer monsoon season for the period. Besides, the Asian winter monsoon would be seemingly intensified slightly over South Asia, which would bring a dry winter climate to Indian subcontinent, Northwest China, but would be more rainfall in southeast part of Arabian Peninsula with global climate warming.

scholarly journals The East Asian winter monsoon variability in response to precession and inter-hemispheric heat balance

2013 ◽  
Vol 9 (4) ◽  
pp. 4229-4261
Author(s):  
M. Yamamoto ◽  
H. Sai ◽  
M.-T. Chen ◽  
M. Zhao
Keyword(s):  
Northern Hemisphere ◽  
Summer Monsoon ◽  
Heat Balance ◽  
East Asian Winter Monsoon ◽  
East Asian ◽  
Winter Monsoon ◽  
Asian Winter Monsoon ◽  
Ice Volume ◽  
Monsoon Variability ◽  
Winter Insolation

Abstract. The response of Asian monsoon variability to orbital forcing is still unclear, and all hypotheses are controversial. We present a record of the sea surface temperature difference (ΔSST) between the South China Sea and the other Western Pacific Warm Pool regions as a proxy for the intensity of the Asian winter monsoon, because the winter cooling of the South China Sea is caused by the cooling of surface water at the northern margin and the southward advection of cooled water due to winter monsoon winds. The ΔSST showed significant precession cycles during the last 150 kyr. In the precession cycle, the maximum winter monsoon intensity shown by the ΔSST corresponded to the May perihelion and was delayed behind the maximum ice volume. The East Asian winter monsoon was anti-phase with the Indian summer monsoon and the summer monsoon precipitation in central Japan. The timing of the maximum phase of the East Asian winter monsoon was different from previous results in terms of the March perihelion (ice volume maxima) and June perihelion (minimum of Northern Hemisphere winter insolation). We infer that the variation of the East Asian winter monsoon was caused by a physical mechanism of inter-hemispheric heat balance. The East Asian winter monsoon was intensified by the Northern Hemisphere cooling, which was caused by the combined effect of cooling by the ice volume forcing and the decrease in winter insolation, or by decreased heat transfer from the Southern Hemisphere to the Northern Hemisphere owing to the weak Indian summer monsoon at the May perihelion.

Annual Cycle of Southeast Asia—Maritime Continent Rainfall and the Asymmetric Monsoon Transition

2005 ◽  
Vol 18 (2) ◽  
pp. 287-301 ◽  
Author(s):  
C-P. Chang ◽  
Zhuo Wang ◽  
John McBride ◽  
Ching-Hwang Liu
Keyword(s):  
Southeast Asia ◽  
Summer Monsoon ◽  
Annual Cycle ◽  
Asian Summer Monsoon ◽  
Small Region ◽  
Winter Monsoon ◽  
Boreal Summer ◽  
Boreal Winter ◽  
Maritime Continent ◽  
Asian Summer

Abstract In general, the Bay of Bengal, Indochina Peninsula, and Philippines are in the Asian summer monsoon regime while the Maritime Continent experiences a wet monsoon during boreal winter and a dry season during boreal summer. However, the complex distribution of land, sea, and terrain results in significant local variations of the annual cycle. This work uses historical station rainfall data to classify the annual cycles of rainfall over land areas, the TRMM rainfall measurements to identify the monsoon regimes of the four seasons in all of Southeast Asia, and the QuikSCAT winds to study the causes of the variations. The annual cycle is dominated largely by interactions between the complex terrain and a simple annual reversal of the surface monsoonal winds throughout all monsoon regions from the Indian Ocean to the South China Sea and the equatorial western Pacific. The semiannual cycle is comparable in magnitude to the annual cycle over parts of the equatorial landmasses, but only a very small region reflects the twice-yearly crossing of the sun. Most of the semiannual cycle appears to be due to the influence of both the summer and the winter monsoon in the western part of the Maritime Continent where the annual cycle maximum occurs in fall. Analysis of the TRMM data reveals a structure whereby the boreal summer and winter monsoon rainfall regimes intertwine across the equator and both are strongly affected by the wind–terrain interaction. In particular, the boreal winter regime extends far northward along the eastern flanks of the major island groups and landmasses. A hypothesis is presented to explain the asymmetric seasonal march in which the maximum convection follows a gradual southeastward progression path from the Asian summer monsoon to the Asian winter monsoon but experiences a sudden transition in the reverse. The hypothesis is based on the redistribution of mass between land and ocean areas during spring and fall that results from different land–ocean thermal memories. This mass redistribution between the two transition seasons produces sea level patterns leading to asymmetric wind–terrain interactions throughout the region, and a low-level divergence asymmetry in the region that promotes the southward march of maximum convection during boreal fall but opposes the northward march during boreal spring.

Decadal- to Centennial-Scale East Asian Summer Monsoon Variability Over the Past Millennium: An Oceanic Perspective

2018 ◽  
Vol 45 (15) ◽  
pp. 7711-7718 ◽  
Author(s):  
Richard Ching Wa Cheung ◽  
Moriaki Yasuhara ◽  
Briony Mamo ◽  
Kota Katsuki ◽  
Koji Seto ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
East Asian Summer Monsoon ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
The Past ◽  
Monsoon Variability ◽  
Asian Summer ◽  
Past Millennium
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