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  1. Free, publicly-accessible full text available February 1, 2024
  2. Key Points The external radiative forcing is the primary driver of the 1979–2013 warming for April–September, with varying decadal warming rates The interdecadal Pacific and Atlantic multidecadal variability intensify/dampen the warming when transitioning to positive/negative phase The combined effects of these factors reproduce the observed varied pace of decadal Arctic troposphere warming during 1979–2013
    Free, publicly-accessible full text available December 16, 2023
  3. Human experience involvement in existing operations of airborne Light Detection and Ranging (LIDAR) systems and off-line processing of collected LIDAR data make the acquisition process of airborne LIDAR point cloud less adaptable to environment conditions. This work develops a deep reinforcement learning-enabled framework for adaptive airborne LIDAR point cloud acquisition. Namely, the optimization of the airborne LIDAR operation is modeled as a Markov decision process (MDP). A set of LIDAR point cloud processing methods are proposed to derive the state space, action space, and reward function of the MDP model. A DRL algorithm, Deep Q-Network (DQN), is used to solve the MDP. The DRL model is trained in a flexible virtual environment by using simulator AirSim. Extensive simulation demonstrates the efficiency of the proposed framework.
  4. Abstract. The main drivers of the continental Northern Hemisphere snow cover are investigated in the 1979–2014 period. Four observational datasets are usedas are two large multi-model ensembles of atmosphere-only simulations with prescribed sea surface temperature (SST) and sea ice concentration (SIC). Afirst ensemble uses observed interannually varying SST and SIC conditions for 1979–2014, while a second ensemble is identical except for SIC witha repeated climatological cycle used. SST and external forcing typically explain 10 % to 25 % of the snow cover variance in modelsimulations, with a dominant forcing from the tropical and North Pacific SST during this period. In terms of the climate influence of the snow coveranomalies, both observations and models show no robust links between the November and April snow cover variability and the atmospheric circulation1 month later. On the other hand, the first mode of Eurasian snow cover variability in January, with more extended snow over western Eurasia, isfound to precede an atmospheric circulation pattern by 1 month, similar to a negative Arctic oscillation (AO). A decomposition of the variabilityin the model simulations shows that this relationship is mainly due to internal climate variability. Detailed outputs from one of the modelsindicate that the western Eurasia snow cover anomalies are precededmore »by a negative AO phase accompanied by a Ural blocking pattern and astratospheric polar vortex weakening. The link between the AO and the snow cover variability is strongly related to the concomitant role of thestratospheric polar vortex, with the Eurasian snow cover acting as a positive feedback for the AO variability in winter. No robust influence of theSIC variability is found, as the sea ice loss in these simulations only drives an insignificant fraction of the snow cover anomalies, with fewagreements among models.« less
    Free, publicly-accessible full text available January 1, 2024
  5. Tribble, C (Ed.)
    Abstract The majority of sequenced genomes in the monocots are from species belonging to Poaceae, which include many commercially important crops. Here, we expand the number of sequenced genomes from the monocots to include the genomes of 4 related cyperids: Carex cristatella and Carex scoparia from Cyperaceae and Juncus effusus and Juncus inflexus from Juncaceae. The high-quality, chromosome-scale genome sequences from these 4 cyperids were assembled by combining whole-genome shotgun sequencing of Nanopore long reads, Illumina short reads, and Hi-C sequencing data. Some members of the Cyperaceae and Juncaceae are known to possess holocentric chromosomes. We examined the repeat landscapes in our sequenced genomes to search for potential repeats associated with centromeres. Several large satellite repeat families, comprising 3.2–9.5% of our sequenced genomes, showed dispersed distribution of large satellite repeat clusters across all Carex chromosomes, with few instances of these repeats clustering in the same chromosomal regions. In contrast, most large Juncus satellite repeats were clustered in a single location on each chromosome, with sporadic instances of large satellite repeats throughout the Juncus genomes. Recognizable transposable elements account for about 20% of each of the 4 genome assemblies, with the Carex genomes containing more DNA transposons than retrotransposons while themore »converse is true for the Juncus genomes. These genome sequences and annotations will facilitate better comparative analysis within monocots.« less
  6. Abstract Large ensemble simulations with six atmospheric general circulation models involved are utilized to verify the interdecadal Pacific oscillation (IPO) impacts on the trend of Eurasian winter surface air temperatures (SAT) during 1998–2013, a period characterized by the prominent Eurasia cooling (EC). In our simulations, IPO brings a cooling trend over west-central Eurasia in 1998–2013, about a quarter of the observed EC in that area. The cooling is associated with the phase transition of the IPO to a strong negative. However, the standard deviation of the area-averaged SAT trends in the west EC region among ensembles, driven by internal variability intrinsic due to the atmosphere and land, is more than three times the isolated IPO impacts, which can shadow the modulation of the IPO on the west Eurasia winter climate.
  7. Abstract

    A detailed uplift history of the Tibetan Plateau is essential for disentangling the proposed geodynamical models and assessing its impacts on climate and biodiversity. However, when and how the plateau formed remains highly controversial. Here, we present unusual geochemical indicators of marine signatures in the Cenozoic terrestrial strata of the Qaidam Basin, northern Tibetan Plateau, with strong implications for the basin altitude. Our investigations across the basin reveal typical marine alkenones and anomalously high carbonate carbon isotopic values during the mid-Miocene, but not at earlier stages, which are accompanied by a divergent trend in the paired carbonate oxygen and leaf wax hydrogen isotopic records. We infer an incursion of seawater into the Qaidam Basin, thus constraining the mid-Miocene basin altitude close to sea level. Hence, much of the substantial northern plateau uplift afterwards appears to be associated with the outward growth of the Tibetan Plateau.