Yuping Guan

Combined effects of the Pacific Decadal Oscillation and El Niño-Southern Oscillation on Global Land Dry–Wet Changes

The effects of natural variability, especially El Niño-Southern Oscillation (ENSO) effects, have been the focus of several recent studies on the change of drought patterns with climate change. The interannual relationship between ENSO and the global climate is not stationary and can be modulated by the Pacific Decadal Oscillation (PDO). However, the global land distribution of the dry–wet changes associated with the combination of ENSO and the PDO remains unclear. In the present study, this is investigated using a revised Palmer Drought Severity Index dataset (sc_PDSI_pm). We find that the effect of ENSO on dry–wet changes varies with the PDO phase. When in phase with the PDO, ENSO-induced dry–wet changes are magnified with respect to the canonical pattern. When out of phase, these dry–wet variations weaken or even disappear. This remarkable contrast in ENSOs influence between the two phases of the PDO highlights exciting new avenues for obtaining improved global climate predictions. In recent decades, the PDO has turned negative with more La Niña events, implying more rain and flooding over land. La Niña-induced wet areas become wetter and the dry areas become drier and smaller due to the effects of the cold PDO phase.

Three‐dimensional oceanic eddy analysis in the Southern California Bight from a numerical product

With eight islands, complex coastlines and bottom topography, strong wind curls, and frequent upwelling fronts, the Southern California Bight (SCB) is an area with strong eddy activity. By applying an automated eddy detection scheme to a 12 year high-resolution numerical product of the oceanic circulation in the SCB, a three-dimensional eddy data set is developed. It includes information for each eddys location, polarity, intensity, size, boundary, and moving path at nine vertical levels. Through a series of statistical analyses applied to the eddy data set, three-dimensional statistical characteristics of mesoscale and submeoscale eddy variations in the SCB are elucidated; these shed light on how eddies are generated, evolve, and terminate. A significant percentage of eddies is found to be generated around islands and headlands along the coastline, which indicates that islands in the SCB play a vital role in eddy generation. Three types of eddies, based on shape, are identified from the numerical product: bowl, lens, and cone. A dynamic analysis shows that some submesoscale eddies with finite local Rossby numbers tend to be ageostrophic balanced while mesoscale eddies are in geostrophic balance. The present research results are useful for the interpretation of data sets obtained during the interdisciplinary Santa Barbara Channel Radiance in a Dynamic Ocean (RaDyo) field experiment conducted on September 3-25, 2008.

Fundamentals of a Magnetically Stabilized Fluidized Bed for Coal Separation

The performance of a magnetically stabilized fluidized bed is strongly affected by the properties of the air-fluidized dense medium, especially for the dry fine coal separation. The successful design and operation of a magnetically stabilized fluidized bed system for dry coal separation depend on the ability to accurately predict the fundamental properties of the fluidized bed, particularly the fluidized beds rheological properties and density. These properties are controlled and modified by magnetic field intensity and medium composition. The composition variables include medium density, magnetite particle size distribution, particle shape, and level of contamination. Some of these fundamentals of a magnetically stabilized fluidized bed for dry coal separation are described in this paper.

A Scheme to Identify Loops from Trajectories of Oceanic Surface Drifters: An Application in the Kuroshio Extension Region

When a drifter is trapped in an eddy, it makes either a cycloidal or a looping trajectory. The former case takes place when the translating speed is larger than the eddy spinning speed. When the background mean velocity is removed, drifter trajectories make loops. Thus, eddies can be detected from a drifter trajectory by identifying looping segments. In this paper, an automated scheme is developed to identify looping segments from Lagrangian trajectories,based on a geometric definition of a loop, that is, a closingcurve with its starting point overlapped by its ending point. The scheme is to find the first returning point, if it exists, along a trajectory of a surface drifter with a few other criteria. To further increase the chance that detected loops are eddies, it is considered that a loop identifies an eddy only when the loop’s spinning period is longer than the local inertial period and shorter than the seasonal scale, and that at least two consecutive loops with the same polarity that stay sufficiently close are found. Five parameters that characterize an eddy are estimated by the scheme: location (eddy center), time (starting and ending time), period, polarity, and intensity. As an example, the scheme is applied to surface drifters in the Kuroshio Extension region. Results indicate that numbers of eddies are symmetrically distributed for cyclonic and anticyclonic eddies, mean eddy sizes are 40‐ 50 km, and eddy abundance is the highest along the Kuroshio path with more cyclonic eddies along its southern flank.

Does the Asian monsoon modulate tropical cyclone activity over the South China Sea

To investigate whether the Asian monsoon influences tropical cyclone (TC) activity over the South China Sea (SCS), TCs (including tropical storms and typhoons) over the SCS are analyzed using the Joint Typhoon Warning Center dataset from 1945 to 2009. Results show an increasing trend in the frequencies of TC-all (all TCs over the SCS) and TY-all (all typhoons over the SCS), due mainly to an increase in the number of TCs moving into the SCS after development elsewhere. Little change is seen in the number of TCs that form in the SCS. The results of wavelet analysis indicate that the frequency of typhoons (TY) shows a similar oscillation as that of TCs, i.e., a dominant periodicity of 8–16 years around the 1970s for all TC activity, except for TC-mov (TCs that moved into the SCS from the western North Pacific). To examine the relationship between typhoon activity and the summer monsoon, a correlation analysis was performed that considered typhoons, TCs, and five monsoon indexes. The analysis reveals statistically significant negative correlation between the strength of the Southwest Asian summer monsoon and typhoon activity over the SCS, which likely reflects the effect of the monsoon on TC formation in the western North Pacific (WNP) and subsequent movement into the SCS. There is a statistically significant negative correlation between TY-loc (typhoons that developed from TCs formed over the SCS) and the South China Sea summer monsoon and Southeast Asian summer monsoon.

Numerical simulation and experimental validation of magnetic medium performance in air-dense medium fluidized bed (ADMFB)

The dynamic behavior of magnetic medium has a significant effect on the density of air-dense medium fluidized bed (ADMFB), and the density is an important parameter of ADMFB. This article introduces the model of ADMFB using multifluid hydrodynamic theories. The flow pattern of dense medium and the vertical density distribution in the ADMFB is obtained at the gas speed of 0.157 m/s. All the computed results are in a good agreement with experimental data. The results show that the flow pattern of dense medium ascends near the center and descends near the wall, and the density is stable along the vertical in the ADMFB.

Impacts of Four Types of ENSO Events on Tropical Cyclones Making Landfall over Mainland China Based on Three Best-track Datasets

Impacts of El Niño Modoki (ENM), La Niña Modoki (LNM), canonical El Niño (CEN) and canonical La Niña (CLN) on tropical cyclones (TCs) that made landfall over mainland China during 1951–2011 are analysed using best-track data from China, the USA and Japan. Relative to cold phase years (LNM and CLN), landfalling TCs in warm years (ENM and CEN) have a farther east genesis location, as well as longer track lengths and durations, both in total and before landfall. ENM demonstrates the highest landfall frequency, most northerly mean landfall position, and shortest after-landfall sustainability (track length and duration), which indicate a more frequent and extensive coverage of mainland China by TCs, but with shorter after-landfall influence. CEN has low landfall frequency and the most southerly mean landfall location. LNM has the most westerly genesis location, being significantly farther west than the 1951–2011 average and leading to short mean track lengths and durations both in total or before landfall, all of which are significantly shorter than the 1951–2011 average. Variations in the low-level wind anomaly, vertical wind shear, mid-level relative humidity, steering flow, the monsoon trough and the western Pacific subtropical high (WPSH) can to some extent account for the features of frequency, location, track length and duration of landfalling TCs. Since ENSO Modoki is expected to become more frequent in the near future, the results for ENSO Modoki presented in this paper are of particular significance.

Oscillation in frequency of tropical cyclones passing Taiwan and Hainan Islands and the relationship with summer monsoon

The temporal variations in the frequency of tropical cyclones (TCs) traversing the Taiwan and Hainan Islands (TH islands), were analyzed using a best-track TC dataset from the Joint Typhoon Warning Center for the period 1945–2007. Results show that the oscillations were interannual and interdecadal on the timescales of 2–8 and 8–12 years, respectively. It is also shown that the number of TCs formed in the western North Pacific basin (WNP) and of those traversing the TH islands varied intraseasonally. These results also held for typhoons traversing the TH islands, although the oscillations were less apparent. This study identified interrelationships between the frequency of TCs making landfall on the TH islands and the East Asia summer monsoon (EASM), the South Asia summer monsoon (SASM), and the South China Sea summer monsoon (SCSSM). The SCSSM significantly influenced the number of TCs traversing Hainan Island, but had little influence on the number of TCs traversing Taiwan Island. By contrast, the SASM influenced the numbers of TCs traversing both of the TH islands, shown by correlation coefficients of 0.41 for Taiwan Island and −0.25 for Hainan Island. In addition, the frequency of TC landfall on Taiwan Island increased during years of enhanced EASM, as indicated by a correlation coefficient of 0.4.

Effects of spectral nudging on the 2010 East Asia summer monsoon using WRF model

The performance of spectral nudging in an investigation of the 2010 East Asia summer monsoon was assessed using the Weather Research and Forecasting (WRF) model, forced by 1-degree NCEP Global Final Analysis (FNL). Two pairs of experiments were made, spectral nudging (SP) and non-spectral nudging (NOSP), with five members in each group. The members were distinguished by different initial times, and the analysis was based on the ensemble mean of the two simulation pairs. The SP was able to constrain error growth in large-scale circulation in upper-level, during simulation, and generate realistic regional scale patterns. The main focus was the model ability to simulate precipitation. The Tropical Rainfall Measuring Mission (TRMM) 3B42 product was used for precipitation verification. Mean precipitation magnitude was generally overestimated by WRF. Nevertheless, SP simulations suppressed overestimation relative to the NOSP experiments. Compared to TRMM, SP also improved model simulation of precipitation in spatial and temporal distributions, with the ability to reproduce movement of rainbands. However, extreme precipitation events were suppressed in the SP simulations.

Interbasin exchanges and their roles in global ocean circulation：A study based on 1 400 years＇ spin up of MOM4p1

A global prognostic model based on MOM4p1, which is a primitive equation nonBoussinesq numerical model, has been integrated with 1 400 years from the state of rest based on the realistic topography to study the long-term pattern of combined wind-driven and thermodynamically-driven general circulation. The model is driven by monthly climatological mean forces and includes 192×189 horizontal grids and 31 pressure-based vertical levels. The main objective is to investigate the mass and heat transports at inter-basin passages and their compensations and roles in the global ocean circulation under equilibrium state of long-term spin up. The kinetic energy analysis divides the spin up process into three stages: the quasi-stable state of wind driven current, the growing phase of thermodynamical circulation and the equilibrium state of thermohaline circulation. It is essential to spin up over a thousand years in order to reach the thermohaline equilibrium state from a state of rest. The Arctic Throughflow from the Bering Strait to the Greenland Sea and the Indonesian Throughflow (ITF) are captured and examined with their compensations and existing data. Analysis reveals that the slope structures of sea surface height are the dynamical driving mechanism of the Pacific-Arctic-Atlantic throughflow and ITF. The analysis denotes, in spite of O (1.4×106 m3/s) of the southward volume transport in the northern Atlantic, that there is still O (1 PW) of heat transported northward since the northward currents in the upper layer carrymuch higher temperature water than the southward flowing northern Atlantic deep water (NADW). Meridional volume and heat transports are focused on the contributions to NADW renewals and Atlantic meridional overturning circulation (AMOC). Quantitative descriptions of the interbasin exchanges are explained by meridional compensations and supported by previous observations and numerical modeling results. Analysis indicates that the volume and heat exchanges on the interbasin passages proposed in this article manifest their hub roles in the Great Ocean Conveyor System.