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Kwon Y.C.,Prediction Institute | Hong S.-Y.,Prediction Institute
Monthly Weather Review | Year: 2017

A method that enables a mass-flux cumulus parameterization scheme (CPS) to work seamlessly in various model grids across CPS gray-zone resolutions is proposed. The convective cloud-base mass flux, convective inhibition, and convective detrainment in the simplified Arakawa-Schubert (SAS) scheme are modified to be functions of the convective updraft fraction. The combination of two updraft fractions is used to modulate the cloud-base mass flux; the first one depends on the horizontal grid space and the other is a function of the grid-scale and convective vertical velocity. The convective inhibition and detrainment of hydrometeors are also modified to be a function of the grid-size-dependent convective updraft fraction. A set of sensitivity experiments with the Weather Research and Forecasting (WRF) Model is conducted for a heavy rainfall case over South Korea. The results show that the revised SAS CPS outperforms the original SAS. At 3 and 1 km, the precipitation core over South Korea is well reproduced by the experiments with the revised SAS scheme. On the contrary, the simulated precipitation is widespread in the case of the original SAS experiment and there are multiple spurious cores when the CPS is removed at those resolutions. The modified mass flux at the cloud base is found to play a major role in organizing the grid-scale precipitation at the convective core. A 1-month simulation at 3 km confirms that the revised scheme produces slightly better summer monsoonal precipitation results as compared to the typical model setup without CPS. © 2017 American Meteorological Society.

Pisarenko V.F.,Prediction Institute | Sornette D.,ETH Zurich
European Physical Journal: Special Topics | Year: 2012

We ask the question whether it is possible to diagnose the existence of "Dragon-Kings" (DK), namely anomalous observations compared to a power law background distribution of event sizes. We present two new statistical tests, the U-test and the DK-test, aimed at identifying the existence of even a single anomalous event in the tail of the distribution of just a few tens of observations. The DK-test in particular is derived such that the p-value of its statistic is independent of the exponent characterizing the null hypothesis, which can use an exponential or power law distribution. We demonstrate how to apply these two tests on the distributions of cities and of agglomerations in a number of countries. We find the following evidence for Dragon-Kings: London in the distribution of city sizes of Great Britain; Moscow and St-Petersburg in the distribution of city sizes in the Russian Federation; and Paris in the distribution of agglomeration sizes in France. True negatives are also reported, for instance the absence of Dragon-Kings in the distribution of cities in Germany. © 2012 EDP Sciences and Springer.

Shin H.H.,U.S. National Center for Atmospheric Research | Hong S.-Y.,Prediction Institute
Monthly Weather Review | Year: 2015

Parameterization of the unresolved vertical transport in the planetary boundary layer (PBL) is one of the key physics algorithms in atmospheric models. This study attempts to represent the subgrid-scale (SGS) turbulent transport in convective boundary layers (CBLs) at gray-zone resolutions by investigating the effects of grid-size dependency in the vertical heat transport parameterization for CBL simulations. The SGS transport profile is parameterized based on the 2013 conceptual derivation by Shin and Hong. First, nonlocal transport via strong updrafts and local transport via the remaining small-scale eddies are separately calculated. Second, the SGS nonlocal transport is formulated by multiplying a grid-size dependency function with the total nonlocal transport profile fit to the large-eddy simulation (LES) output. Finally, the SGS local transport is formulated by multiplying a grid-size dependency function with the total local transport profile, which is calculated using an eddy-diffusivity formula. The new algorithm is evaluated against the LES output and compared with a conventional nonlocal PBL parameterization. For ideal CBL cases, by considering the scale dependency in the parameterized vertical heat transport, improvements over the conventional nonlocal K-profile model appear in mean profiles, resolved and SGS vertical transport profiles with their grid-size dependency, and the energy spectrum. Real-case simulations for convective rolls show that the simulated roll structures are more robust with stronger intensity when the new algorithm is used. © 2015 American Meteorological Society.

Flatau M.,U.S. Navy | Kim Y.-J.,U.S. Navy | Kim Y.-J.,Prediction Institute
Journal of Climate | Year: 2013

A tropical-polar connection and its seasonal dependence are examined using the real-time multivariate Madden-Julian oscillation (MJO) (RMM) index and daily indices for the annular modes, the Arctic Oscillation (AO) and the Antarctic Oscillation (AAO). On the intraseasonal time scale, the MJO appears to force the annular modes in both hemispheres. On this scale, during the cold season, the convection in the Indian Ocean precedes the increase of the AO/AAO. Interestingly, during the boreal winter (Southern Hemisphere warm season), strong MJOs in the Indian Ocean are related to a decrease ofthe AAO index, and AO/AAO tendencies are out of phase. On the longer time scales, a persistent AO/AAO anomaly appears to influence the convection in the tropical belt and impact the distribution of MJO-preferred phases. It is shown that this may be a result of the sea surface temperature (SST) changes related to a persistent AO, with cooling over the Indian Ocean and warming over Indonesia. In the Southern Hemisphere, the SST anomalies are to some extent also related to a persistent AAOpattern, but this relationship is much weaker and appears only during the Southern Hemisphere cold season. Onthe basis of these results, a mechanism involving the air-sea interaction in the tropics is suggested as a possible link between persistent AO and convective activity in the Indian Ocean and western Pacific.

The seismic process is usually treated as en example of development of self-organized criticality (SOC). However, implementation mechanisms of SOC in the case of a seismic process have not been proposed. In the present work, the seismicity is modeled as a sequence of a variety of stochastic episodes of avalanche-like relaxation of metastable subsystems. The model reproduces all known empirical features inherent in the seismic process. The simulated pattern of behavior was revealed to agree with the empirical regularities, which promotes an understanding of the physics of the seismic process. © 2011 Pleiades Publishing, Ltd.

A method of converting coordinates of a physical quantity from a latitude-longitude coordinates system to a rotated cubed-sphere coordinates system is disclosed. The method is performed in a hardware device including a computation part and a memory. A plurality of latitude-longitude grid areas which overlap a cubed-sphere grid area is determined. An overlapping area between the cubed-sphere grid area and the latitude-longitude grid areas is computed.

A method of visualizing numerical weather prediction model data on a six-panel grid frame is disclosed. Global map data are converted from latitude-longitude coordinates into coordinates in the six-panel grid frame. The six-panel grid frame are provided with numerical weather prediction model data in a first cubed-sphere coordinates system. The numerical weather prediction model data are displayed on the six-panel grid frame. The six-panel grid frame includes expanded six faces of a virtual cube. Each face of the expanded six faces is defined by four sub-faces of eight sub-cubes which are assembled with each other within the virtual cube.

A method of parallelizing computation in an element and communication between elements in a cubed-sphere coordinates system based on a spectral element method is disclosed. The method is performed in a hardware device including a computation part, a memory and a communication buffer. A first grid value at a first grid point in a first element among elements within group of a first group is computed according to a predetermined numerical equation substantially at the same time as a second grid value at a second grid point in a second element of the first group is sent to or received from the communication buffer.

A method of transforming variables in a variational data assimilation module using a cubed-sphere grid based on a spectral element method is disclosed. First original meteorological variables are transformed into derivative meteorological variables in a background field of a numerical weather prediction model. A first error correlation between the first original meteorological variables is greater than a second error correlation between the derivative meteorological variables. The derivative meteorological variables are inversely transformed into second original meteorological variables. Values of the second original meteorological variables are adjusted based on variables in an observation field corresponding to the second original meteorological variables. The adjustment of the values of the second original meteorological variables is processed by a transpose of the inverse transformation.

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