Thanh Ngo-Duc

Sensitivity of the Track and Intensity Forecasts of Typhoon Megi (2010) to Satellite-Derived Atmospheric Motion Vectors with the Ensemble Kalman Filter

AbstractIn this study, sensitivities of the track and intensity forecasts of Typhoon Megi (2010) to the Cooperative Institute for Meteorological Satellite Studies (CIMSS) University of Wisconsin satellite atmospheric motion vector (AMV) dataset are examined. Assimilation of the CIMSS AMV dataset using the local ensemble transform Kalman filter implemented in the Weather Research and Forecasting model shows that the AMV data can significantly improve the track forecast of Typhoon Megi, especially the sharp turn from west-northwest to north after crossing the Philippines. By broadening the western Pacific subtropical high to the west, the AMV data can help reduce the eastward bias of the track, thus steering the storm away inimical shear environment and facilitating its subsequent development.Further sensitivity experiments with separated assimilation of the low- to midlevel (800–300 hPa) and upper-level (300–100 hPa) AMV winds reveal that, despite the sparse distribution of the low-level AMV winds with mos...

Evolution of meteorological drought characteristics in Vietnam during the 1961–2007 period

The drought conditions over the seven sub-climatological regions in Vietnam are examined using three meteorological drought indices: de Martonne J, PED, and Standardized Precipitation Index (SPI). According to the seasonal probabilities of drought occurrence estimated by the de Martonne index, droughts mainly occur between November and March in all the sub-regions. The PED index and the SPI index generally show high probabilities of drought occurrence from April to August and from May to October, respectively. In the southern sub-regions of Vietnam, droughts more frequently occur in El Niño years and wet conditions are more frequently observed in La Niña years. However, such El Niño–Southern Oscillation influences are not clearly observed in the northern sub-regions. During 1961–2007, droughts significantly increased in the northern part of Vietnam. In the southern regions, PED shows increasing drought conditions while J and SPI show decreasing drought trends for almost all the stations.

Onset of the Rainy Seasons in the Eastern Indochina Peninsula

AbstractThe onset dates of rainy season over the eastern Indochina Peninsula (8.5°–23.5°N, 100°–110°E) are objectively determined for individual years from 1958 to 2007 using the empirical orthogonal function (EOF) analysis. On average, the onset of the summer rainy season (SRS) determined by EOF1 is 6 May, with a standard deviation of 13 days. The autumn rainy season (ARS) indicated by EOF2 has a mean onset and standard deviation of 16 September and 12 days, respectively. The SRS onset is characterized by the evolution of summer monsoon westerlies and the northward propagation of strong convection from the equatorial region. Conversely, the withdrawal of the summer monsoon over northeastern Indochina in late summer–early autumn favors the ARS onset. Both onsets are strongly associated with intraseasonal oscillation on 30–60- and 10–20-day time scales.Examination of the precursory signals associated with the early/late onsets of both SRS and ARS implies that ENSO has a significant impact on their year-to-...

Quantification of Warming Climate-Induced Changes in Terrestrial Arctic River Ice Thickness and Phenology

AbstractA land process model [the coupled hydrological and biogeochemical model (CHANGE)] is used to quantitatively assess changes in the ice phenology, thickness, and volume of terrestrial Arctic rivers from 1979 to 2009. The CHANGE model was coupled with a river routing and discharge model enabling explicit representation of river ice and water temperature dynamics. Model-simulated river ice phenological dates and thickness were generally consistent with in situ river ice data and landscape freeze–thaw (FT) satellite observations. Climate data indicated an increasing trend in winter surface air temperature (SAT) over the pan-Arctic during the study period. Nevertheless, the river ice thickness simulations exhibited a thickening regional trend independent of SAT warming, and associated with less insulation and cooling of underlying river ice by thinning snow cover. Deeper snow depth (SND) combined with SAT warming decreased simulated ice thickness, especially for Siberian rivers, where ice thickness is m...

High-resolution simulations for Vietnam - methodology and evaluation of current climate

To assist the government of Vietnam in its efforts to better understand the impacts of climate change and prioritise its adaptation measures, dynamically downscaled climate change projections were produced across Vietnam. Two Regional Climate Models (RCMs) were used: CSIRO’s variable-resolution Conformal-Cubic Atmospheric Model (CCAM) and the limited-area model Regional Climate Model system version 4.2 (RegCM4.2). First, global CCAM simulations were completed using bias- and variance-corrected sea surface temperatures as well as sea ice concentrations from six Coupled Model Intercomparison Project Phase 5 (CMIP5) global climate models. This approach is different from other downscaling approaches as it does not use any atmospheric fields from the GCMs. The global CCAM simulations were then further downscaled to 10 km using CCAM and to 20 km using RegCM4.2. Evaluations of temperature and precipitation for the current climate (1980-2000) were completed using station data as well as various gridded observational datasets. The RCMs were able to reproduce reasonably well most of the important characteristics of observed spatial patterns and annual cycles of temperature. Average and minimum temperatures were well simulated (biases generally less than 1oC), while maximum temperatures had biases of around 1oC. For precipitation, although the RCMs captured the annual cycle, RegCM4.2 was too dry in Oct.-Nov. (-60% bias), while CCAM was too wet in Dec.- Mar. (130% bias). Both models were too dry in summer and too wet in winter (especially in northern Vietnam). The ability of the ensemble simulations to capture current climate increases confidence in the simulations of future climate.

Seasonal Prediction of Surface Air Temperature across Vietnam Using the Regional Climate Model Version 4.2 (RegCM4.2)

To investigate the ability of dynamical seasonal climate predictions for Vietnam, the RegCM4.2 is employed to perform seasonal prediction of 2 m mean (T2m), maximum (Tx), and minimum (Tn) air temperature for the period from January 2012 to November 2013 by downscaling the NCEP Climate Forecast System (CFS) data. For model bias correction, the model and observed climatology is constructed using the CFS reanalysis and observed temperatures over Vietnam for the period 1980–2010, respectively. The RegCM4.2 forecast is run four times per month from the current month up to the next six months. A model ensemble prediction initialized from the current month is computed from the mean of the four runs within the month. The results showed that, without any bias correction (CTL), the RegCM4.2 forecast has very little or no skill in both tercile and value predictions. With bias correction (BAS), model predictions show improved skill. The experiment in which the results from the BAS experiment are further successively adjusted (SUC) with model bias at one-month lead time of the previous run showed further improvement compared to CTL and BAS. Skill scores of the tercile probability forecasts were found to exceed 0.3 for most of the target months.

Climate Change in the Coastal Regions of Vietnam

The present chapter provides details on the climate and seasonal differences in the five climatic zones in Vietnam: the Northeast Coast, North Delta Coast, North-Central Coast, South-Central Coast, and South Coast. Based on the daily data collected at 23 meteorological stations, it was shown that during the period 1960–2011, average annual temperatures in the coastal zones of Vietnam increased significantly, by up to 0.28°C per decade in the South Coast. Among the four seasons, winter and spring showed the largest and smallest increase in temperature, respectively. The maximum and minimum daily temperatures also showed upward trends, with a higher increase of the latter variable. Unlike temperature, changes in rainfall varied significantly among regions, with a decreasing tendency in the northern coast and an increasing trend in the central and southern coastal regions. The annual maximum number of consecutive wet days experienced some small changes in the South-Central Coast, though it was almost unchanged in the other coastal regions. Meanwhile, the annual maximum number of consecutive dry days decreased significantly in the South Coast of Vietnam. A variety of different future climate scenarios for the coastal regions of Vietnam are also discussed in this chapter. Two main approaches (namely statistical downscaling and dynamical downscaling) were applied to build future scenarios for Vietnam. Up to the present, there have been four sets of scenarios that have been built for Vietnam, with the level of detail and clarity of approach being upgraded over time: (i) the 1994 scenarios, (ii) the 1998 scenarios, (iii) the 2009 scenarios, and (iv) the updated 2012 scenarios. Among them, details of the methods for building the 1994 and 1998 scenarios were not well documented. The 2009 scenarios applied the statistical downscaling method to provide future changes in mean climate variables under the Special Report on Emissions Scenarios. On the other hand, in the 2012 scenarios, dynamical downscaling results were used together with the statistical ones. The details of the 2012 scenarios are given at the provincial level or even finer. Moreover, the 2012 updates included the projections for some extreme climate indicators, such as maximum temperature, minimum temperature, number of hot days, and maximum daily rainfall.

Evaluation of the NCEP Climate Forecast System and Its Downscaling for Seasonal Rainfall Prediction over Vietnam

AbstractThis study investigates the ability to apply National Centers for Environmental Prediction (NCEP) Climate Forecast System (CFS) products and their downscaling by using the Regional Climate Model version 4.2 (RegCM4.2) on seasonal rainfall forecasts over Vietnam. First, the CFS hindcasts (CFS_Rfc) from 1982 to 2009 are used to assess the ability of the CFS to predict the overall circulation and precipitation patterns at forecast lead times of up to 6 months. Second, the operational CFS forecasts (CFS_Ope) and its RegCM4.2 downscaling (RegCM_CFS) for the period 2012–14 are used to derive seasonal rainfall forecasts over Vietnam. The CFS_Rfc and CFS_Ope are validated against the ECMWF interim reanalysis, the Global Precipitation Climatology Centre (GPCC) analyzed rainfall, and observations from 150 meteorological stations across Vietnam. The results show that the CFS_Rfc can capture the seasonal variability of the Asian monsoon circulation and rainfall distribution. The higher-resolution RegCM_CFS pr...