This study presents the application of K-means clustering to satellite-based solar irradiation in different regions of Vietnam. The solar irradiation products derived from the Himawari-8 satellite, named AMATERASS by the solar radiation consortium under the Japan Science and Technology Agency (JST), are validated with observations recorded at 5 stations in the period from October 2017 to September 2018 before their use for clustering. High correlations among them enable the use of satellite-based daily global horizontal irradiation (GHI) for spatial variability analysis and regionalization. With respect to the climate regime in Vietnam, the defined 6-cluster groups demonstrate better agreement with the conventionally classified 7 climatic zones rather than the 4 climatic zones of the Köppen classification. The spatial distribution and seasonal variation in the regionalized solar irradiation reflect interchangeable influences of large-scale atmospheric circulation in terms of the East Asian winter monsoon and the South Asian summer monsoon as well as the effect of local topography. Higher daily averaged solar radiation and its weaker seasonal variation were found in two clusters in the southern region where the South Asian summer monsoon dominates in the rainy season. Pronounced seasonal variability in solar irradiation in four clusters in the northern region is associated with the influence of the East Asian monsoon, resulting in its clear reduction during the winter months.
Abstract. According to Krishnamurti , improvements of physical parameterizations will mainly affect simulations for the tropics [10] . The study of William A. Gallus Jr . showed that the higher the model resolution and more detailed convective parameterizations, the better the skill in quantitative precipitation forecast (QPF) in general [16]. The quality of precipitation forecast is so sensitive to convective parameterization scheme (CPS) used in the model as well as model resolution. The fact shows that for high resolution regional model like H14-31 CPS based on low-level moisture convergence as Tiedtke did not give good heavy rainfall forecast in Vietnam . In this paper we used the scheme of Betts-Miller-Janjic (BMJ) based on the convective adjustment toward tropical observationally structures in reality instead of Tiedtke in Hl4-31. Statistical verification results and verification using CRA method of Hl4-31 of two CPSs for seperated cases and for three rain seasons (2003)(2004)(2005) shows that heavy rainfall forecast of Hl4-31/BMJ is better than one of H14-31/TK for Vietnam-South China Sea. CRA verification also shows that it is possible to say that heavy rainfall forecast skill of l-I14-31/BMJ in tropics is nearly similar to the skill of LAPS of Australia.
116Mối quan hệ giữa lượng mây và bức xạ sóng dài đi ra tại đỉnh khí quyển trên khu vực Nam Bộ Tóm tắt: Dựa trên số liệu OLR và lượng mây có độ phân giải 1,0×1,0 độ kinh vĩ của NCEP/NCAR trong thời kì 1981 -2012, mối quan hệ giữa lượng mây và bức xạ sóng dài đi ra tại đỉnh khí quyển (OLR) trên khu vực Nam Bộ đã được xem xét thông qua việc phân tích, so sánh đặc điểm phân bố không gian, biến đổi theo thời gian và mối quan hệ tương quan giữa chúng. Kết quả cho thấy rằng, đặc điểm phân bố và diễn biến trong năm của lượng mây và OLR là ngược nhau, khu vực hoặc thời gian có lượng mây lớn thì OLR nhỏ và ngược lại. Trên khu vực Nam Bộ, OLR thường có giá trị lớn trong mùa khô và trong các năm El Nino, song trong các năm La Nina và trong mùa mưa thì lại có giá trị nhỏ. Trong thời kỳ 1981-2012, OLR trên khu vực có xu thế giảm khoảng 3,6 W/m 2 /thập kỉ, còn lượng mây lại có xu thế tăng khoảng 0,2%/thập kỉ. Từ khóa: Lượng mây, bức xạ sóng dài đi ra, Nam Bộ.Abstract: Using 1,0 0 ×1,0 0 resolution data of the Outgoing Longwave Radiation (OLR) and the cloud cover from NCEP/NCAR during the 1981 -2012 period, the relationship between the cloud cover and the OLR in the Southern of Vietnam was investigated by analyzing and comparing the spatial distribution, temporal evolution and their correlation. The results show that the characteristics of the spatial distribution and the year cycle of cloud cover and OLR are inversely correlated. The region or time that the cloud cover is great, the OLR is small and vice versa. In the Southern of Vietnam, the OLR value is largest (or smallest) in the dry (or rainy) season and in the El-Nino (La-Nina) years. In addition, during the 1981-2012period, the OLR in this region shows a downward trend about 3.6 W/m2/decade, while the cloud cover tends to increase by 0.2%/decade.
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