基于EOS/MODIS资料的中国黄土高原西部土地覆盖分类

土地利用和覆盖信息不仅是全球及区域气候模式中所需的重要信息,也是描述生态系统的重要基础数据;获取其现状和变化信息,对于揭示土地覆盖的特征和变化规律,探讨变化的驱动因子,分析评价区域生态环境具有重要现实意义。采用多时相和多光谱遥感资料进行土地覆盖分类已成为一种行之有效的方法。植被类型的差异除了可表现为光谱差异外,还可表现为植被生长规律的差异;植被生长以年为周期,在这个周期内不同植被类型有着各自的生繁衰枯的物候节律,表现出不同的生长规律,其规律性极强,这种规律性也可以作为植被分类的一个出发点。于是,NDVI的时间序列分析成为基于生物气候特征的地表覆盖分类的一种手段。基于MODIS资料,首先对2003年植被生长季内共9个月的NDVI时间序列数据进行离散傅立叶变换,取得该时间序列的均值和前4个频率分量的振幅和相位后;采用ISODATA算法对中国黄土高原西部及其周边地区进行了分层土地覆盖分类,并采用现有的土地覆盖数据集,进行了类别归并和精度评估,分类结果的总体精度达到了81.3%,Kappa系数达到了75.4%,结果证明了这种方法的可行性。     

西藏地区植被覆盖特征与气象因子的相关分析

利用NOAA-AVHRR数据,以归一化植被指数(NDVI)作为植被覆盖特征的指标,研究1982—2000年西藏地区地表植被覆盖的空间分布及时间序列变化,讨论了各季节植被活动的状况。并通过计算不同时段降水量与年最大NDVI、典型区域NDVI与降水、平均温度之间的相关系数,分析了不同植被类型下气象要素与植被覆盖的关系。     

内蒙古植被NDVI变化特征分析

对植被状况和植被覆盖的研究可以反映植被受环境条件影响产生的时空变化。文章根据GIMMS-NDVI数据集1982—2006年影像数据,分析内蒙古农田、森林、草原三种植被类型NDVI年内、年际的变化趋势以及植被覆盖变化特征的空间差异。各植被类型变化曲线都呈现4—7月NDVI激增,8—10月NDVI猛降,冬季农田、草原植被覆盖接近裸土的特点。农田夏季NDVI平均值的历年线性变化趋势通过显著性检验,森林夏季NDVI平均值呈现下降的趋势,草原夏季NDVI平均值呈现上升的趋势,但都不显著。     

西北地区MODIS-NDVI指数饱和问题分析

为了了解西北地区MODIS-NDVI和MODIS-EVI两种植被指数的特点,本文利用美国NASA LP DAAC(Land Process Distributed Active Archive Center)2004年1~12月的250 m分辨率16天植被指数合成的MOD13 Q1数据集,对西北地区不同类型植被NDVI和EVI的特征进行分析,并对西北地区MODIS-NDVI饱和问题进行了初步研究。结果表明:NDVI和EVI对干旱—半干旱气候区植被覆盖度不高的植被类型描述能力相似,月际变化趋势一致。西北地区各种植被类型NDVI比EVI高,NDVI与EVI的差异总体上呈现从半荒漠、草原、农区到林区,随NDVI值的增加而增大的规律。对植被度覆盖度高的阔叶林和针叶林,在植被生长旺盛期,NDVI总在0.8附近波动,NDVI随植被的生长增加的很小,一直维持在一个高且平的范围内,不再能看出植被生长变化的现象,即饱和现象严重;而EVI表现良好,随着植被的生长而增加,能明显地反映出植被生长的季节变化。西北高寒草甸和陕西关中农业区NDVI也出现有不同程度的饱和,饱和时间因植被的不同从1~2月不等。0.8可作为NDVI饱和的阈值。NDVI饱和问题对卫星监测植被的研究和应用会产生误差,EVI能较好地解决NDVI的饱和问题。     

大兴安岭植被NDVI变化及其对气候的响应

利用S-G(Savitsky-Golay)滤波对2000—2016年呼伦贝尔市境内的大兴安岭植被NDVI序列进行逐栅格重构并剔除突变点,结合大兴安岭海拔、坡向、坡度等地理因子和气温、降水等气象因子,分析大兴安岭植被生长季NDVI的变化及其对气候的响应。结果表明:大兴安岭植被NDVI生长季均值呈上升趋势,平均增速为0. 029/10 a。植被NDVI随海拔的增加呈现先缓慢减小后迅速增加的趋势,随坡向变化不大,随坡度的增加而增加。植被NDVI的生长季均值与1 a前和2 a年前的降水呈现显著的正相关,具有明显的滞后性。在每年植被恢复生长初期各海拔植被均与气温呈现极显著的正相关,年内植被NDVI与降水的相关性在垂直方向上存在较大差异。     

天山巴音布鲁克草原植被变化及其与气候因子的关系

利用1982-2000年逐月NOAA/AVHRR NDVI的时间序列数据,分析了天山巴音布鲁克草原植被覆盖的动态变化及其与降水、气温、浅层地温等气候因子的关系。结果表明：近20 a来巴音布鲁克草原植被覆盖面积总体上呈现增加趋势,生态环境有所改善。同时,生长季（4-9月）NDVI与降水、气温和浅层地温的相关分析表明, 气温和浅层地温是影响巴音布鲁克草原植被生长的两个重要因子。     

春末夏初青藏高原地表植被对全球变暖的响应特征

利用1982年～2002年Pathfinder NDVI遥感数据,采用REOF和倾向度趋势分析方法,研究了5～6月青藏高原地表植被的区域变化特征及时间变化趋势。21a来高原区域植被总体呈增加趋势,但这种变化趋势有着明显的时间和空间差异。表现为5～6月空间上存在一个位于高原南北的两条呈带状分布的植被显著变化区域。该区域内植被对前期气温变化响应迅速,生物量随气温升高呈现出显著的一致增加趋势,增长速率大都超过10%/10a,与前期4～5月全球平均气温相关系数达到0.71,是全球变暖响应的敏感区。进一步的分析表明这种对全球变暖响应的区域差异主要来自于植被分布的不同,植被变化显著的区域基本上处于高山山脉或半荒漠地区NDVI值低于0.12的本底植被覆盖较低的区域。从植被覆盖类型看,草地植被生物量随全球变暖增幅明显,21a约增加10%,对全球变暖响应明显,而中高覆盖区植被和其他类型植被随气温升高的增幅较小,对全球变暖响应较弱。     

基于MODIS NDVI的广西西南典型生态区植被变化对比监测

利用2001—2010年MODIS NDVI逐16 d合成数据对广西十万大山和桂西岩溶山地两个典型生态区植被进行对比监测,分析植被年内变化特征及年际变化趋势。利用同时期的气温和降水量数据,分析两个典型生态区植被NDVI对气温和降水量的响应差异。结果表明:十万大山和桂西岩溶山地生态区年内MODIS NDVI变化特征相似,均表现出"夏秋高,冬春低"的趋势,其中十万大山生态区植被覆盖相对稳定,季节变化较小。近10 a来两个生态区植被均以改善为主,植被改善面积与退化面积比例均约为3∶2。植被年际变化幅度较小,长势较稳定。降水量、平均气温与十万大山生态区植被NDVI的相关性总体上好于桂西岩溶山地生态区,两个生态区植被与降水的相关性较一致。在夏季多表现为负相关,春、秋、冬3季多表现为正相关,这与广西降水时段集中且强度较大的特点有关。由于植被类型的显著差异,两个生态区与气温的相关性具有显著差异。     

乌鲁木齐地区生长季NDVI序列影像的植被覆盖变化分析’

应用EOS／MODIS—Terra卫星数据,按照NDVI(归一化植被指数)最大值合成法计算了乌鲁木齐地区2007、2010年生长季逐旬植被NDVI序列,得到植被长势演变图和植被指数分布基础数据,结合气象资料和南山中山带牧草监测站实测数据,分析了NDVI在乌鲁木齐地区的变化特点及其与气候因子的关系。结果表明：气温、降水是NDVI变化的主要驱动因子,但植被对于气候因子的响应普遍存在滞后性。乌鲁木齐地区NDVI旬最大值总体变化在0．46～0．83范围内。与近10 a中植被长势最好的2007年同期数据比较,2010年春季植被指数比2007年推迟4旬达到0．7以上,表明植被发育期比2007年推迟10～15 d;秋季植被指数7月中旬就出现下降拐点,表明植被发育期比2007年提前4旬进入种子成熟、黄枯期或停止生长。以上结论与南山中山带牧草监测站实测结果相符。     

江西省降水与不同时空尺度下植被NDVI关系研究

利用NASA/AVHRR的982—2006年NDVI(Normalized Difference Vegetation Index)数据和江西省79个气象站1982—2005年逐日降水观测资料,分析了江西省植被和降水的时空变化特征以及年降水和不同时空尺度的植被NDVI间相关关系。结果发现:1)降水在季节和年尺度上变化均不明显;年植被NDVI未发生显著变化,春季植被NDVI呈显著上升趋势,夏、冬两季呈显著下降趋势。2)当植被NDVI的空间尺度达到9×9(即36 km×36 km,可称为"最优时空尺度")时,二者相关系数基本稳定,说明年降水和该空间尺度植被的关系能较好地反映出降水与植被的相互关系。3)各季节降水与不同时空尺度下植被NDVI关系表现为除秋季外,其他3个季节的降水均与植被NDVI显著相关,但与之对应的植被NDVI"最优时空尺度"不尽相同。因此,考虑到不同时空尺度的植被NDVI与降水之间关系存在较大差异,在今后研究二者之间关系时,必须充分考虑时空尺度对研究可能带来的不确定性。     

CHARACTERISTICS AND TRENDS OF CLIMATIC EXTREMES IN CHINA DURING 1959–2014

The spatial and temporal variations of daily maximum temperature(Tmax), daily minimum temperature(Tmin), daily maximum precipitation(Pmax) and daily maximum wind speed(WSmax) were examined in China using Mann-Kendall test and linear regression method. The results indicated that for China as a whole, Tmax, Tmin and Pmax had significant increasing trends at rates of 0.15℃ per decade, 0.45℃ per decade and 0.58 mm per decade,respectively, while WSmax had decreased significantly at 1.18 m·s~(-1) per decade during 1959—2014. In all regions of China, Tmin increased and WSmax decreased significantly. Spatially, Tmax increased significantly at most of the stations in South China(SC), northwestern North China(NC), northeastern Northeast China(NEC), eastern Northwest China(NWC) and eastern Southwest China(SWC), and the increasing trends were significant in NC, SC, NWC and SWC on the regional average. Tmin increased significantly at most of the stations in China, with notable increase in NEC, northern and southeastern NC and northwestern and eastern NWC. Pmax showed no significant trend at most of the stations in China, and on the regional average it decreased significantly in NC but increased in SC, NWC and the mid-lower Yangtze River valley(YR). WSmax decreased significantly at the vast majority of stations in China, with remarkable decrease in northern NC, northern and central YR, central and southern SC and in parts of central NEC and western NWC. With global climate change and rapidly economic development, China has become more vulnerable to climatic extremes and meteorological disasters, so more strategies of mitigation and/or adaptation of climatic extremes,such as environmentally-friendly and low-cost energy production systems and the enhancement of engineering defense measures are necessary for government and social publics.     

ANALYSIS OF “BIMODAL PATTERN” STORM ACTIVITY CHARACTERISTICS OF THE BAY OF BENGAL

Storms that occur at the Bay of Bengal (BoB) are of a bimodal pattern, which is different from that of the other sea areas. By using the NCEP, SST and JTWC data, the causes of the bimodal pattern storm activity of the BoB are diagnosed and analyzed in this paper. The result shows that the seasonal variation of general atmosphere circulation in East Asia has a regulating and controlling impact on the BoB storm activity, and the “bimodal period” of the storm activity corresponds exactly to the seasonal conversion period of atmospheric circulation. The minor wind speed of shear spring and autumn contributed to the storm, which was a crucial factor for the generation and occurrence of the “bimodal pattern” storm activity in the BoB. The analysis on sea surface temperature (SST) shows that the SSTs of all the year around in the BoB area meet the conditions required for the generation of tropical cyclones (TCs). However, the SSTs in the central area of the bay are higher than that of the surrounding areas in spring and autumn, which facilitates the occurrence of a “two-peak” storm activity pattern. The genesis potential index (GPI) quantifies and reflects the environmental conditions for the generation of the BoB storms. For GPI, the intense low-level vortex disturbance in the troposphere and high-humidity atmosphere are the sufficient conditions for storms, while large maximum wind velocity of the ground vortex radius and small vertical wind shear are the necessary conditions of storms.     

LOW-FREQUENCY CIRCULATION AND EXTENDED-RANGE FORECAST IN CONNECTION WITH AUTUMN EXTREME HEAVY RAINFALL PROCESS IN HAINAN

Observed daily precipitation data from the National Meteorological Observatory in Hainan province and daily data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis-2 dataset from 1981 to 2014 are used to analyze the relationship between Hainan extreme heavy rainfall processes in autumn (referred to as EHRPs) and 10–30 d low-frequency circulation. Based on the key low-frequency signals and the NCEP Climate Forecast System Version 2 (CFSv2) model forecasting products, a dynamical-statistical method is established for the extended-range forecast of EHRPs. The results suggest that EHRPs have a close relationship with the 10–30 d low-frequency oscillation of 850 hPa zonal wind over Hainan Island and to its north, and that they basically occur during the trough phase of the low-frequency oscillation of zonal wind. The latitudinal propagation of the low-frequency wave train in the middle-high latitudes and the meridional propagation of the low-frequency wave train along the coast of East Asia contribute to the ‘north high (cold), south low (warm)’ pattern near Hainan Island, which results in the zonal wind over Hainan Island and to its north reaching its trough, consequently leading to EHRPs. Considering the link between low-frequency circulation and EHRPs, a low-frequency wave train index (LWTI) is defined and adopted to forecast EHRPs by using NCEP CFSv2 forecasting products. EHRPs are predicted to occur during peak phases of LWTI with value larger than 1 for three or more consecutive forecast days. Hindcast experiments for EHRPs in 2015–2016 indicate that EHRPs can be predicted 8–24 d in advance, with an average period of validity of 16.7 d.     

AN ATTRIBUTION ANALYSIS OF CHANGES IN POTENTIAL EVAPOTRANSPIRATION IN THE BEIJING–TIANJIN–HEBEI REGION UNDER CLIMATE CHANGE

Based on the measurements obtained at 64 national meteorological stations in the Beijing–Tianjin–Hebei (BTH) region between 1970 and 2013, the potential evapotranspiration (ET0) in this region was estimated using the Penman–Monteith equation and its sensitivity to maximum temperature (Tmax), minimum temperature (Tmin), wind speed (Vw), net radiation (Rn) and water vapor pressure (Pwv) was analyzed, respectively. The results are shown as follows. (1) The climatic elements in the BTH region underwent significant changes in the study period. Vw and Rn decreased significantly, whereas Tmin, Tmax and Pwv increased considerably. (2) In the BTH region, ET0 also exhibited a significant decreasing trend, and the sensitivity of ET0 to the climatic elements exhibited seasonal characteristics. Of all the climatic elements, ET0 was most sensitive to Pwv in the fall and winter and Rn in the spring and summer. On the annual scale, ET0 was most sensitive to Pwv, followed by Rn, Vw, Tmax and Tmin. In addition, the sensitivity coefficient of ET0 with respect to Pwv had a negative value for all the areas, indicating that increases in Pwv can prevent ET0 from increasing. (3) The sensitivity of ET0 to Tmin and Tmax was significantly lower than its sensitivity to other climatic elements. However, increases in temperature can lead to changes in Pwv and Rn. The temperature should be considered the key intrinsic climatic element that has caused the "evaporation paradox" phenomenon in the BTH region.     

Could the Recent Taal Volcano Eruption Trigger an El Ni?o and Lead to Eurasian Warming?

正The Taal Volcano in Luzon is one of the most active and dangerous volcanoes of the Philippines. A recent eruption occurred on 12 January 2020(Fig. 1a), and this volcano is still active with the occurrence of volcanic earthquakes. The eruption has become a deep concern worldwide, not only for its damage on local society, but also for potential hazardous consequences on the Earth's climate and environment.     

Revisiting the Concentration Observations and Source Apportionment of Atmospheric Ammonia

正While China’s Air Pollution Prevention and Control Action Plan on particulate matter since 2013 has reduced sulfate significantly, aerosol ammonium nitrate remains high in East China. As the high nitrate abundances are strongly linked with ammonia, reducing ammonia emissions is becoming increasingly important to improve the air quality of China. Although satellite data provide evidence of substantial increases in atmospheric ammonia concentrations over major agricultural regions, long-term surface observation of ammonia concentrations are sparse. In addition, there is still no consensus on     

COMPARATIVE ANALYSIS OF VARIOUS DATA OF AIR–SEA TEMPERATURE DIFFERENCE AND ITS VARIATION ACROSS SOUTH CHINA SEA IN THE PAST 35 YEARS

Using the International Comprehensive Ocean-Atmosphere Data Set(ICOADS) and ERA-Interim data, spatial distributions of air-sea temperature difference(ASTD) in the South China Sea(SCS) for the past 35 years are compared,and variations of spatial and temporal distributions of ASTD in this region are addressed using empirical orthogonal function decomposition and wavelet analysis methods. The results indicate that both ICOADS and ERA-Interim data can reflect actual distribution characteristics of ASTD in the SCS, but values of ASTD from the ERA-Interim data are smaller than those of the ICOADS data in the same region. In addition, the ASTD characteristics from the ERA-Interim data are not obvious inshore. A seesaw-type, north-south distribution of ASTD is dominant in the SCS; i.e., a positive peak in the south is associated with a negative peak in the north in November, and a negative peak in the south is accompanied by a positive peak in the north during April and May. Interannual ASTD variations in summer or autumn are decreasing. There is a seesaw-type distribution of ASTD between Beibu Bay and most of the SCS in summer, and the center of large values is in the Nansha Islands area in autumn. The ASTD in the SCS has a strong quasi-3a oscillation period in all seasons, and a quasi-11 a period in winter and spring. The ASTD is positively correlated with the Nio3.4 index in summer and autumn but negatively correlated in spring and winter.     

Information for Authors

正AIMS AND SCOPE Atmospheric and Oceanic Science Letters (AOSL) publishes short research letters on all disciplines of the atmosphere sciences and physical oceanography. Contributions from all over the world are welcome.SUBMISSIONAll submitted     

Information for Authors

AIMS AND SCOPE Atmospheric and Oceanic Science Letters （AOSL） pub- lishes short research letters on all disciplines of the atmos- phere sciences and physical oceanography. Contributions from all over the world are welcome.