RUI: Collaborative Research: Physical Mechanisms Behind the Caribbean Mid-Summer Drought

加勒比区域的雨季呈现出双峰结构，有两个最高峰（5月至6月和9月至10月），中间有所谓的“仲夏”干旱（7月至8月）。 降水量的减少可能是显着的，在7月底和8月初减少了40%。 该地区仲夏干旱的原因一直是个谜，很少有研究调查这种变化的原因。 这一合作研究项目将调查仲夏干旱的发生、持续时间和强度的空间变化，并将这种空间模式与潜在的区域大气过程联系起来，这些区域大气过程嵌入在半球或全球范围内，导致仲夏降雨量减少。 该项目的方法旨在测试两个假设。 第一种假设认为，加勒比仲夏干旱是由三种地方到区域机制共同造成的。 首先，阴影效应（初夏几个月对流产生的云层和降雨阻挡了入射的太阳辐射）导致负反馈，因为表面沃茨冷却抑制了进一步的对流。 太阳辐射减少之后，低层风的反气旋环流引起的辐散风异常，最后，信风的加强由于风的搅动而增加了蒸发。 第二种假设认为，大西洋副热带高压的增强和扩张导致更强的信风，更冷的海面温度和普遍的下沉，导致加勒比地区7月和8月的降雨量减少。 将通过以下方式检验这些假设：（1）利用每月数据评估加勒比仲夏干旱的空间模式，（2）利用每日地面观测和卫星降水和风数据缩小已确定的模式，（3）确定与该现象的发生、持续时间和强度有关的潜在大气过程，和（4）确定全球气候变率和变化的潜在影响，特别是在太平洋（厄尔尼诺）和大西洋发生时，持续时间，加勒比地区国家容易遭受水文干旱造成的自然灾害。 此外，全球气候变化情况表明，加勒比地区今后将面临更大的干旱压力。 这个项目的结果将通过回答这个问题，即为什么加勒比的降雨量在夏季减少，而这个时候预计降雨量会增加，从而扩大加勒比气候学和水文学的知识。 拟议的研究产生的更广泛影响包括为加勒比资源管理人员提供信息，以建立更准确的供水和干旱预测，这是许多岛屿经济活动所必需的。 此外，研究结果将为气候变化科学家提供加勒比区域尺度气候过程的信息，可用于完善海洋-大气环流模型和构建分级尺度模型。 这些模型更有可能提供信息，可供加勒比小岛屿国家用来构建对气候变化情景的现实应对措施。 最后，该项目将通过本科院校研究计划为大量本科生提供服务。

The rainy season in the Caribbean region exhibits a double-peaked structure with two maxima (May-June and September-October) separated by what has been termed a "mid-summer" drought (July-August). The decrease in precipitation can be significant, with as much as a 40 percent decrease in late July and early August. The cause of the region's mid-summer drought has been somewhat of an enigma, with few studies examining the reasons for the variability. This collaborative research project will investigate the spatial variability in the onset, duration, and intensity of the mid-summer drought and link such spatial patterns with potential regional atmospheric processes imbedded within the hemispheric or global context that contribute to the decrease in mid-summer rainfall. The methodology for this project is designed to test two hypotheses. The first hypothesis states that the Caribbean mid-summer drought is created through a combination of three local to regional mechanisms. First, a shadowing effect (cloudiness and rainfall produced by convection in the early summer months block incoming solar radiation) leads to a negative feedback as surface waters cool inhibiting further convection. The decrease in solar radiation then is followed by divergent wind anomalies caused by an anticyclonic circulation of low-level winds, and finally, a strengthening of trade winds increases evaporation due to wind stirring. The second hypothesis states that an intensification and expansion of the Atlantic Ocean sub-tropical high pressure causes stronger trade winds, cooler sea surface temperatures, and general subsidence that result in less Caribbean rainfall in July and August. These hypotheses will be tested through (1) assessment of Caribbean mid-summer drought spatial patterns with monthly data, (2) downscaling of identified patterns with daily surface observations and satellite precipitation and wind data, (3) identification of potential atmospheric processes linked to the onset, duration, and intensity of the phenomenon, and (4) identification of the potential influence of global climate variability and change, particularly over the Pacific (El Nino) and Atlantic upon the onset, duration, and intensity of the Caribbean mid-summer drought.The nations of the Caribbean are prone to natural disasters from hydrologic drought. Further, global climate change scenarios suggest that the Caribbean will experience greater drought stress in the future. The results from this project will expand knowledge of Caribbean climatology and hydrology by answering the question, why does Caribbean rainfall decrease in the summer, a time when precipitation is expected to increase? Broader impacts resulting from the proposed research include providing information for Caribbean resource managers to create more accurate water supply and drought forecasts, a necessity for many island economic activities. In addition, results will provide climate change scientists with information of regional scale climatic processes in the Caribbean that can be used to refine ocean-atmosphere general circulation models and construct hierarchical scale-based models. Such models are more likely to provide information that can be used by Caribbean small island states to construct realistic responses to climate change scenarios. Finally, the project will serve a significant number of undergraduate students through the Research in Undergraduate Institutions program.