African Wave Disturbances in the GISS GCM and their Relationship to Climate Variability

标题：GISS GCM中的非洲波扰动及其与气候变率的关系非洲波扰动是北非北部夏季对流层中偏东环流中的波状扰动，它组织了独特的辐合空间格局，并经常形成降水。虽然萨赫勒地区的季节性降水与这些波有关，但GCM关于撒哈拉以南降雨年际变化的研究并未明确考虑它们的影响。这项研究是在初步工作的基础上进行的，该工作在GISS GCM中找到了一个相当现实的非洲波的代表。该项目将研究模式在4 × 5度和2 × 2.5度水平分辨率下的波动行为，以及这种模式行为与非洲夏季风主要环流特征（即热带和非洲东风急流）之间的关系。将根据50年代至80年代选定年份（包括萨赫勒降水异常稀少或丰富的年份）观测到的全球海温强迫模式运行，创建大约10-20个夏季的GCM模拟档案。此外，将从CO2浓度加倍的三个平衡模拟集合中分析波浪特性。对于每一次运行，模式风和降水将被保存为北非方格的6小时平均值。这些数据将用于构建不同地点、月份和年份的风、散度和降水率的波浪复合材料。经向风和降水时间序列的功率谱将显示与非洲波周期有关的谱峰。交叉光谱将记录环流和降水的相互关系，选定光谱振幅的空间制图将突出显示首选活动的地理区域。光谱振幅的复合、光谱、跨谱图以及空间和空间分布的年际变化将反映干旱和强降水以及更温暖的双co2气候情景下波浪行为的变异性。模式结果将与文献中的观测分析和相应的ECMWF每日两次观测风的时间序列分析进行比较。这项研究很重要，因为它试图提高我们模拟和预测气候变化的能力。

ATM-9407018 Druyan, Leonard Columbia University Title: African Wave Disturbances in the GISS GCM and their Relationship to Climate Variability African wave disturbances are wave-like perturbations in the mid- tropospheric easterly circulation of boreal summer over northern Africa which organize distinctive spatial patterns of convergence and often precipitation. Although Sahel seasonal precipitation is associated with these waves, GCM studies of the interannual variability of sub-Saharan rainfall have not explicitly considered their influence. The research is based on preliminary work which found a reasonably realistic representation of African waves in the GISS GCM. The project will study wave behavior in the model at 4x5 degree and 2x2.5 degree horizontal resolution, and the relationship between this modeled behavior and the principal circulation features of the African summer monsoon, namely the tropical and African Easterly Jets. An archive of GCM simulations of some 10-20 summer seasons will be created from model runs forced with observed global SST for selected years during the 1950's through the 1980's (including years of anomalously sparse or abundant Sahel rainfall). In addition, wave characteristics will be analyzed from an ensemble of three equilibrium simulations with doubled CO2 concentration. For each run, model winds and precipitation will be saved as six- hour averages for grid boxes over northern Africa. These data will be used to construct wave composites of winds, divergence and precipitation rates for different locations, months and years. Power spectra of meridional wind and precipitation time series will show the spectral peaks that are related to African wave periodicities. Cross-spectra will document the mutual correlations of circulation and precipitation and spatial mapping of selected spectral amplitudes will highlight the geographical areas of preferred activity. Interannual variations in the composites, spectra, cross-spec tra and spatial and spatial distributions of spectral amplitudes will reflect variability of wave behavior for contrasting scenarios of drought and heavy precipitation and for the warmer, double-CO2 climate. Model results will be compared with analyses of observations in the literature and with analyses of time series of corresponding twice-daily observed ECMWF winds. This research is import because it seeks to increase our ability to simulate and predict climate variability.