不同地转速度对季风分布及强度影响的数值模拟

Numerical Simulations of the Monsoon Distribution and Intensity at Different Rotation Rates of the Earth

本文利用风场标准化季节变率指数来探讨不同地转速度或自转周期下,全球季风的水平和垂直分布特征以及其随自转周期的不同而发生的规律性变化,同时探讨了经、纬向风的季节反向对季风区显著分布的影响。此外,定义一个新的表征季节变化相对大小的指数来探讨不同自转周期下,风场季节变化相对于地球自转周期条件下的强度的相对大小。结果表明,在水平方向上,经典的季风区随着自转周期的变化而有所不同;相对实际地球大气而言,在快转条件下,风场季节变率指数显著区在纬圈上呈带状分布,且随自转周期增大,其范围有逐渐减小的趋势;而在慢转条件下,则呈现区域片状甚至经向带状分布,且随自转周期增大,其范围有逐渐增大的趋势。在垂直方向上,在快转条件下,近地面的风场季节变率指数显著区分布比较凌乱,而慢转条件下,则分布比较规则,主要集中在赤道及副热带地区上空,且北半球分布范围更广泛。100hPa高度以下和500hPa高度之上,风场季节变率指数显著区主要分布在南、北纬30°之间,其南北宽度和高值中心的强度随自转周期的改变存在一个规律性变化;100hPa高度以上,在相对快转条件下,风场季节变率指数显著区呈南北对称分布,且主要分布在赤道及副热带地区上空,高值中心强度随自转周期规律性变化,而相对慢转条件下,显著区范围显著减小甚至消失。此外,在相对快转条件下,纬向东、西风带的季节反向是造成风场季节变率指数显著分布的直接原因,而相对慢转条件下,尤其是对流层中上层100hPa高度以下,经向风的季节反向是造成风场季节变率指数显著分布的主要原因。另外,在相对快转条件下,风场季节变化相对大小的高值区主要分布在热带赤道上空的整层大气,而相对慢转条件下,其高值区广泛分布,且随着自转周期逐渐增大,在100hPa高度之上高值区逐渐向南北极缩小甚至消失。

Characteristics and regular variabilities at different rotation rates are discussed for the horizontal and vertical distributions of the global monsoon by the Dynamical Normalized Seasonality（DNS）.Effects of the seasonal changes of meridional and longitudinal wind directions on monsoon areas are also analyzed.Furthermore,a new index is defined to discuss relative seasonal change of wind at different rotation rates compared to the Earth rotation rate.It is showed that typical monsoon areas change with different rotation rates.Horizontally,the DNS is remarkable in the zonal direction at fast rotation rates,and the monsoon areas become smaller and smaller with rotation period increasing.However,at slow rotation rates the DNS is remarkable locally in the meridional direction,and the monsoon areas become larger and larger as the rotation period becomes longer.Vertically,the remarkable DNS distributes irregularly near the surface at fast rotation rates,which is mainly in the equatorial and tropical areas at slow rotation rates with a larger area in the Northern Hemisphere than in the Southern Hemisphere.At levels above 100 hPa and below 500 hPa,the remarkable DNS areas are mainly between 30°S and 30°N,whose intensity and north-to-south width vary regularly with different rotation periods.Above 100 hPa,the remarkable DNS areas,whose maximum intensity changes regularly with different rotation periods,are primarily in the equatorial and subtropical areas with hemispherical symmetrical pattern at fast rotation rates,while they decrease markedly and even disappear at slow rotation rates.Besides,seasonal difference of the zonal wind is the main reason for the remarkable DNS at fast rotation rates.But the seasonal difference of meridional winds causes remarkable DNS at slow rotation rates especially blow 100 hPa.Otherwise,the relative seasonal change of wind at fast rotation rates compared to the Earth rotation rate is remarkable primarily above the equatorial and tropical areas,and the remarkable change areas distribute widely at slow rotation rates and become smaller and smaller above 100 hPa.with the rotation period increasing.