Spatial distribution and intensity variation characteristics of land-atmosphere coupling in the Northern Hemisphere over the past 70 years

doi:10.11755/j.issn.1006-7639-2025-03-0339

Abstract

Abstract:

Land-atmosphere coupling is a crucial link in the exchange of mass and energy between the land surface and the atmosphere. Water vapor from soil evaporation condenses and releases latent heat during rising and cooling processes, which warms the boundary layer air and reduces atmospheric boundary layer stability, thereby promoting the initiation and development of convection, and can potentially lead to precipitation formation. An in-depth study of the spatio-temporal variation characteristics of land-atmosphere coupling is of great significance for understanding its role in global climate change. Based on the soil moisture data from the Global Land Data Assimilation System (GLDAS), the land surface reanalysis data of the European Centre for Medium-Range Weather Forecasts (ERA5-Land), and the precipitation data from the Global Precipitation Climatology Centre (GPCC) from 1950 to 2020, this study employs three land-atmosphere coupling indices: λ (reflecting the feedback efficiency of soil moisture on precipitation), I_SM-LH (representing the sensitivity of latent heat flux response to soil moisture changes), and I_LH-Pr (representing the sensitivity of precipitation response to latent heat flux changes) to calculate the land-atmosphere coupling strength and identify key coupling regions in the Northern Hemisphere. On this basis, the spatio-temporal characteristics of land-atmosphere coupling in the Northern Hemisphere are analyzed. The results show that the land-atmosphere coupling index I_SM-LH calculated from soil moisture and latent heat flux, can best represent the coupling strength. There are five key land-atmosphere coupling regions in the Northern Hemisphere, namely the North America key coupling region (NA), the Mediterranean key coupling region (MS), the Central Asia-Mongolia key coupling region (CM), the Africa key coupling region (AF), and the South Asia key coupling region (SA). The extent of the key land-atmosphere coupling regions is widest and their coupling strength is strongest in summer, followed by spring. The lagged coupling strength between spring and summer is weaker than the concurrent coupling strength in spring or summer. During the period of 1950-2020, the coupling strength in key land-atmosphere coupling regions exhibited clear linear trends. The NA, SA, and AF key regions showed a linear weakening trend in land-atmosphere coupling strength, with the weakening trend in AF in summer being the most pronounced at the rate of -3.61/10 a (p<0.01). Conversely, the MS and CM key regions showed a strengthening trend, with the linear strengthening trend in CM in summer being the most significant at the rate of 2.28/10 a (p<0.01). The linear trends of coupling strength and precipitation showed an inverse phase relationship in the NA and MS key regions, and an in-phase relationship in the AF and SA key regions. During the same period, anomalies in land-atmosphere coupling strength and precipitation within these key coupling regions showed a significant negative correlation. The negative correlation was strongest in MS in spring, r=-0.469 (p<0.01), and strongest in AF during summer, r=-0.821 (p<0.01).

Key words: land-atmosphere coupling, soil moisture, latent heat flux, precipitation, the Northern Hemisphere

摘要： 陆气耦合是地表与大气之间物质能量交换的重要一环，深入研究陆气耦合的时空变化特征，对认识陆气耦合在全球气候变化中的作用有重要意义。基于1950—2020年全球陆面数据同化系统（Global Land Data Assimilation System，GLDAS）土壤湿度、欧洲中期天气预报中心陆面再分析数据集（ERA5-Land）和全球降水气候中心（Global Precipitation Climatology Centre，GPCC）的降水数据，计算反映土壤水分对降水的反馈（λ）、潜热通量对土壤湿度的变化响应程度（I_SM_-_LH）和降水对地表潜热通量变化响应程度（I_LH_-Pr）的3种陆气耦合指数，从不同角度分析北半球陆气耦合强度及其空间分布特征，确定北半球陆气耦合关键区。在此基础上，分析过去近70 a北半球陆气耦合的时空变化特征。结果表明，I_SM_-_LH能较好地反映土壤湿度-蒸发耦合过程，对陆气耦合强度代表性最好。北半球有5个陆气耦合关键区，分别为北美耦合关键区（NA）、地中海耦合关键区（MS）、中亚-蒙古耦合关键区（CM）、非洲耦合关键区（AF）和南亚耦合关键区（SA）。夏季陆气耦合关键区的范围最广、耦合强度最强，春季次之。春夏之间的前后期耦合强度弱于春、夏季同期的耦合强度。1950—2020年陆气耦合关键区年耦合强度具有明显的线性变化趋势，NA、SA、AF关键区陆气耦合强度呈现减弱趋势，其中AF夏季减弱趋势最明显，气候倾向率为-3.61/10 a（p<0.01）；MS和CM的陆气耦合强度呈现增强趋势，其中CM夏季的线性变化趋势最明显，气候倾向率为2.28/10 a（p<0.01）。在耦合关键区，陆气耦合强度和降水的线性变化趋势在NA和MS呈反相变化，在AF和SA为同相变化；同期的陆气耦合强度异常与降水异常呈显著负相关，春季的负相关在MS最显著（r=-0.469，p<0.01），夏季的负相关在AF最显著（r=-0.821，p<0.01）。

关键词: 陆气耦合, 土壤湿度, 潜热通量, 降水, 北半球

CLC Number:

P461

WANG Chenghai, SHANG Junxiang, ZHANG Feimin, YANG Kai. Spatial distribution and intensity variation characteristics of land-atmosphere coupling in the Northern Hemisphere over the past 70 years[J]. Journal of Arid Meteorology, 2025, 43(3): 339-354.

王澄海, 尚君翔, 张飞民, 杨凯. 北半球近70 a陆气耦合空间分布及其强度变化特征[J]. 干旱气象, 2025, 43(3): 339-354.

Figures/Tables 12

Fig.1 Spatial distribution of the land-atmosphere coupling index λ over the Northern Hemisphere during the period of 1950-2020（a） spring，（b） summer，（c） cross-seasonal （spring to summer）（The diagonal area passes the significance test at 0.05， the black box area represents the key area of land-atmosphere coupling）

Fig.2 Spatial distribution of the land-atmosphere coupling index ISM-LH over the Northern Hemisphere during the period of 1950-2020 （Unit： W·m-2）（a） spring，（b） summer，（c） cross-seasonal （spring to summer）

Fig.3 Spatial distribution of the land-atmosphere coupling index ILH-Pr over the Northern Hemisphere during the period of 1950-2020 （Unit： mm/mon）（a） spring，（b） summer，（c） cross-seasonal （spring to summer）

Fig.4 The locations of key regions of land-atmosphere coupling over the Northern Hemisphere in spring and summer （a） and during spring to summer （b） from 1950 to 2020， as well as the spatial distribution of drought index climate state from 1991 to 2020 （c）

Fig.5 Interannual variation of spring land-atmosphere coupling intensity and precipitation in five land-atmosphere coupling key areas from 1950 to 2020 （The blue （red） histogram is the standardized precipitation （coupling index）， the blue （red） dotted line is the linear trend of precipitation （coupling index）， and the blue （red） broken line is the 9-year moving average of precipitation （coupling indexes）， the same as below）

Fig.6 Interannual variation of summer land-atmosphere coupling intensity and precipitation in five land-atmosphere coupling key areas from 1950 to 2020

Fig.7 Interannual variation of spring-summer land-atmosphere coupling intensity and summer precipitation in three land-atmosphere coupling key areas from 1950 to 2020

Tab.1 Correlation coefficients between the land-atmosphere coupling intensity and precipitation in the Northern Hemisphere

时段	NA	MS	CM	AF	SA
春季	-0.350**	-0.469**	-0.211*	-0.164	-0.335**
夏季	-0.580**	0.071	-0.301**	-0.821**	-0.217*
春夏之间	-0.156		0.044	-0.167

Fig.8 The 500 hPa geopotential height regressed by the index of land-atmosphere coupling strength over the Northern Hemisphere in spring during 1950-2020 （Unit： gpm）（the diagonal area passing the significance test at 0.05，the same as below）

Fig.10 The 500 hPa geopotential height regressed by the index of land-atmosphere coupling strength between spring and summer over the Northern Hemisphere during 1950-2020 （Unit： gpm）

Fig.9 The 500 hPa geopotential height regressed by the index of land-atmosphere coupling strength over the Northern Hemisphere in summer during 1950-2020 （Unit： gpm）

Fig.11 Diagram of the relationship between the land-atmosphere coupling intensity and precipitation in the land-atmosphere coupling key areas

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