Observation analysis of land‐atmosphere interactions over the Loess Plateau of northwest China

Arid and semi-arid areas of the Loess Plateau over northwestern China are one of the dust aerosol source regions featured by its unique underlying surface. These areas, suffering the severe aridity trend in past decades, are also known as the transitional zone of climate and ecosystem change. To better understand the basic characteristics of the land surface energy budget, seasonal and diurnal variations of moisture and heat flux over this region, field observations collected at the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL, 35 degrees 57' N, 104 degrees 08' E, Elev. 1965.8 m) from January 2007 to December 2008 were analyzed systematically, especially focusing on land surface energy partitioning and energy balance. The results indicate that all four radiative components had distinct seasonal and diurnal cycles, except for the diurnal variation of downward longwave radiation. They maintained high values during the growing season and low values during the non-growing season. The highest daily mean value of DSR (downward shortwave radiation, 369.2 Wm(-2)), DLR (downward longwave radiation, 386.8 Wm(-2)) and ULR (upward longwave radiation, 484.2 Wm(-2)) measured in summer while the highest daily mean value of USR (upward shortwave radiation, 150.1 Wm(-2)) occurred in winter as the snow cover. The highest surface albedo was also found in winter as a result of the snow cover. Surface albedo was lower in the growing season (wet season) due to the larger vegetation fraction and wetter soil. The components of the land surface energy budget varied seasonally except for the surface soil heat flux, and all showed strong diurnal cycles. Net radiation increased from winter to summer and decreased from summer to winter associated with the variation of DSR. Sensible (latent) heat flux was the main consumer of the available energy in winter and spring (summer and autumn). The energy imbalance problem was also identified. When the soil heat storage in the surface soil and vegetation canopy was neglected, the energy imbalance ratio was about 22%. While given the surface heat storage calculated by the thermal diffusion equation and correction method (TDEC), the imbalance ratio was only 14%. Furthermore, taking the soil heat storage into account, this ratio was only 8% in spring, and 15% in summer and autumn. Compared with the bare surface layer in spring, it is likely that a part of energy was stored in the vegetation canopy in summer and autumn. In addition, the sensible and latent heat fluxes over different land surface types of the Loess Plateau are analyzed. Sensible and latent heat fluxes are utterly different substantially over those different underlying surfaces due to the factors such as vegetation, precipitation, and soil moisture.

[1]  Dennis D. Baldocchi,et al.  Seasonal variation of energy and water vapor exchange rates above and below a boreal jack pine forest canopy , 1997 .

[2]  Thomas Foken,et al.  Post-Field Data Quality Control , 2004 .

[3]  Xiuji Zhou,et al.  Variation of surface albedo and soil thermal parameters with soil moisture content at a semi-desert site on the western Tibetan Plateau , 2005 .

[4]  M. Rosset.  Seasonal variation in radiation and energy balances of permanent pastures at different altitudes , 1997 .

[5]  Soon-Ung Park,et al.  Turbulence Structure In Unstable Conditions Over Various Surfaces , 2001 .

[6]  K. Davis,et al.  Influence of advection on measurements of the net ecosystem‐atmosphere exchange of CO2 from a very tall tower , 2000 .

[7]  Comparison of water vapour, heat and energy exchanges over agricultural and wetland ecosystems , 2009 .

[8]  R. Dickinson.  LAND-ATMOSPHERE INTERACTION , 1995 .

[9]  Jiemin Wang,et al.  Evaporation from the desert: Some preliminary results of HEIFE , 1992 .

[10]  E. K. Webb,et al.  Correction of flux measurements for density effects due to heat and water vapour transfer , 1980 .

[11]  J. Kutzbach,et al.  Evolution of Asian monsoons and phased uplift of the Himalaya–Tibetan plateau since Late Miocene times , 2001, Nature.

[12]  Michael Bahn,et al.  Seasonal and inter-annual variability of the net ecosystem CO2 exchange of a temperate mountain grassland: effects of climate and management. , 2008, Journal of geophysical research. Atmospheres : JGR.

[13]  Albert A. M. Holtslag,et al.  Flux Parameterization over Land Surfaces for Atmospheric Models , 1991 .

[14]  D. Lenschow,et al.  Seasonal and diurnal variations in moisture, heat and CO 2 fluxes over a typical steppe prairie in Inner Mongolia, China , 2009 .

[15]  Bao Yan.  Review of Land-Atmosphere Interaction Research in Arid and Semi-arid Regions , 2006 .

[16]  Observation and study of land surface parameters over Gobi in typical arid region , 2002 .

[17]  Liangxia Zhang,et al.  Surface energy exchanges above two grassland ecosystems on the Qinghai-Tibetan Plateau , 2009 .

[18]  W. Massman.  A simple method for estimating frequency response corrections for eddy covariance systems , 2000 .

[19]  J. Wilczak,et al.  Sonic Anemometer Tilt Correction Algorithms , 2001 .

[20]  Jiemin Wang,et al.  Turbulence Structure and Transfer Characteristics in the Surface Layer of the HEIFE Gobi Area , 1991 .

[21]  胡隐樵,et al.  黑河实验（HEIFE）—对干旱地区陆面过程的一些新认识 , 1994 .

[22]  Zhang Leiming.  Relationship between the Soil Moisture and the Vegetation Productivity in the Loess Plateau , 2002 .

[23]  W. Massman.  Reply to comment by Rannik on “A simple method for estimating frequency response corrections for eddy covariance systems” , 2001 .

[24]  Jianping Huang,et al.  Surface turbulent flux measurements over the Loess Plateau for a semi-arid climate change study , 2009 .

[25]  Kun Yang,et al.  A temperature prediction-correction method for estimating surface soil heat flux from soil temperature and moisture data , 2008 .

[26]  C. Bernhofer,et al.  Energy balance comparison of the Hartheim forest and an adjacent grassland site during the HartX experiment , 1996 .

[27]  Y. Xue,et al.  The impact of vegetation and soil parameters in simulations of surface energy and water balance in the semi-arid sahel: A case study using SEBEX and HAPEX-Sahel data , 2006 .

[28]  Shuzhen Peng,et al.  Onset of Asian desertification by 22 Myr ago inferred from loess deposits in China , 2002, Nature.

[29]  Zhiqiu Gao,et al.  Seasonal and diurnal variations in moisture, heat, and CO2 fluxes over grassland in the tropical monsoon region of southern China , 2007 .

[30]  Ann Henderson-Sellers,et al.  Evapotranspiration models with canopy resistance for use in climate models, a review , 1991 .

[31]  Frans T. M. Nieuwstadt,et al.  Temperature measurement with a sonic anemometer and its application to heat and moisture fluxes , 1983 .

[32]  Y. Harazono,et al.  Measurement of energy budget components during the International Rice Experiment (IREX) in Japan , 1998 .

[33]  胡隐樵,et al.  SOME NEW UNDERSTANDINGS OF LAND-SURFACE PROCESSES IN ARID AREA FROM THE HEIFE , 1996 .

[34]  Ni Guo,et al.  Variability of soil moisture and its relationship with surface albedo and soil thermal parameters over the Loess Plateau , 2009 .

[35]  C. J. Moore.  Frequency response corrections for eddy correlation systems , 1986 .

[36]  K. Musiake,et al.  Observations of Energy Fluxes and Evapotranspiration over Terrestrial Complex Land Covers in the Tropical Monsoon Environment , 2002 .

[37]  Z. An,et al.  The history and variability of the East Asian paleomonsoon climate , 2000 .

[38]  Congbin Fu,et al.  Initial Science Plan of the Monsoon Asia Integrated Regional Study , 2006 .

[39]  David P. Billesbach,et al.  Spatiotemporal Variations in Growing Season Exchanges of CO2, H2O, and Sensible Heat in Agricultural Fields of the Southern Great Plains , 2007 .

[40]  Chiel C. van Heerwaarden,et al.  Mean and Flux Horizontal Variability of Virtual Potential Temperature, Moisture, and Carbon Dioxide: Aircraft Observations and LES Study , 2008 .

[41]  Thomas Foken,et al.  Workshop on Instrumental and Methodical Problems of Land Surface Flux Measurements , 1995 .

[42]  Start Regional,et al.  The Long-Term Field Experiment on Aridification and the Ordered HumanActivity in Semi-Arid Area at Tongyu, Northeast China , 2004 .

[43]  Lei Zhang,et al.  An overview of the Semi-arid Climate and Environment Research Observatory over the Loess Plateau , 2008 .

[44]  George Burba,et al.  Surface energy fluxes of Phragmites australis in a prairie wetland , 1999 .

[45]  P. Rowntree,et al.  Atmospheric Parameterization Schemes for Evaporation over Land: Basic Concepts and Climate Modeling Aspects , 1991 .