Coupled evaluation of below- and aboveground energy and water cycle variables from reanalysis products over five flux tower sites in the United States

William Lytle, Xubin Zeng

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

Reanalysis products are widely used to study the land-atmosphere exchanges of energy, water, and carbon fluxes and have been evaluated using in situ data above or below ground. Here, measurements for several years at five flux tower sites in the United States (with a total of 315 576 h of data) are used for the coupled evaluation of both below- and aboveground processes from three global reanalysis products and six global land data assimilation products. All products show systematic errors in precipitation, snow depth, and the timing of the melting and onset of snow. Despite the biases in soil moisture, all products show significant correlations with observed daily soil moisture for the periods with unfrozen soil. While errors in 2-m air temperature are highly correlated with errors in skin temperature for all sites, the correlations between skin and soil temperature errors are weaker, particularly over the sites with seasonal snow. While net short- and longwave radiation flux errors have opposite signs across all products, the net radiation and ground heat flux errors are usually smaller in magnitude than turbulent flux errors. On the other hand, the all-product averages usually agree well with the observations on the evaporative fraction, defined as the ratio of latent heat over the sum of latent and sensible heat fluxes. This study identifies the strengths and weaknesses of these widely used products and helps understand the connection of their errors in above- versus belowground quantities.

Original languageEnglish (US)
Pages (from-to)2105-2119
Number of pages15
JournalJournal of Hydrometeorology
Volume17
Issue number7
DOIs
StatePublished - 2016

Fingerprint

energy
water
snow
skin
soil moisture
shortwave radiation
evaluation
product
net radiation
longwave radiation
latent heat flux
sensible heat flux
carbon flux
data assimilation
soil temperature
heat flux
air temperature
melting
atmosphere
soil

Keywords

  • Atmosphere-land interaction
  • Models and modeling
  • Observational techniques and algorithms
  • Physical Meteorology and Climatology
  • Reanalysis data
  • Snow cover
  • Surface observations

ASJC Scopus subject areas

  • Atmospheric Science

Cite this

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title = "Coupled evaluation of below- and aboveground energy and water cycle variables from reanalysis products over five flux tower sites in the United States",
abstract = "Reanalysis products are widely used to study the land-atmosphere exchanges of energy, water, and carbon fluxes and have been evaluated using in situ data above or below ground. Here, measurements for several years at five flux tower sites in the United States (with a total of 315 576 h of data) are used for the coupled evaluation of both below- and aboveground processes from three global reanalysis products and six global land data assimilation products. All products show systematic errors in precipitation, snow depth, and the timing of the melting and onset of snow. Despite the biases in soil moisture, all products show significant correlations with observed daily soil moisture for the periods with unfrozen soil. While errors in 2-m air temperature are highly correlated with errors in skin temperature for all sites, the correlations between skin and soil temperature errors are weaker, particularly over the sites with seasonal snow. While net short- and longwave radiation flux errors have opposite signs across all products, the net radiation and ground heat flux errors are usually smaller in magnitude than turbulent flux errors. On the other hand, the all-product averages usually agree well with the observations on the evaporative fraction, defined as the ratio of latent heat over the sum of latent and sensible heat fluxes. This study identifies the strengths and weaknesses of these widely used products and helps understand the connection of their errors in above- versus belowground quantities.",
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author = "William Lytle and Xubin Zeng",
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AU - Zeng, Xubin

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N2 - Reanalysis products are widely used to study the land-atmosphere exchanges of energy, water, and carbon fluxes and have been evaluated using in situ data above or below ground. Here, measurements for several years at five flux tower sites in the United States (with a total of 315 576 h of data) are used for the coupled evaluation of both below- and aboveground processes from three global reanalysis products and six global land data assimilation products. All products show systematic errors in precipitation, snow depth, and the timing of the melting and onset of snow. Despite the biases in soil moisture, all products show significant correlations with observed daily soil moisture for the periods with unfrozen soil. While errors in 2-m air temperature are highly correlated with errors in skin temperature for all sites, the correlations between skin and soil temperature errors are weaker, particularly over the sites with seasonal snow. While net short- and longwave radiation flux errors have opposite signs across all products, the net radiation and ground heat flux errors are usually smaller in magnitude than turbulent flux errors. On the other hand, the all-product averages usually agree well with the observations on the evaporative fraction, defined as the ratio of latent heat over the sum of latent and sensible heat fluxes. This study identifies the strengths and weaknesses of these widely used products and helps understand the connection of their errors in above- versus belowground quantities.

AB - Reanalysis products are widely used to study the land-atmosphere exchanges of energy, water, and carbon fluxes and have been evaluated using in situ data above or below ground. Here, measurements for several years at five flux tower sites in the United States (with a total of 315 576 h of data) are used for the coupled evaluation of both below- and aboveground processes from three global reanalysis products and six global land data assimilation products. All products show systematic errors in precipitation, snow depth, and the timing of the melting and onset of snow. Despite the biases in soil moisture, all products show significant correlations with observed daily soil moisture for the periods with unfrozen soil. While errors in 2-m air temperature are highly correlated with errors in skin temperature for all sites, the correlations between skin and soil temperature errors are weaker, particularly over the sites with seasonal snow. While net short- and longwave radiation flux errors have opposite signs across all products, the net radiation and ground heat flux errors are usually smaller in magnitude than turbulent flux errors. On the other hand, the all-product averages usually agree well with the observations on the evaporative fraction, defined as the ratio of latent heat over the sum of latent and sensible heat fluxes. This study identifies the strengths and weaknesses of these widely used products and helps understand the connection of their errors in above- versus belowground quantities.

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KW - Surface observations

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