|GUILLOD, B.P. - Eth Zurich
|ORLOWSKY, B. - Eth Zurich
|MIRALLES, D. - University Of Bristol
|TEULING, A.J. - Wageningen University
|BLANKEN, P. - University Of Colorado
|BUCHMANN, N. - Eth Zurich
|CIAIS, P. - National Council For Scientific Research-Cnrs
|EK, M. - Institut De Biologie Integrative De La Cellule
|FINDELL, K.L. - National Oceanic & Atmospheric Administration (NOAA)
|GENTINE, P. - University Of Princeton
|LINTNER, B. - Rutgers University
|Scott, Russell - Russ
|VAN DEN HURK, B. - Royal Netherlands Society For Agricultural Science (KLV)
|SENEVIRATNE, S.I. - Eth Zurich
Submitted to: Atmospheric Chemistry and Physics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/3/2014
Publication Date: 8/20/2014
Citation: Guillod, B., Orlowsky, B., Miralles, D., Teuling, A., Blanken, P., Buchmann, N., Ciais, P., Ek, M., Findell, K., Gentine, P., Lintner, B., Scott, R.L., Van Den Hurk, B., Seneviratne, S. 2014. Land surface controls on afternoon precipitation diagnosed from observational data: Uncertainties and confounding factors. Atmospheric Chemistry and Physics. 14:8343-8367. https://doi.org/10.5194/acp-14-8343-2014.
Interpretive Summary: Precipitation falls from the atmosphere and replenishes moisture in the soil. This moisture in turn can evaporate and return to the atmosphere, possibly leading to more precipitation. This link has long been a topic of research because of its potential to improve weather forecasting. This study investigated the poorly understood link between surface evaporation and subsequent precipitation by investigating the impact of before-noon evaporation strength on the frequency of afternoon precipitation over the contiguous US. We analyzed satellite and radar data products, met station data, and computer model output. While most computer model datasets agree there is a positive relationship between evaporation strength and precipitation in the eastern and southwestern US, observation-based estimates also indicated a strong relationship in the Central US which was not found in computer model analysis. Further analysis reveals that precipitation events tended to be clustered in space and time and this leads to a relationship which may not be casual. This study’s findings uncover a large range of unresolved issues for this topic. More investigations are needed to better pin down this complicated relationship.
Technical Abstract: The feedback between soil moisture and precipitation has long been a topic of interest due to its potential for improving weather and seasonal forecasts. The generally proposed mechanism assumes a control of soil moisture on precipitation via the partitioning of the surface fluxes (the Evaporative Fraction, EF, i.e. the ratio of latent heat to the sum of latent and sensible heat), in particular under convective conditions. Our study investigates the poorly understood link between EF and precipitation by investigating the impact of before-noon EF on the frequency of afternoon precipitation over the contiguous US. We analyze remote sensing data products (EF from GLEAM, radar precipitation from NEXRAD), FLUXNET station data, and the North American Regional Reanalysis (NARR). While most datasets agree on the existence of regions of positive relationship between EF and precipitation in the Eastern and Southwestern US, observation-based estimates also indicate a strong relationship in the Central US which is not found in NARR. Investigating these differences, we find that much of these relationships can be explained by precipitation persistence alone, with ambiguous results on the additional role of EF. Regional analyses reveal contrasting mechanisms over different regions. Over the Eastern US, our analyses suggest that the apparent EF-precipitation coupling takes place on a short day-to-day time scale and is either atmospherically controlled (from precipitation persistence and potential evaporation) or driven by vegetation interception (rather than soil moisture), in line with the high forest cover and the wet regime of that region. Over the Central and Southwestern US, the impact of EF on convection triggering is additionally linked to soil moisture variations, owing to the soil moisture–limited climate regime.