Contribution of soil moisture variability to summer precipitation in the Northern Hemisphere

2018

JGR Atmospheres

Self Cite

Soil freezing-thawing cycle is a hallmark feature of the land surface over cold regions. Variations in soil moisture and temperature during frozen-thawing (FT) process are important for water and energy exchange between land and atmosphere. Results of regional simulations by Community Land Model version 4.5 (CLM4.5) over the Tibetan Plateau show that error of daily soil temperature is within 3°C and error of daily soil moisture is with 0.10 mm 3 /mm 3 in FT process, averaged at 10 sites of whole Tibetan Plateau. Single-point simulations show that model biases partly attribute to uncertainties of initial condition and soil category data; excluding impacts of model setting, large biases of soil moisture still exist during soil thawing, and CLM4.5 fails to simulate the diurnal cycle of soil moisture in this period. Modifications of the FT parameterizations in CLM4.5 are proposed, which include (1) use of virtual temperature (T v ) instead of constant freezing point to determine occurring of phase change, (2) introduction of phase change efficiency (ε) to optimize variation rate of soil temperature and moisture in FT process, and (3) consideration of inferred impacts of phase change on soil heat conduction. Single-point and global simulations show that compared to original parameterizations in CLM4.5, these modifications can reproduce the features of daily and diurnal variations in soil moisture and make simulation in FT process closer to the observations.

Section: Introductionmentioning

confidence: 98%

Improved Simulation of Frozen‐Thawing Process in Land Surface Model (CLM4.5)

Yang

2018

JGR Atmospheres

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“…The ERA‐Interim data are from depths of 0–7, 7–28, 28–72 and 72–189 cm below the surface, at a resolution of 0.5° × 0.5°. Here we used the soil moisture in the top two layers (0–7 and 7–28 cm), given that the soil moisture in the subsurface layer is more active than in the deep layer (Yang et al ., ). Additionally, another monthly dataset of soil moisture, obtained from the Climate Prediction Center (CPC) of National Oceanic and Atmospheric Administration (Fan and van den Dool, ; https://www.esrl.noaa.gov/psd/data/gridded/data.cpcsoil.html), was introduced to reduce the uncertainty of the ERA‐Interim soil moisture dataset.…”

Section: Methodsmentioning

confidence: 97%

“…These results indicate that variations in snow depth and soil moisture are coherent and that the signal of decreasing Arctic sea ice can be retained in both snow depth and soil moisture conditions in subsequent seasons because of the large thermal inertia of snow and soil (Charney and Shukla, ). Snow depth, on one hand, can influence climate through albedo effect; on the other, it can impact soil moisture by initiating a delayed hydrological effect on seasonal timescales and further affecting atmospheric circulation (Cohen and Rind, ; Ogi et al ., ; Edwards et al ., ; Yang et al ., ; Halder and Dirmeyer, ). We picked two soil moisture indices (SM) for each period based on the soil moisture anomalies over the Eurasian continent.…”

Section: Possible Linkage Mechanisms and Modelling Evidencementioning

confidence: 99%

Role of autumn Arctic Sea ice in the subsequent summer precipitation variability over East Asia

Yang

Zhu

Intl Journal of Climatology

et al. 2019

This study explored the interannual relationship between autumn Arctic sea ice concentration (SIC) and the subsequent summer precipitation over East Asia (EASP). Since the late‐1990s, the declining SIC in the Kara–Laptev Seas has been significantly correlated with EASP as well as extremely positive anomalies in northern China and intensely negative anomalies in central‐eastern East Asia. However, there was a weak correlation between autumn SIC and EASP before the late‐1990s. Furthermore, the anomalous precipitation pattern in summer and its connection with autumn SIC variability can be explained by the seasonal persistence of continental processes (snow depth and soil moisture) into the spring. In particular, a decreasing SIC was connected with simultaneously positive and negative precipitation anomalies over northeastern China and the Siberian region, respectively, since the late‐1990s and tends to produce corresponding soil moisture anomalies over the Eurasian continent. Declining SIC also favours increased snow depth anomalies in winter over northeastern East Asia. These anomalous signals of surface processes can persist from winter into the subsequent spring, making the connection between the autumn SIC and EASP possible. The Community Earth System Model Large Ensemble simulations further verified these physical processes. More detailed mechanism for this relationship needs to be stressed in further work by numerical simulations. The results have important implications for extending the seasonal prediction validity of EASP. Moreover, before the late‐1990s, SIC‐related circulation anomalies shifted westward and northward as negative precipitation anomalies developed over west Siberia in autumn. As a result, anomalous dry soil conditions in Siberia persisted into the subsequent spring and then led to wetter‐than‐normal conditions through locally negative soil moisture–precipitation feedback before the late‐1990s.

“…The initial condition and boundary condition come from the European Centre for Medium‐Range Weather Forecasts Interim Re‐Analysis (ERA‐Interim) data sets (Dee et al, ) with horizontal resolution of 0.25° and time resolution of 6‐hourly. Compared with other reanalysis data sets such as the National Centers for Environmental Prediction global final analysis, ERA‐Interim data sets have better quality in soil moisture (Yang et al, ) and higher resolutions to represent some detailed initial fields. The time in this study is the local standard time (LST, 8 hr later than UTC time).…”

Section: Model and Data Descriptionsmentioning

confidence: 99%

Impacts of Diabatic Heating on the Genesis and Development of an Inner Tibetan Plateau Vortex

Zhang

2018

JGR Atmospheres

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A short-lived (less than 2 days) inner Tibetan Plateau vortex (TPV) with heavy precipitation was simulated using the Weather Research and Forecasting model, and the sensitivity experiments with and without surface diabatic heating and atmospheric latent heating released by precipitation were conducted to investigate the roles of surface and atmospheric diabatic heating on the genesis and development of TPV. Results show that before the genesis of the TPV, there is an anomalous increase of surface heating flux; while a disturbance of potential vorticity (PV) at 500 hPa moves over this region, the PV is enhanced and induces the generation of TPV. The precipitation in turn reduces the surface heating flux. The release of condensation latent heating by precipitation during the development of TPV does not further contribute to its reinforcement. Instead, it is more likely a result of precipitation, tending to stabilize the atmosphere and conducive to the decay of TPV. The PV diagnoses further reveal that in the early phase, the strong diabatic heating in the lower levels associated with the increasing surface heating flux has a significantly positive contribution to the generation of the TPV. The precipitation results in the decrease of positive diabatic heating contribution at low levels. Inversely, the diabatic heating in the middle levels associated with the released latent heating of precipitation condensation tends to have the negative contribution to TPV, resulting in the decay of TPV. The study of this case can deepen our understanding on the mechanism of TPV and its precipitation.