Weidong Guo

Sensitivity of a regional climate model to land surface parameterization schemes for East Asian summer monsoon simulation

Land surface processes play an important role in the East Asian Summer Monsoon (EASM) system. Parameterization schemes of land surface processes may cause uncertainties in regional climate model (RCM) studies for the EASM. In this paper, we investigate the sensitivity of a RCM to land surface parameterization (LSP) schemes for long-term simulation of the EASM. The Weather Research and Forecasting (WRF) Model coupled with four different LSP schemes (Noah-MP, CLM4, Pleim–Xiu and SSiB), hereafter referred to as Sim-Noah, Sim-CLM, Sim-PX and Sim-SSiB respectively, have been applied for 22-summer EASM simulations. The 22-summer averaged spatial distributions and strengths of downscaled large-scale circulation, 2-m temperature and precipitation are comprehensively compared with ERA-Interim reanalysis and dense station observations in China. Results show that the downscaling ability of RCM for the EASM is sensitive to LSP schemes. Furthermore, this study confirms that RCM does add more information to the EASM compared to reanalysis that imposes the lateral boundary conditions (LBC) because it provides 2-m temperature and precipitation that are with higher resolution and more realistic compared to LBC. For 2-m temperature and monsoon precipitation, Sim-PX and Sim-SSiB simulations are more consistent with observation than simulations of Sim-Noah and Sim-CLM. To further explore the physical and dynamic mechanisms behind the RCM sensitivity to LSP schemes, differences in the surface energy budget between simulations of Ens-Noah-CLM (ensemble mean averaging Sim-Noah and Sim-CLM) and Ens-PX-SSiB (ensemble mean averaging Sim-PX and Sim-SSiB) are investigated and their subsequent impacts on the atmospheric circulation are analyzed. It is found that the intensity of simulated sensible heat flux over Asian continent in Ens-Noah-CLM is stronger than that in Ens-PX-SSiB, which induces a higher tropospheric temperature in Ens-Noah-CLM than in Ens-PX-SSiB over land. The adaptive modulation of geopotential height gradients affects wind field (through geostrophic balance) simulation especially at lower levels, which subsequently affects the simulation of large-scale circulation, 2-m temperature and monsoon precipitation as well as RCM’s downscaling ability.

Influence of the Madden-Julian oscillation on Tibetan Plateau snow cover at the intraseasonal time-scale.

The Tibetan Plateau (TP), known as the third pole of the Earth, has snow cover with intraseasonal to decadal variability that affects weather and climate both inside and outside the TP. However, the factors that generate the TP snow cover (TPSC) anomalies at the intraseasonal time-scale are unclear. This report reveals the influence of the Madden‒Julian oscillation (MJO), which is the most dominant component of the tropical intraseasonal variability, on TPSC. We focus on wintertime snow cover over the central and eastern TP, where the intraseasonal variability is large. TPSC increases/decreases in the MJO phases 8‒1/4–5, when the eastward-propagating MJO suppressed/enhanced convection locates over the Maritime Continent. Such a change in TPSC leads to the most dominant positive/negative anomalies of TPSC in the following phases 2‒3/6‒7 due to the non-significant change of TPSC in these phases. There is anomalous moisture advection over the upstream of the TP caused by MJO-excited large-scale atmospheric circulation. The advection process generates the low-frequency eastward-propagating anomalous water vapour from upstream to the TP that influences precipitation and, eventually, TPSC.

Composite analysis of impacts of dust aerosols on surface atmospheric variables and energy budgets in a semiarid region of China

Loess Plateau is one of the dust aerosol source regions featured by its sandy underlying surface and affected significantly by dust events. In order to investigate climatic forcing of dust aerosols in semiarid region, continuous observations of particulate matter (PM10 concentration), meteorological elements, and energy fluxes were collected at Semiarid Climate Observatory and Laboratory in northwestern China from March to May during 2007–2010. The result shows that dusty days are often evoked under the condition when a strengthening trough is combined with the development of strong convection. During dusty days, the frequency of northerly winds increases significantly with the average wind velocity to be around 4.0 m/s; temperature is low during the daytime and high at nighttime. Relative humidity and surface pressure, however, are about 15% and 70% lower than average in dusty days, respectively. Energy balance closure is typically poor in dusty days. During daytime, the downward/upward solar radiation at land surface is less in dusty days than in nondusty days with the largest difference of 206.7 W/m2 and 33.25 W/m2, respectively. Difference in downward longwave radiation between dusty and nondusty days is 35 W/m2, accounting for 11.7% and 14% of the daily mean for dusty and nondusty days, respectively. The net radiation flux, as well as sensible/latent heat fluxes at surface is smaller during the daytime but larger at nighttime in dusty days. The maximum differences of sensible/latent heat fluxes between dusty and nondusty days can reach for 41.9% and 12.1% of the maximum net radiation, respectively.

Implementation and evaluation of a generalized radiative transfer scheme within canopy in the soil‐vegetation‐atmosphere transfer (SVAT) model

PUBLICATIONS Journal of Geophysical Research: Atmospheres RESEARCH ARTICLE 10.1002/2016JD025328 Key Points: • A generalized radiative transfer scheme within canopy was implemented • Nonuniform leaf angle distribution was considered in the areas of broadleaf trees • Albedo was increased due to nonuniform leaf optical properties in the boreal winter Correspondence to: W. Guo and Y. Xue, guowd@nju.edu.cn; yxue@geog.ucla.edu Citation: Qiu, B., W. Guo, Y. Xue, and Q. Dai (2016), Implementation and evaluation of a generalized radiative transfer scheme within canopy in the soil-vegetation- atmosphere transfer (SVAT) model, J. Geophys. Res. Atmos., 121, 12,145–12,163, doi:10.1002/ 2016JD025328. Received 5 MAY 2016 Accepted 10 OCT 2016 Accepted article online 12 OCT 2016 Published online 28 OCT 2016 Implementation and evaluation of a generalized radiative transfer scheme within canopy in the soil-vegetation- atmosphere transfer (SVAT) model Bo Qiu 1,2 , Weidong Guo 1,3,4 , Yongkang Xue 2 , and Qiudan Dai 5 Institute for Climate and Global Change Research, School of Atmospheric Sciences, Nanjing University, Nanjing, China, Department of Geography and Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, California, USA, 3 Joint International Research Laboratory of Atmospheric and Earth System Sciences of Ministry of Education, Nanjing, China, 4 Collaborative Innovation Center of Climate Change, Jiangsu Province, Nanjing, China, 5 State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China Abstract The process of radiative transfer over vegetated areas has a profound impact on energy, water, and carbon balances over the terrestrial surface. In this paper, a generalized radiative transfer scheme (GRTS) within canopy is implemented in the Simplified Simple Biosphere land surface model (SSiB). The main concept and structure of GRTS and its coupling methodology to a land model are presented. Different from the two-stream method, the GRTS takes into account the effects of complex canopy morphology and inhomogeneous optical properties of leaves on radiative transfer process within the canopy. In the offline SSiB/GRTS simulation for the period of 2001–2012, the nonuniform leaf angle distribution within canopy layers is considered in SSiB/GRTS in the areas of evergreen broadleaf trees. Compared with the SSiB/two stream method, SSiB/GRTS produces lower canopy reflectance and higher transmittance, which leads to more realistic albedo simulation. The canopy-absorbed radiation flux in SSiB/GRTS simulation is lower than that in SSiB/two stream method simulation throughout the year in the areas of evergreen broadleaf trees. The largest difference of 18.4 W/m 2 occurs in the Amazon region in the autumn. The ground-absorbed radiation flux increases in the SSiB/GRTS simulation, especially in the spring and autumn. The largest difference in the ground-absorbed radiation flux between SSiB/GRTS simulation and SSiB/two stream method simulation is 25.45 W/m 2 . In the boreal winter season, compared with the two-stream method in the SSiB, the GRTS gives higher surface albedo in the areas with high snow cover fraction over leaf. 1. Introduction The process of radiative transfer within canopy, which includes the reflected and absorbed radiation by canopy and ground, has a profound impact on the distribution of the solar radiation between the surface and the atmosphere. And this issue is essential for land surface modeling [Sellers, 1985; Yuan et al., 2014]. Surface albedo, which is important for the surface energy budget and surface-atmosphere interaction, is defined as the ratio of reflected solar radiation to incident solar radiation. The sensitivity of the climate system to surface albedo has been tested in many previous studies [Charney et al., 1977; Sud and Fennessy, 1982; Xue and Shukla, 1993; Dirmeyer and Shukla, 1996], which indicates that the changes in surface albedo have an effect on surface energy and affect latent and sensible heat fluxes, eventually leading to changes in atmo- spheric circulation and precipitation. The surface albedo plays a key role in climate simulations [Wang et al., 2006; Gu et al., 2002; Li et al., 2015]. Moreover, the visible radiation absorbed by the canopy is one of the critical factors of affecting transpiration, photosynthesis, and carbon exchange between the canopy and the atmosphere. In addition, the radiation absorbed by the ground is a basic control factor in determin- ing the water and energy exchanges between the soil and snow. Therefore, the importance of canopy radia- tive transfer process has been stressed in the development of biogeophysical and biogeochemical models. ©2016. American Geophysical Union. All Rights Reserved. QIU ET AL. Surface albedos simulated by climate models have been compared with satellite-derived albedos and large differences have been found [Oleson et al., 2003]. The previous climate sensitivity studies have suggested that an albedo error larger than 0.02–0.05 can lead to significant responses in climate models [Xue et al., 2010]. The range of 0.02–0.05 is thus considered to be a constraint for the albedo accuracy requirement. Snow over the canopy makes the albedo simulation more complex. And the snow-masking effect of vegetation has been RADIATIVE TRANSFER SCHEME WITHIN CANOPY

Satellite Chlorophyll Fluorescence and Soil Moisture Observations Lead to Advances in the Predictive Understanding of Global Terrestrial Coupled Carbon‐Water Cycles

Author(s): Qiu, B; Xue, Y; Fisher, JB; Guo, W; Berry, JA; Zhang, Y | Abstract: ©2018. American Geophysical Union. All Rights Reserved. The terrestrial carbon and water cycles are coupled through a multitude of connected processes among soil, roots, leaves, and the atmosphere. The strength and sensitivity of these couplings are not yet well known at the global scale, which contributes to uncertainty in predicting the terrestrial water and carbon budgets. We now have synchronous, global-scale satellite observations of critical terrestrial carbon and water cycle components: solar-induced chlorophyll fluorescence (SIF) and soil moisture. We used these observations within the framework of a global terrestrial biosphere model (Simplified Simple Biosphere Model version 2.0, SSiB2) to investigate carbon-water coupling processes. We updated SSiB2 to include a mechanistic representation of SIF and tested the sensitivity of model parameters to improve the simulation of both SIF and soil moisture with the ultimate objective of improving the first-order terrestrial carbon component, gross primary production. Although several vegetation parameters, such as leaf area index and the green leaf fraction, improved the simulated SIF, and several soil parameters, such as hydraulic conductivity, improved simulated soil moisture, their effects were mainly limited to their respective cycles. One root-mean-square error parameter emerged as the key coupler between the carbon and water cycles: the wilting point. Updates to the wilting point significantly improved the simulations for SIF and gross primary production although substantial mismatches with the satellite data still existed. This study demonstrates the value of synchronous global measurements of the terrestrial carbon and water cycles in improving the understanding of coupled carbon-water cycles.

Modifications on the surface layer scheme in RegCM4.3.5-CLM

The surface layer scheme in the Land Surface Model (CLM3.5) is revised for the new version of Regional Climate Model (RegCM4.3.5). In the original scheme, the stable and unstable regimes are divided into four pieces and the criteria that used for divisions are arbitrary and abrupt transitions between different pieces exist. In the modification, for the unstable conditions, the similarity functions are a blend of the widely used Paulson type expressions for near-neutral stratification plus a parameterization that takes into account highly convective conditions. For the stable regime, the formulations proposed by Cheng and Brutsaert are applied, which cover a wide range of stable stratification. The revised scheme is able to apply over a wider range of atmospheric stabilities than the old one without jump in different regimes, and the restrictions artificially imposed on certain variables in the old surface layer scheme are removed or suppressed. The old and revised schemes are tested over the East Asian domain with 10-year simulations. Two schemes present quite different flux simulations. Compared with observations, simulated surface variables biases are substantially decreased using the revised scheme. Impacts of the revised scheme on the simulation of several important surface variables, heat fluxes and precipitation are analyzed.

A Variational Method for Estimating Surface Fluxes with Mass Conservation Constraint

AbstractOn the basis of the similarity theory of the atmospheric surface layer and the mass conservation principle, a new scheme using a variational method is developed to estimate the surface momentum and sensible and latent heat fluxes. In this scheme, the mass conservation is introduced into the cost function as a weak physical constraint, which leads to an overdetermined system. For the variational method with mass conservation constraint, only the conventional meteorological observational data are taken into account. Data collected in the Yellow River Source Region Climate and Environment Observation and Research Station at Maqu, China, during 11–25 August 2010 are used to test this new scheme. Results indicate that this scheme is more reliable and accurate than both the flux-profile method and the variational method without mass conservation constraint. In addition, the effect of the weights in the cost function is examined. Sensitivity tests show that the fluxes estimated by the proposed scheme are...

Influence of Tibetan Plateau snow cover on East Asian atmospheric circulation at medium-range time scales

The responses of atmospheric variability to Tibetan Plateau (TP) snow cover (TPSC) at seasonal, interannual and decadal time scales have been extensively investigated. However, the atmospheric response to faster subseasonal variability of TPSC has been largely ignored. Here, we show that the subseasonal variability of TPSC, as revealed by daily data, is closely related to the subsequent East Asian atmospheric circulation at medium-range time scales (approximately 3–8 days later) during wintertime. TPSC acts as an elevated cooling source in the middle troposphere during wintertime and rapidly modulates the land surface thermal conditions over the TP. When TPSC is high, the upper-level geopotential height is lower, and the East Asia upper-level westerly jet stream is stronger. This finding improves our understanding of the influence of TPSC at multiple time scales. Furthermore, our work highlights the need to understand how atmospheric variability is rapidly modulated by fast snow cover changes.The atmospheric response to subseasonal variability of Tibetan Plateau snow cover has been largely ignored. Here the authors show that the fast subseasonal variability of Tibetan Plateau snow cover is closely related to the subsequent East Asian atmospheric circulation at medium-range time scales.

Spring Land Surface and Subsurface Temperature Anomalies and Subsequent Downstream Late Spring‐Summer Droughts/Floods in North America and East Asia

Author(s): Xue, Y; Diallo, I; Li, W; David Neelin, J; Chu, PC; Vasic, R; Guo, W; Li, Q; Robinson, DA; Zhu, Y; Fu, C; Oaida, CM | Abstract: ©2018. American Geophysical Union. All Rights Reserved. Sea surface temperature (SST) variability has been shown to have predictive value for land precipitation, although SSTs are unable to fully predict intraseasonal to interannual hydrologic extremes. The possible remote effects of large-scale land surface temperature (LST) and subsurface temperature (SUBT) anomalies in geographical areas upstream and closer to the areas of drought/flood have largely been ignored. Here evidence from climate observations and model simulations addresses these effects. Evaluation of observational data using Maximum Covariance Analysis identifies significant correlations between springtime 2-m air temperature (T2 m) cold (warm) anomalies in both the western U.S. and the Tibetan Plateau and downstream drought (flood) events in late spring/summer. To support these observational findings, climate models are used in sensitivity studies, in which initial LST/SUBT anomaly is imposed to produce observed T2 m anomaly, to demonstrate a causal relationship for two important cases: between spring warm T2 m/LST/SUBT anomalies in western U.S. and the extraordinary 2015 flood in Southern Great Plains and adjacent regions and between spring cold T2 m/LST/SUBT anomalies in the Tibetan Plateau and the severe 2003 drought south of the Yangtze River region. The LST/SUBT downstream effects in North America are associated with a large-scale atmospheric stationary wave extending eastward from the LST/SUBT anomaly region. The effects of SST in these cases are also tested and compared with the LST/SUBT effects. These results suggest that consideration of LST/SUBT anomalies has the potential to add value to intraseasonal prediction of dry and wet conditions, especially extreme drought/flood events. The results suggest the importance of developing land data and models capable of preserving observed soil memory.