Evaluation of WRF land surface schemes in land-atmosphere exchange simulations over grassland in Southeast Tibet Publication date: April 2020 Source: Atmospheric Research, Volume 234 Author(s): Shupo Ma, Libo Zhou, Fei Li, Jinhuan Zhu Abstract Land surface schemes (LSSs) evaluation is essentially important for land-atmosphere energy exchange simulation over the Tibetan Plateau (TP), especially over the Southeast Tibet, where the atmospheric systems of the TP and South Asia interact most. In May 20–July 9, 2013, an observation was conducted over the grassland in the Southeast Tibet, with radiation, sensible, latent and ground heat fluxes measured. Based on the observation data, all seven WRF (the Weather Research and Forecasting Model) coupled LSSs (SLAB, Noah, RUC, Noah-MP, CLM, PX, SSiB) were assessed. All the LSSs can successfully reproduce the diurnal variation of land-atmosphere heat transfer but with amplitude differences from observations. The LSSs also reproduced the variations of land-atmosphere exchange processes under different synoptic situations, especially at the South Asian summer monsoon (SASM) south and north phases. However, large magnitude differences exist within the LSSs simulations in comparison with the observations, which complicated our scheme evaluations and optimal LSSs selections for the Southeast Tibet. Further quantitative studies revealed that the WRF-Noah scheme performed the best among all seven LSSs in retrieving the land-atmosphere heat transfer, partly due to the its most successful surface temperature simulation. Our results suggest that the WRF-Noah scheme should be applied for future land-atmosphere exchange simulations over the Southeast Tibet.

Corrigendum to “Global climatology of nocturnal low-level jets and associated moisture sources and sinks” [Atmospheric Research (2019) 39–59] Publication date: April 2020 Source: Atmospheric Research, Volume 234 Author(s): Iago Algarra, Jorge Eiras-Barca, Raquel Nieto, Luis Gimeno

Investigation to the relation between meteorological drought and hydrological drought in the upper Shaying River Basin using wavelet analysis Publication date: April 2020 Source: Atmospheric Research, Volume 234 Author(s): Qiongfang Li, Pengfei He, Yongchang He, Xingye Han, Tianshan Zeng, Guobin Lu, Hongjie Wang Abstract Investigation to the relation between meteorological drought and hydrological drought is important for facilitating early warning and mitigation of hydrological drought. Therefore, the propagation from the meteorological drought to hydrological drought in the upper Shaying River Basin, China was explored. Based on the goodness-of-fit test of monthly streamflow distribution from four hydrologic stations, the Pearson correlation analysis between monthly Standardized Precipitation Index accumulated periods of 1–24 months and monthly Standardizing Streamflow Index was applied to detect the propagation time between meteorological drought and hydrological drought; the continuous wavelet transform, cross wavelet transform, wavelet coherence and wavelet cross-correlation were utilized to depict the links between meteorological drought and hydrological drought in specific time-frequency bands. The results revealed: (1) different probability distributions were suitable for the Standardizing Streamflow Index at different gauging stations; (2) the propagation time from meteorological drought to hydrological drought notably varied with seasons, the longer in spring and winter and the shorter in summer and autumn; (3) hydrological drought and meteorological drought presented the similar patterns in term of phase shift; (4) close correlation existed between hydrological drought and meteorological drought with high absolute maximum and minimum wavelet cross-correlation coefficients, and changed with periodic scales and the lag time of hydrological drought to meteorological drought.

Climatology of hail in the triple border Paraná, Santa Catarina (Brazil) and Argentina Publication date: April 2020 Source: Atmospheric Research, Volume 234 Author(s): Alexandra Beal, Ricardo Hallak, Leila D. Martins, Jorge A. Martins, Guilherme Biz, Anderson P. Rudke, Cesar R.T. Tarley Abstract Hailstorms cause great damage to plantations, kill animals and cause great damage to the population. The southern region of Brazil suffers from the damages caused by hailstorms each year, with the triple border of Paraná, Santa Catarina, and Argentina being the region with the highest incidence of this event. With averages above 2.60 days yr−1 recorded at Bernardo de Irigoyen, Argentina, Chapecó and São Miguel do Oeste stations in Santa Catarina. >70% of events are recorded in late winter and spring, with September and October being the months with the highest number of occurrences. The trend analysis of hail events for winter and spring was carried out, and it was observed that for most seasons, there were no statistically significant trends for the analyzed series, but the station Montes Caseros, in Argentina presented a positive and significant tendency. The Bernardo de Irigoyen and Curuzu Cuatia stations, also in Argentina, have shown a significant negative trend that may be the result of global warming. The synoptic analysis of three events suggests that there is a combined action of atmospheric systems, which in association with the topography of the region, promote the development of severe hailstorms. There is evidence that the combination of the atmospheric conditions, including South American Low-Level Jet (SALLJ), local thermodynamic instability, frontal systems, and strong upper-level winds, create a favorable environment for hail formation in deep convection. This combination involves the transport of heat and moisture from tropical regions, high level divergence and strong directional wind shear. Graphical abstract

Chemical characterization and source analysis of water-soluble inorganic ions in PM2.5 from a plateau city of Kunming at different seasons Publication date: April 2020 Source: Atmospheric Research, Volume 234 Author(s): Wei Guo, Zhongyi Zhang, Nengjian Zheng, Li Luo, Huayun Xiao, Hongwei Xiao Abstract Water-soluble inorganic ions (WSIIs) in PM2.5 from different cities have been studied in previous studies. However, the studies of WSIIs in plateau cities are relative deficient. Due to differences in topography, climate and emission sources, the WSIIs characteristics of plateau cities are expected to be different. Here, we determined the concentrations of WSIIs (SO42−, NO3−, NH4+, Ca2+, Mg2+, Na+, K+, F−, Cl−, NO2−) in PM2.5 from different seasons of Kunming, a typical plateau city in southwest China. The data will improve our understanding of the chemical characterization and source of PM2.5 in plateau environment. Our results showed that the secondary aerosols were the main pollutants (contributing >50% to PM2.5) in PM2.5 of Kunming, which mainly from coal combustion, agricultural activities and vehicle exhaust. Seasonally, high volatility of the NO3− and NH4+ and washout effects of rainfall in hot months (wet seasons) were favorable for the decreased of pollutants, while high emission, poor dispersion conditions and low removal rate could lead to the increased of pollutants in cold months (dry seasons). It suggested that adequate NH3 and intense solar radiation promotes the photochemical reactions of SO2, NOx and NH3 to form NH4HSO4, (NH4)2SO4 and NH4NO3. High temperature in hot months would promote the volatilization of NH4NO3 in Kunming. Graphical abstract

A study of ensemble-sensitivity-based initial condition perturbation methods for convection-permitting ensemble forecasts Publication date: April 2020 Source: Atmospheric Research, Volume 234 Author(s): Xinyan Zhang, Jinzhong Min, Tianjie Wu Abstract A sensitivity-based initial condition (IC) perturbation method for convection-permitting ensemble forecasts (CPEFs) is presented and preliminarily tested. The distribution of the perturbations is based on the sensitivity patterns from the ensemble sensitivity analysis (ESA) and the fast-growing perturbations calculated by the breeding growth mode (BGM). Two convective precipitation cases are used to quantitatively and qualitatively evaluate the impacts of the perturbation schemes on the ensemble forecast skill based on the Weather Research and Forecasting (WRF) model. To generate the sensitivity-based IC perturbations, ESA is applied to the short-term convective precipitation cases to calculate the sensitivity patterns. The analysis reveals the influential factors related to the evolution of weather situations that impact the strength of the forecast precipitation. The sensitivity patterns are introduced to the IC perturbations by a sensitivity-based BGM (SeBGM) method proposed in this research, and the response of the forecast skill to different perturbation magnitudes is examined. Ensemble forecasts with sensitivity-based IC perturbations can adapt to changes in the weather regime and provide accurate simulations of the placement and strength of convective systems, leading to improvements in the precipitation forecast skill.

Multi-sensor observations of an elevated rotor during a mountain wave event in the Eastern Pyrenees Publication date: April 2020 Source: Atmospheric Research, Volume 234 Author(s): Mireia Udina, Joan Bech, Sergi Gonzalez, Maria Rosa Soler, Alexandre Paci, Josep Ramón Miró, Laura Trapero, Jean Marie Donier, Thierry Douffet, Bernat Codina, Nicolau Pineda Abstract The 15 January 2017 a strong northerly synoptic flow lead to the generation of mountain waves and heavy snowfall over the eastern Pyrenees, particularly over the Cerdanya valley near the border between France, Spain and Andorra. Measurements from several instruments deployed during the Cerdanya-2017 field campaign and satellite imagery revealed the presence of mountain waves and the formation of an associated rotor underneath the first mountain wave crest. The evolution and location of the mountain waves were studied using high temporal resolution data from a UHF wind-profiler and a vertically pointing K-band Doppler radar, separated a few kilometres in horizontal distance. A mountain wave with a wavelength about 18 km was detected in the morning and shortened slightly in the afternoon when a transient rotor, elevated approximately 140 m above the ground, was formed, disconnected from the surface flow. A strong turbulence zone was identified at the upper edge of the mountain wave, above the rotor, a feature observed in previous studies. The mountain wave and rotor induced circulation was favoured by the valley shape and the second mountain ridge location, in addition to the weak and variable winds, established during the sunset close to the valley surface. Graphical abstract

Assessing the sensitivity of land-atmosphere coupling strength to boundary and surface layer parameters in the WRF model over Amazon Publication date: April 2020 Source: Atmospheric Research, Volume 234 Author(s): Chen Wang, Yun Qian, Qingyun Duan, Maoyi Huang, Larry K. Berg, Hyeyum H. Shin, Zhe Feng, Ben Yang, Jiping Quan, Songyou Hong, Junhua Yan Abstract Modeling tools can be used to diagnose regional land-atmosphere (L-A) coupling strength in the absence of sufficient observations, but subject to uncertainties associated with parameters in model physical parameterizations. Different sensitivity analysis (SA) approaches may lead to different conclusions about the underlying sensitivities. In this study, we quantify simulation uncertainties related to parameter perturbations, and use different approaches to conduct parameter SA on the WRF model pertaining to L-A coupling strength for simulations over the Amazon region. A total of twenty parameters from the Yonsei University (YSU) planetary boundary layer (PBL) and the revised MM5 surface layer (SL) schemes were selected in this analysis. Three different SA methods, the Morris One-at-A-Time (MOAT) method, the Multivariate Adaptive Regression Splines (MARS) method, and the Sobol’ method, were employed to analyze seven WRF-simulated variables and five L-A coupling metrics. Results show that 1) parameter perturbations cause large simulation uncertainties which are comparable to those in the observations; 2) three different SA methods give consistent L-A coupling strength outcomes; 3) six out of the twenty parameters contribute 80%–95% of the total variance in the metrics analyzed, and first-order effects dominate over interaction effects; 4) the twelve variables/metrics of interest show similar sensitivity patterns to the selected parameters, which is consistent across all the methods used. Physical mechanisms for how the sensitive parameters act in determining the L-A coupling strength and associated variables also are illustrated. Our results will help quantifying L-A coupling strength and establishing a basis for parameter calibration over the Amazon region.

Impacts of topography and land use changes on the air surface temperature and precipitation over the central Peruvian Andes Publication date: April 2020 Source: Atmospheric Research, Volume 234 Author(s): Miguel Saavedra, Clementine Junquas, Jhan-Carlo Espinoza, Yamina Silva Abstract This paper focuses on the representation of the air surface temperature and precipitation using high spatiotemporal simulations (3 km–1 h) of the WRF3.7.1 model in the central Peruvian area. It covers, from east to west, the coastal zone, the western slope of the Andes, the Andean Mantaro basin (500–5000 masl), and the Andes-Amazon transition region in the eastern Andes. The study covers the January months from 2004 to 2008. Three experiments were conducted using different topography and land use data sources: (1) a control simulation using the default WRF topography and land use datasets from the United States Geological Survey (USGS); (2) a simulation changing only the topography by using the SRTM topography dataset; and (3) a simulation changing the land use data of (2) by a new dataset adapted from Eva et al. (2004). SRTM topography performed better than the control simulation for representing the actual altitudes of 57 meteorological stations that were used for precipitation and surface air temperature data. As a result, the simulations of experiments (2) and (3) produced lower bias values than that of (1). Topography change (experiment (2)) showed improvements in temperature bias that were directly associated with linear modifications of -5.6 and -6.7 °C∙km−1 in minimum and maximum temperature, respectively. Increasing (decreasing) precipitation with topography or land use change was clearly controlled by changes in the moisture flux patterns and its convergence (divergence) in the Andes-Amazon transition. On the western slope, precipitation increase could be associated with the increase in easterly flow by the smaller altitudes of the Andes mountains in SRTM topography and by increasing evaporation with new land use. Inside the Mantaro Basin, low level moisture flux seems to control the rainfall changes. Overall, relative changes (positive or negative) in precipitation due to topography or land use change could reach values above 25%.

Stochastic projection of precipitation and wet and dry spells over Pakistan using IPCC AR5 based AOGCMs Publication date: April 2020 Source: Atmospheric Research, Volume 234 Author(s): A. Nabeel, H. Athar Abstract Stochastic projections of precipitation amount, number of wet days and precipitation per wetday from 25 IPCC AR5 based AOGCMs under RCP4.5 and RCP8.5 are carried out in all climate regimes of Pakistan. In arid climate regime, the ensemble average annual precipitation is projected to decrease by about 5.56%, 3.43%, 4.94% during 2011–2030 (T1), 2046–2065 (T2), 2080–2099 (T3), relative to baseline period (TB) respectively, under RCP4.5, whereas average annual precipitation in semi-arid (humid) climate regime, is projected to increase by about 8.40% and 8.02% (2.12% and 2.61%) during T2 and T3, relative to TB, respectively. Under RCP8.5, the average annual precipitation is projected to decrease in arid climate regime during T1 and increase in semi-arid and humid climate regimes during T2 and T3, relative to TB. There is a projected increase (decrease) in precipitation during T2 (T3) in all climate regimes, relative to T1. Under RCP4.5 (RCP8.5), precipitation on wetdays in arid climate regime is projected to be 7.84 (7.64), in semi-arid climate regime it is projected to be 10.78 (10.96) and in humid climate regime it is projected to be 13.67 (13.95) mm wetday−1, during T1. During T2, precipitation per wet day in arid climate regime is projected to be 7.86 (7.83), in semi-arid climate regime it is projected to be 11.32 (11.55), and in humid climate regime it is projected to be 14.40 (14.73) mm wetday−1 under RCP4.5 (RCP8.5). Overall, under both RCPs, the average annual precipitation and number of wetdays in Pakistan are projected to progressively decrease, whereas precipitation per wetday in Pakistan is projected to progressively increase, all relative to TB.