• Can the GPM IMERG Final Product Accurately Represent MCSs’ Precipitation Characteristics over the Central and Eastern United States?

      Cui, Wenjun; Dong, Xiquan; Xi, Baike; Feng, Zhe; Fan, Jiwen; Univ Arizona, Dept Hydrol & Atmospher Sci (AMER METEOROLOGICAL SOC, 2020-01-16)
      Mesoscale convective systems (MCSs) play an important role in water and energy cycles as they produce heavy rainfall and modify the radiative profile in the tropics and midlatitudes. An accurate representation of MCSs' rainfall is therefore crucial in understanding their impact on the climate system. The V06B Integrated Multisatellite Retrievals from Global Precipitation Measurement (IMERG) half-hourly precipitation final product is a useful tool to study the precipitation characteristics of MCSs because of its global coverage and fine spatiotemporal resolutions. However, errors and uncertainties in IMERG should be quantified before applying it to hydrology and climate applications. This study evaluates IMERG performance on capturing and detecting MCSs' precipitation in the central and eastern United States during a 3-yr study period against the radar-based Stage IV product. The tracked MCSs are divided into four seasons and are analyzed separately for both datasets. IMERG shows a wet bias in total precipitation but a dry bias in hourly mean precipitation during all seasons due to the false classification of nonprecipitating pixels as precipitating. These false alarm events are possibly caused by evaporation under the cloud base or the misrepresentation of MCS cold anvil regions as precipitating clouds by the algorithm. IMERG agrees reasonably well with Stage IV in terms of the seasonal spatial distribution and diurnal cycle of MCSs precipitation. A relative humidity (RH)-based correction has been applied to the IMERG precipitation product, which helps reduce the number of false alarm pixels and improves the overall performance of IMERG with respect to Stage IV.
    • Characteristics of Ice Cloud–Precipitation of Warm Season Mesoscale Convective Systems over the Great Plains

      Tian, Jingjing; Dong, Xiquan; Xi, Baike; Feng, Zhe; Univ Arizona, Dept Hydrol & Atmospher Sci (AMER METEOROLOGICAL SOC, 2020-02-21)
      In this study, the mesoscale convective systems (MCSs) are tracked using high-resolution radar and satellite observations over the U.S. Great Plains during April-August from 2010 to 2012. The spatiotemporal variability of MCS precipitation is then characterized using the Stage IV product. We found that the spatial variability and nocturnal peaks of MCS precipitation are primarily driven by the MCS occurrence rather than the precipitation intensity. The tracked MCSs are further classified into convective core (CC), stratiform rain (SR), and anvil clouds regions. The spatial variability and diurnal cycle of precipitation in the SR regions of MCSs are not as significant as those of MCS precipitation. In the SR regions, the high-resolution, long-term ice cloud microphysical properties [ice water content (IWC) and ice water paths (IWPs)] are provided. The IWCs generally decrease with height. Spatially, the IWC, IWP, and precipitation are all higher over the southern Great Plains than over the northern Great Plains. Seasonally, those ice and precipitation properties are all higher in summer than in spring. Comparing the peak timings of MCS precipitation and IWPs from the diurnal cycles and their composite evolutions, it is found that when using the peak timing of IWPSR as a reference, the heaviest precipitation in the MCS convective core occurs earlier, while the strongest SR precipitation occurs later. The shift of peak timings could be explained by the stratiform precipitation formation process. The IWP and precipitation relationships are different at MCS genesis, mature, and decay stages. The relationships and the transition processes from ice particles to precipitation also depend on the low-level humidity.
    • A clear-sky radiation closure study using a one-dimensional radiative transfer model and collocated satellite-surface-reanalysis data sets

      Dolinar, Erica K.; Dong, Xiquan; Xi, Baike; Jiang, Jonathan H.; Loeb, Norman G.; Univ Arizona, Dept Hydrol & Atmospher Sci; Department of Atmospheric Sciences; University of North Dakota; Grand Forks North Dakota USA; Department of Hydrology and Atmospheric Sciences; University of Arizona; Tucson Arizona USA; Department of Atmospheric Sciences; University of North Dakota; Grand Forks North Dakota USA; Jet Propulsion Laboratory; Pasadena California USA; et al. (AMER GEOPHYSICAL UNION, 2016-11-27)
      Earth's climate is largely determined by the planet's energy budget, i.e., the balance of incoming and outgoing radiation at the surface and top of atmosphere (TOA). Studies have shown that computing clear-sky radiative fluxes are strongly dependent on atmospheric state variables, such as temperature and water vapor profiles, while the all-sky fluxes are greatly influenced by the presence of clouds. NASA-modeled vertical profiles of temperature and water vapor are used to derive the surface radiation budget from Clouds and Earth Radiant Energy System (CERES), which is regarded as one of the primary sources for evaluating climate change in climate models. In this study, we evaluate the Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2) reanalyzed clear-sky temperature and water vapor profiles with newly generated atmospheric profiles from Department of Energy Atmospheric Radiation Measurement (ARM)-merged soundings and Aura Microwave Limb Sounder retrievals at three ARM sites. The temperature profiles are well replicated in MERRA-2 at all three sites, whereas tropospheric water vapor is slightly dry below similar to 700 hPa. These profiles are then used to calculate clear-sky surface and TOA radiative fluxes from the Langley-modified Fu-Liou radiative transfer model (RTM). In order to achieve radiative closure at both the surface and TOA, the ARM-measured surface albedos and aerosol optical depths are adjusted to account for surface inhomogeneity. In general, most of the averaged RTM-calculated surface downward and TOA upward shortwave and longwave fluxes agree within similar to 5 W/m(2) of the observations, which is within the uncertainties of the ARM and CERES measurements. Yet still, further efforts are required to reduce the bias in calculated fluxes in coastal regions.
    • Cloud and Precipitation Properties of MCSs Along the Meiyu Frontal Zone in Central and Southern China and Their Associated Large‐Scale Environments

      Cui, Wenjun; Dong, Xiquan; Xi, Baike; Liu, Min; Univ Arizona, Dept Hydrol & Atmospher Sci (AMER GEOPHYSICAL UNION, 2020-03-10)
      This study focuses on investigating the cloud and precipitation features of Meiyu mesoscale convective systems (MCSs) and their relation to the large-scale environments in central and southern China using satellite observations and reanalysis data during the period 2014-2018. MCSs from two different locations, the Yangtze River Basin (YRB) and Southern China (SC), are examined separately. The Meiyu MCSs have a mean precipitation rate of 3.6 mm/hr and contribute 20% to 60% of the total precipitation during the Meiyu period. The diurnal cycle of Meiyu MCSs shows a maximum precipitation amount in the morning, which is associated with the enhanced nocturnal low-level jet (LLJ) overnight. Although the synoptic setups in YRB and SC are found to be similar when normalized around the MCS initiation locations, MCSs exhibit some differences in terms of the cloud top height, precipitation rate, and duration, which are likely by the differences in the local forcing. Large interannual variations are found in MCSs' number, cloud size, lifetime, and rainfall intensity, which is found to be associated with the interannual variabilities in the large-scale environments. By comparing the large-scale environments with climatological mean states, we find that the year with the most intense MCS activity during the study period is characterized by an intensified southwesterly LLJ, which increases the moisture transport from the Indian Ocean and an enhancement of the midtropospheric westerly jet, which induces adiabatic ascent along the Meiyu front, creating more favorable conditions for convection.
    • Comparative Study of Cloud Liquid Water and Rain Liquid Water Obtained From Microwave Radiometer and Micro Rain Radar Observations Over Central China During the Monsoon

      Zhang, Wengang; Xu, Guirong; Xi, Baike; Ren, Jing; Wan, Xia; Zhou, Lingli; Cui, Chunguang; Wu, Dongqiao; Univ Arizona, Dept Hydrol & Atmospher Sci (AMER GEOPHYSICAL UNION, 2020-10-08)
      We investigated the cloud liquid water (CLW) and rain liquid water (RLW) during weak precipitations (rain rate below 12 mm/h) using microwave radiometer and microrain radar measurements collected by the Integrative Monsoon Frontal Rainfall Experiment over central China in 2018. The CLW path increased sharply from 0.6 to 4.1 mm for precipitation clouds. RLW path presented a similar trend, although it had a larger correlation coefficient with rain rate. Precipitation efficiency reached up to similar to 50% and then clearly decreased as precipitation weakened. Because weak precipitation is mostly formed in stable nimbostratus, CLW content (CLWC) during precipitation tends to has a quasi-normal distribution with mode at 0.38 g/m(3), whereas RLW content (RLWC) shows a positively skewed distribution with mode at 0.06 g/m(3). Normalized CLWC initially increases then decreases with height in nonprecipitation clouds but varies slightly in precipitation clouds due to relatively monodispersed droplets in the weaker convective motion. CLWC derived from millimeter-wave cloud radar (MMCR) shows similar vertical distribution but with larger values. The mean normalized CLWCs are 0.06 and 0.38 g/m(3) for nonprecipitation and precipitation clouds, respectively. RLWC varies slightly with height with a mean of 0.22 g/m(3) because both the collision and breakup of raindrops are weak. A case study showed different distributions and vertical structures of CLWC and RLWC in various stages of precipitation. Thicker clouds result in larger CLWC and RLWC, which will cause greater rain rate. This qualitatively explains relationships among cloud thickness, CLW, RLW, and rain rate in precipitation during the monsoon.
    • Comparison of Daytime Low-Level Cloud Properties Derived From GOES and ARM SGP Measurements

      McHardy, Theodore M.; Dong, Xiquan; Xi, Baike; Thieman, Mandana M.; Minnis, Patrick; Palikonda, Rabindra; Univ Arizona, Dept Hydrol & Atmospher Sci (AMER GEOPHYSICAL UNION, 2018-08-16)
      Large-scale satellite data are critical for both verifying and improving general circulation model parameterizations of clouds and radiation for climate prediction. For reliable application of satellite data sets in cloud processes and climate models, it is important to have a reasonable estimate of the errors in the derived cloud properties. The daytime single-layered low-level cloud properties retrieved by the Geostationary Operational Environmental Satellite system (GOES) are compared with ground-based observations and retrievals over the Department of Energy Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) Central Facility from June 1998 to December 2006. The GOES retrievals are made via the Visible-Infrared Solar-infrared Split-window Technique. They are spatially averaged within a 0.15 degrees x 0.15 degrees box centered on the ARM SGP site, and the ARM surface observations are temporally averaged +/- 15 min around the GOES scans to produce collocated pairs. Comparisons are made for monthly means, diurnal means, and one-to-one GOES and ARM collocated pairs. GOES T-eff is highly correlated with ARM T-top cloud temperature, having an R-2 value of 0.75, though GOES exhibits a cold bias. GOES-retrieved tau and liquid water path have very good agreement with ARM retrievals with R(2)s of 0.45 and 0.47, while r(e) (GOES), on average, is about 2 mu m greater than ARM r(e). An examination of solar and viewing geometry has shown that GOES-retrieved mean r(e) and tau values are impacted by solar zenith angle and especially scattering angle, which is not unexpected and needs to be accounted for by users.
    • Effects of environment forcing on marine boundary layer cloud-drizzle processes

      Wu, Peng; Dong, Xiquan; Xi, Baike; Liu, Yangang; Thieman, Mandana; Minnis, Patrick; Univ Arizona, Dept Hydrol & Atmospher Sci; Department of Hydrology and Atmospheric Sciences; University of Arizona; Tucson Arizona USA; Department of Hydrology and Atmospheric Sciences; University of Arizona; Tucson Arizona USA; Department of Atmospheric Sciences; University of North Dakota; Grand Forks North Dakota USA; et al. (AMER GEOPHYSICAL UNION, 2017-04-27)
      Determining the factors affecting drizzle formation in marine boundary layer (MBL) clouds remains a challenge for both observation and modeling communities. To investigate the roles of vertical wind shear and buoyancy (static instability) in drizzle formation, ground-based observations from the Atmospheric Radiation Measurement Program at the Azores are analyzed for two types of conditions. The type I clouds should last for at least 5h and more than 90% time must be nondrizzling and then followed by at least 2h of drizzling periods, while the type II clouds are characterized by mesoscale convection cellular structures with drizzle occur every 2 to 4h. By analyzing the boundary layer wind profiles (direction and speed), it was found that either directional or speed shear is required to promote drizzle production in the type I clouds. Observations and a recent model study both suggest that vertical wind shear helps the production of turbulent kinetic energy (TKE), stimulates turbulence within cloud layer, and enhances drizzle formation near the cloud top. The type II clouds do not require strong wind shear to produce drizzle. The small values of lower tropospheric stability (LTS) and negative Richardson number (R-i) in the type II cases suggest that boundary layer instability plays an important role in TKE production and cloud-drizzle processes. By analyzing the relationships between LTS and wind shear for all cases and all time periods, a stronger connection was found between LTS and wind directional shear than that between LTS and wind speed shear.
    • Estimation of liquid water path below the melting layer in stratiform precipitation systems using radar measurements during MC3E

      Tian, Jingjing; Dong, Xiquan; Xi, Baike; Williams, Christopher R.; Wu, Peng; Univ Arizona, Dept Hydrol & Atmospher Sci (COPERNICUS GESELLSCHAFT MBH, 2019-07-11)
      In this study, the liquid water path (LWP) below the melting layer in stratiform precipitation systems is retrieved, which is a combination of rain liquid water path (RLWP) and cloud liquid water path (CLWP). The retrieval algorithm uses measurements from the vertically pointing radars (VPRs) at 35 and 3 GHz operated by the US Department of Energy Atmospheric Radiation Measurement (ARM) and National Oceanic and Atmospheric Administration (NOAA) during the field campaign Midlatitude Continental Convective Clouds Experiment (MC3E). The measured radar reflectivity and mean Doppler velocity from both VPRs and spectrum width from the 35 GHz radar are utilized. With the aid of the cloud base detected by a ceilometer, the LWP in the liquid layer is retrieved under two different situations: (I) no cloud exists below the melting base, and (II) cloud exists below the melting base. In (I), LWP is primarily contributed from raindrops only, i.e., RLWP, which is estimated by analyzing the Doppler velocity differences between two VPRs. In (II), cloud particles and raindrops coexist below the melting base. The CLWP is estimated using a modified attenuation-based algorithm. Two stratiform precipitation cases (20 and 11 May 2011) during MC3E are illustrated for two situations, respectively. With a total of 13 h of samples during MC3E, statistical results show that the occurrence of cloud particles below the melting base is low (9 %); however, the mean CLWP value can be up to 0.56 kgm(2), which is much larger than the RLWP (0.10 kgm(2)). When only raindrops exist below the melting base, the average RLWP value is larger (0.32 kgm(2)) than the with-cloud situation. The overall mean LWP below the melting base is 0.34 kgm(2) for stratiform systems during MC3E.
    • Evaluation of Reanalyzed Precipitation Variability and Trends Using the Gridded Gauge-Based Analysis over the CONUS

      Cui, Wenjun; Dong, Xiquan; Xi, Baike; Kennedy, Aaron; Univ Arizona, Dept Hydrol & Atmospher Sci; Department of Hydrology and Atmospheric Sciences, The University of Arizona, Tucson, Arizona; Department of Hydrology and Atmospheric Sciences, The University of Arizona, Tucson, Arizona; Department of Atmospheric Sciences, University of North Dakota, Grand Forks, North Dakota; Department of Atmospheric Sciences, University of North Dakota, Grand Forks, North Dakota (AMER METEOROLOGICAL SOC, 2017-08)
      Atmospheric reanalyses have been used in many studies to investigate the variabilities and trends of precipitation because of their global coverage and long record; however, their results must be properly analyzed and their uncertainties must be understood. In this study, precipitation estimates from five global reanalyses [ERA-Interim; MERRA, version 2 (MERRA2); JRA-55; CFSR; and 20CR, version 2c (20CRv2c)] and one regional reanalysis (NARR) are compared against the CPC Unified Gauge-Based Analysis (CPCUGA) and GPCP over the contiguous United States (CONUS) during the period 1980-2013. Reanalyses capture the variability of the precipitation distribution over the CONUS as observed in CPCUGA and GPCP, but large regional and seasonal differences exist. Compared with CPCUGA, global reanalyses generally overestimate the precipitation over the western part of the country throughout the year and over the northeastern CONUS during the fall and winter seasons. These issues may be associated with the difficulties models have in accurately simulating precipitation over complex terrain and during snowfall events. Furthermore, systematic errors found in five global reanalyses suggest that their physical processes in modeling precipitation need to be improved. Even though negative biases exist in NARR, its spatial variability is similar to both CPCUGA and GPCP; this is anticipated because it assimilates observed precipitation, unlike the global reanalyses. Based on CPCUGA, there is an average decreasing trend of -1.38mm yr(-1) over the CONUS, which varies depending on the region with only the north-central to northeastern parts of the country having positive trends. Although all reanalyses exhibit similar interannual variation as observed in CPCUGA, their estimated precipitation trends, both linear and spatial trends, are distinct from CPCUGA.
    • The footprints of 16 year trends of Arctic springtime cloud and radiation properties on September sea ice retreat

      Huang, Yiyi; Dong, Xiquan; Xi, Baike; Dolinar, Erica K.; Stanfield, Ryan E.; Univ Arizona, Dept Hydrol & Atmospher Sci; Department of Hydrology & Atmospheric Sciences; University of Arizona; Tucson Arizona USA; Department of Hydrology & Atmospheric Sciences; University of Arizona; Tucson Arizona USA; Department of Atmospheric Sciences; University of North Dakota; Grand Forks North Dakota USA; Department of Atmospheric Sciences; University of North Dakota; Grand Forks North Dakota USA; et al. (AMER GEOPHYSICAL UNION, 2017-02-27)
      The most prominent September Arctic sea ice decline over the period of 2000-2015 occurs over the Siberian Sea, Laptev Sea, and Kara Sea. The satellite observed and retrieved sea ice concentration (SIC) and cloud/radiation properties over the Arctic (70 degrees-90 degrees N) have been used to investigate the impact of springtime cloud and radiation properties on September SIC variation. Positive trends of cloud fractions, cloud water paths, and surface downward longwave flux at the surface over the September sea ice retreat areas are found over the period of 1 March to 14 May, while negative trends are found over the period of 15 May to 28 June. The spatial distributions of correlations between springtime cloud/radiation properties and September SIC have been calculated, indicating that increasing cloud fractions and downward longwave flux during springtime tend to enhance sea ice melting due to strong cloud warming effect. Surface downward and upward shortwave fluxes play an important role from May to June when the onset of sea ice melting occurs. The comparison between linearly detrended and nondetrended of each parameter indicates that significant impact of cloud and radiation properties on September sea ice retreat occurs over the Chukchi/Beaufort Sea at interannual time scale, especially over the period of 31 March to 29 April, while strongest climatological trends are found over the Laptev/Siberian Sea.
    • Intercomparisons of marine boundary layer cloud properties from the ARM CAP-MBL campaign and two MODIS cloud products

      Zhang, Zhibo; Dong, Xiquan; Xi, Baike; Song, Hua; Ma, Po-Lun; Ghan, Steven J.; Platnick, Steven; Minnis, Patrick; Univ Arizona, Dept Hydrol & Atmospher Sci; Physics Department; UMBC; Baltimore Maryland USA; et al. (AMER GEOPHYSICAL UNION, 2017-02-27)
      From April 2009 to December 2010, the Department of Energy Atmospheric Radiation Measurement (ARM) program carried out an observational field campaign on Graciosa Island, targeting the marine boundary layer (MBL) clouds over the Azores region. In this paper, we present an intercomparison of the MBL cloud properties, namely, cloud liquid water path (LWP), cloud optical thickness (COT), and cloud-droplet effective radius (CER), among retrievals from the ARM mobile facility and two Moderate Resolution Imaging Spectroradiometer (MODIS) cloud products (Goddard Space Flight Center (GSFC)-MODIS and Clouds and Earth's Radiant Energy System-MODIS). A total of 63 daytime single-layer MBL cloud cases are selected for intercomparison. Comparison of collocated retrievals indicates that the two MODIS cloud products agree well on both COT and CER retrievals, with the correlation coefficient R>0.95, despite their significant difference in spatial sampling. In both MODIS products, the CER retrievals based on the 2.1 mu m band (CER2.1) are significantly larger than those based on the 3.7 mu m band (CER3.7). The GSFC-MODIS cloud product is collocated and compared with ground-based ARM observations at several temporal-spatial scales. In general, the correlation increases with more precise collocation. For the 63 selected MBL cloud cases, the GSFC-MODIS LWP and COT retrievals agree reasonably well with the ground-based observations with no apparent bias and correlation coefficient R around 0.85 and 0.70, respectively. However, GSFC-MODIS CER3.7 and CER2.1 retrievals have a lower correlation (R similar to 0.5) with the ground-based retrievals. For the 63 selected cases, they are on average larger than ground observations by about 1.5 mu m and 3.0 mu m, respectively. Taking into account that the MODIS CER retrievals are only sensitive to cloud top reduces the bias only by 0.5 mu m.
    • Investigation of aerosol-cloud interactions under different absorptive aerosol regimes using Atmospheric Radiation Measurement (ARM) southern Great Plains (SGP) ground-based measurements

      Zheng, Xiaojian; Xi, Baike; Dong, Xiquan; Logan, Timothy; Wang, Yuan; Wu, Peng; Univ Arizona, Dept Hydrol & Atmospher Sci (COPERNICUS GESELLSCHAFT MBH, 2020-03-24)
      The aerosol indirect effect on cloud microphysical and radiative properties is one of the largest uncertainties in climate simulations. In order to investigate the aerosol-cloud interactions, a total of 16 low-level stratus cloud cases under daytime coupled boundary-layer conditions are selected over the southern Great Plains (SGP) region of the United States. The physicochemical properties of aerosols and their impacts on cloud microphysical properties are examined using data collected from the Department of Energy Atmospheric Radiation Measurement (ARM) facility at the SGP site. The aerosol-cloud interaction index (ACI(r)) is used to quantify the aerosol impacts with respect to cloud-droplet effective radius. The mean value of ACI(r) calculated from all selected samples is 0.145 +/- 0.05 and ranges from 0.09 to 0.24 at a range of cloud liquid water paths (LWPs; LWP = 20-300 g m(-2)). The magnitude of ACI(r) decreases with an increasing LWP, which suggests a diminished cloud microphysical response to aerosol loading, presumably due to enhanced condensational growth processes and enlarged particle sizes. The impact of aerosols with different light-absorbing abilities on the sensitivity of cloud microphysical responses is also investigated. In the presence of weak light-absorbing aerosols, the low-level clouds feature a higher number concentration of cloud condensation nuclei (N-CCN) and smaller effective radii (r(e)), while the opposite is true for strong light-absorbing aerosols. Furthermore, the mean activation ratio of aerosols to CCN (N-CCN/N-a) for weakly (strongly) absorbing aerosols is 0.54 (0.45), owing to the aerosol microphysical effects, particularly the different aerosol compositions inferred by their absorptive properties. In terms of the sensitivity of cloud-droplet number concentration (N-d) to N-CCN, the fraction of CCN that converted to cloud droplets (N-d/N-CCN) for the weakly (strongly) absorptive regime is 0.69 (0.54). The measured ACI(r) values in the weakly absorptive regime are relatively higher, indicating that clouds have greater microphysical responses to aerosols, owing to the favorable thermodynamic condition. The reduced ACI(r) values in the strongly absorptive regime are due to the cloud-layer heating effect induced by strong light-absorbing aerosols. Consequently, we expect larger shortwave radiative cooling effects from clouds in the weakly absorptive regime than those in the strongly absorptive regime.
    • Precipitation Influence on and Response to Early and Late Arctic Sea Ice Melt Onset During Melt Season

      Marcovecchio, Alexa; Behrangi, Ali; Dong, Xiquan; Xi, Baike; Huang, Yiyi; Department of Hydrology and Atmospheric Sciences, University of Arizona (Wiley, 2021-06-02)
      The region containing portions of the East Siberian Sea and Laptev Sea (73°–84°N, 90°–155°E) is the area of focus (AOF) for this study. The impacts of precipitation, latent heat (LH) and sensible heat (SH) fluxes on sea ice melt onset in the AOF are investigated. Four early melting years (1990, 2012, 2003, and 1991) and four late melting years (1982, 1983, 1984, and 1996) are compared to better identify the different responses to melt onset timing. A consistency check is performed between multiple Arctic precipitation products (including NASA MERRA-2, ECMWF ERA-Interim [ERA-I], and ECMWF ERA5 reanalyses as well as GPCP V2.3 observations) since there is not yet a high-quality ground-truth Arctic precipitation data product. MERRA-2 has the greatest monthly average precipitation, snowfall, evaporation, and net LH flux. ERA-I suggests that liquid precipitation starts earlier in the year than MERRA-2 and ERA5, while GPCP shows different seasonal precipitation variations from the reanalyses. MERRA-2 has the clearest and most amplified seasonal trends for the parameters used in this study, so the daily time series and anomalies of MERRA-2 variables before and after the first major melt event are investigated. ERA5 is used to check these results because ERA-I and ERA5 display similar seasonal trends. According to MERRA-2, during early melt years, surface SH flux loss and precipitation are above average in the days before and after the first major melt event. During late melt years, surface SH flux loss and precipitation are below average in the month leading up to the first major melt event. © 2021 Royal Meteorological Society
    • Profiles of MBL Cloud and Drizzle Microphysical Properties Retrieved From Ground‐Based Observations and Validated by Aircraft In Situ Measurements Over the Azores

      Wu, Peng; Dong, Xiquan; Xi, Baike; Tian, Jingjing; Ward, Dale M.; Univ Arizona, Dept Hydrol & Atmospher Sci (AMER GEOPHYSICAL UNION, 2020-04-23)
      The profiles of marine boundary layer (MBL) cloud and drizzle microphysical properties are important for studying the cloud-to-rain conversion and growth processes in MBL clouds. However, it is challenging to simultaneously retrieve both cloud and drizzle microphysical properties within an MBL cloud layer using ground-based observations. In this study, methods were developed to first decompose drizzle and cloud reflectivity in MBL clouds from Atmospheric Radiation Measurement cloud radar reflectivity measurements and then simultaneously retrieve cloud and drizzle microphysical properties during the Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA) campaign. These retrieved microphysical properties, such as cloud and drizzle particle size (r(c) and r(m,d)), their number concentration (N-c and N-d) and liquid water content (LWCc and LWCd), have been validated by aircraft in situ measurements during ACE-ENA (158 hr of aircraft data). The mean surface retrieved (in situ measured) r(c), N-c, and LWCc are 10.9 mu m (11.8 mu m), 70 cm(-3) (60 cm(-3)), and 0.21 g m(-3) (0.22 g m(-3)), respectively. For drizzle microphysical properties, the retrieved (in situ measured) r(d), N-d, and LWCd are 44.9 mu m (45.1 mu m), 0.07 cm(-3) (0.08 cm(-3)), and 0.052 g m(-3) (0.066 g m(-3)), respectively. Treating the aircraft in situ measurements as truth, the estimated median retrieval errors are 15% for r(c), 35% for N-c, 30% for LWCc and r(d), and 50% for N-d and LWCd. The findings from this study will provide insightful information for improving our understanding of warm rain processes, as well as for improving model simulations. More studies are required over other climatic regions.
    • Quantifying the Uncertainties of Reanalyzed Arctic Cloud and Radiation Properties Using Satellite Surface Observations

      Huang, Yiyi; Dong, Xiquan; Xi, Baike; Dolinar, Erica K.; Stanfield, Ryan E.; Qiu, Shaoyue; Univ Arizona, Dept Hydrol & Atmospher Sci; Department of Hydrology and Atmospheric Sciences, The University of Arizona, Tucson, Arizona; Department of Hydrology and Atmospheric Sciences, The University of Arizona, Tucson, Arizona; Department of Atmospheric Sciences, University of North Dakota, Grand Forks, North Dakota; et al. (AMER METEOROLOGICAL SOC, 2017-10)
      Reanalyses have proven to be convenient tools for studying the Arctic climate system, but their uncertainties should first be identified. In this study, five reanalyses (JRA-55, 20CRv2c, CFSR, ERA-Interim, and MERRA-2) are compared with NASA CERES-MODIS (CM)-derived cloud fractions (CFs), cloud water paths (CWPs), top-of-atmosphere (TOA) and surface longwave (LW) and shortwave (SW) radiative fluxes over the Arctic (70 degrees-90 degrees N) over the period of 2000-12, and CloudSat-CALIPSO (CC)-derived CFs from 2006 to 2010. The monthly mean CFs in all reanalyses except JRA-55 are close to or slightly higher than the CC-derived CFs from May to September. However, wintertime CF cannot be confidently evaluated until instrument simulators are implemented in reanalysis products. The comparison between CM and CCCFs indicates that CM-derived CFs are reliable in summer but not in winter. Although the reanalysis CWPs follow the general seasonal variations of CM CWPs, their annual means are only half or even less than the CM-retrieved CWPs (126 g m(-2)). The annual mean differences in TOA and surface SW and LW fluxes between CERES EBAF and reanalyses are less than 6 W m(-2) for TOA radiative fluxes and 16 W m(-2) for surface radiative fluxes. All reanalyses show positive biases along the northern and eastern coasts of Greenland as a result of model elevation biases or possible CM clear-sky retrieval issues. The correlations between the reanalyses and CERES satellite retrievals indicate that all five reanalyses estimate radiative fluxes better than cloud properties, and MERRA-2 and JRA-55 exhibit comparatively higher correlations for Arctic cloud and radiation properties.
    • A Regime-Based Evaluation of Southern and Northern Great Plains Warm-Season Precipitation Events in WRF

      Wang, Jingyu; Dong, Xiquan; Kennedy, Aaron; Hagenhoff, Brooke; Xi, Baike; Univ Arizona, Dept Hydrol & Atmospher Sci (AMER METEOROLOGICAL SOC, 2019-08)
      A competitive neural network known as the self-organizing map (SOM) is used to objectively identify synoptic patterns in the North American Regional Reanalysis (NARR) for warm-season (April-September) precipitation events over the Southern and Northern Great Plains (SGP/NGP) from 2007 to 2014. Classifications for both regions demonstrate contrast in dominant synoptic patterns ranging from extratropical cyclones to subtropical ridges, all of which have preferred months of occurrence. Precipitation from deterministic Weather Research and Forecasting (WRF) Model simulations run by the National Severe Storms Laboratory (NSSL) are evaluated against National Centers for Environmental Prediction (NCEP) Stage IV observations. The SGP features larger observed precipitation amount, intensity, and coverage, as well as better model performance than the NGP. Both regions' simulated convective rain intensity and coverage have good agreement with observations, whereas the stratiform rain (SR) is more problematic with weaker intensity and larger coverage. Further evaluation based on SOM regimes shows that WRF bias varies with the type of meteorological forcing, which can be traced to differences in the diurnal cycle and properties of stratiform and convective rain. The higher performance scores are generally associated with the extratropical cyclone condition than the subtropical ridge. Of the six SOM classes over both regions, the largest precipitation oversimulation is found for SR dominated classes, whereas a nocturnal negative precipitation bias exists for classes featuring upscale growth of convection.
    • Spatial Distribution and Impacts of Aerosols on Clouds Under Meiyu Frontal Weather Background Over Central China Based on Aircraft Observations

      Yang, Junmei; Li, Junxia; Li, Peiren; Sun, Guode; Cai, Zhaoxin; Yang, Xiao; Cui, Chunguang; Dong, Xiquan; Xi, Baike; Wan, Rong; et al. (AMER GEOPHYSICAL UNION, 2020-08)
      An airborne field campaign was conducted from 10 June to 10 July 2018 in Hubei Province over central China as a part of the State Key Natural Science Foundation Project referred to as Integrative Monsoon Frontal Rainfall Experiment (IMFRE). Comprehensive observations of atmospheric aerosols and cloud characteristics in this region were collected and analyzed. In this study, data from six flights on nonprecipitating days were selected to investigate the spatial distribution of aerosols and microphysical properties of clouds. The profiles of aerosol number concentrations (N-a) were 1 order of magnitude lower than those over the North Plain of China, due to the different atmospheric backgrounds, local emission, and long-range transport. The highest N-a occurred at the altitude of the temperature inversion layer (TIL), indicating that N-a profiles were significantly affected by the TIL structure. Relative humidity (RH) had an effect on the aerosol size distribution where high RH values corresponded well with large values of particle mean diameter (MD). Compared with the vertical distributions of N-a and MD, their horizontal directions had minor changes, except for the MD at 4,000 m in one case. Of the three flights that penetrated through the stratiform clouds, the probability distribution functions of cloud droplet number concentration (N-c), effective radius (r(e)), and liquid water content (LWC), showed the same features with a single peak mode. Since the nucleation of aerosol in-cloud caused the decrease of aerosol concentration, the maximum aerosol activation ratio almost reached 74%. The average spectrum of cloud droplets showed a multimodal distribution and their microphysical properties were analyzed in this study.
    • Statistical Characteristics of Raindrop Size Distributions and Parameters in Central China During the Meiyu Seasons

      Fu, Zhikang; Dong, Xiquan; Zhou, Lingli; Cui, Wenjun; Wang, Jingyu; Wan, Rong; Leng, Liang; Xi, Baike; Univ Arizona, Dept Hydrol & Atmospher Sci (AMER GEOPHYSICAL UNION, 2020-09-17)
      The rain parameters derived from the laser OTT second-generation Particle Size Velocity (Parsivel(2)), the two-dimensional video disdrometer (2DVD), and DZZ5 tipping-bucket rain gauge (RG) during the Integrative Monsoon Frontal Rainfall Experiment (IMFRE) in summer 2018 are compared. The total rainfall amounts observed by Parsivel, 2DVD, and RG during IMFRE were 178.07, 176.76, and 182.5 mm, while their total rainy hours were 113, 113, and 90. The meanD(m)(mass-weighted mean diameter) andLWC(liquid water content) values derived from Parsivel and 2DVD were 1.03 and 1.01 mm and 0.247 and 0.223 g m(-3). The rainy samples from six Parsivel sites over the middle reaches of the Yangtze River during the 2016-2018 Meiyu seasons have been collected and analyzed. The occurrence frequencies for rain rates (RR) 10 mm hr(-1)were 83.9% and 7.4%, respectively, but they contributed 30.5% and 52.1% of the total accumulated rainfall. Compared with the results over the lower reaches of the Yangtze River, the total accumulated rainfall percentages forRR RR > 10 mm hr(-1)observed at XN site were higher and lower, respectively. The stratiform rain (SR) raindrop size increases withRRover both the middle and lower reaches, whereas theN(w)values over the middle reaches are much higher. Opposite to the SR results, the convective rain (CR) raindrops from this study are larger, while theirN(w)values are similar to one another. For gamma-type-size distribution, the mu - lambda andZ - Rrelations are strongly dependent on geographical location.
    • Thicker Clouds and Accelerated Arctic Sea Ice Decline: The Atmosphere‐Sea Ice Interactions in Spring

      Huang, Yiyi; Dong, Xiquan; Bailey, David A.; Holland, Marika M.; Xi, Baike; DuVivier, Alice K.; Kay, Jennifer E.; Landrum, Laura L.; Deng, Yi; Univ Arizona, Dept Hydrol & Atmospher Sci (AMER GEOPHYSICAL UNION, 2019-06-19)
      Observations show that increased Arctic cloud cover in the spring is linked with sea ice decline. As the atmosphere and sea ice can influence each other, which one plays the leading role in spring remains unclear. Here we demonstrate, through observational data diagnosis and numerical modeling, that there is active coupling between the atmosphere and sea ice in early spring. Sea ice melting and thus the presence of more open water lead to stronger evaporation and promote cloud formation that increases downward longwave flux, leading to even more ice melt. Spring clouds are a driving force in the disappearance of sea ice and displacing the mechanism of atmosphere-sea ice coupling from April to June. These results suggest the need to accurately model interactions of Arctic clouds and radiation in Earth System Models in order to improve projections of the future of the Arctic.
    • Understanding Ice Cloud‐Precipitation Properties of Three Modes of Mesoscale Convective Systems During PECAN

      Cui, Wenjun; Dong, Xiquan; Xi, Baike; Fan, Jiwen; Tian, Jingjing; Wang, Jingyu; McHardy, Theodore M.; Univ Arizona, Dept Hydrol & Atmospher Sci (AMER GEOPHYSICAL UNION, 2019-04-12)
      This study analyzes the precipitation and ice cloud microphysical features of three common modes of linear mesoscale convective systems during the Plains Elevated Convection at Night (PECAN) campaign. Three cases, one for each linear mesoscale convective system archetype (trailing stratiform, leading stratiform, and parallel stratiform precipitation), are selected. We focus primarily on analyzing ice cloud microphysical properties and precipitation rates (PRs) over the classified convective core (CC) and stratiform rain (SR) regions, as well as the two stratiform regions that developed behind (SR1) and ahead (SR2) of the convective line relative to the storm motion. In the three selected cases, the ice water path (IWP) and PR have strong correlations in the CC, but not in the SR. In terms of the temporal evolution of the mean IWPs and PRs, both CC and SR IWPs, as well as CC PRs, reach peaks quickly but take a longer time to dissipate than the increase period. For all the three cases, both SR1 and SR2 IWPs are 20-70% of their corresponding CC values in both the leading stratiform and parallel stratiform cases and up to 95% for the trailing stratiform case, while all of their PRs are only 7-25% of their CC values. These values suggest not only that the SR PRs may depend on IWPs but also that the microphysical properties of ice particles such as habit and size distribution may play an important role. Utilizing cloud-resolving simulations of these systems may provide better understanding of the physical meanings behind the results in the future.