Journal of Geophysical Research: Atmospheres

doi: 10.1002/jgrd.54741pmid: N/A

No abstract is available for this article.

Chen, Haishan; Zhan, Wanxin; Zhou, Botao; Teng, Fanda; Zhang, Jie; Zhou, Yang

doi: 10.1029/2018JD030165pmid: N/A

As one of the typical midlatitude synoptic‐scale disturbances, extratropical cyclones (ECs) can exert significant impacts on the atmospheric general circulation through its interaction with the time mean flow. Under the background of global warming, the Eurasian continent exhibits evident nonuniform warming, which has the potential to alter the atmospheric baroclinicity by changing the meridional temperature gradient and further affect the ECs activity. In this study, we investigated the possible connection between the land surface thermal anomaly over Eurasia and the summer ECs activity over East Asia together with relevant mechanisms. We found that the land surface warming (cooling) near 50°N of East Asia is associated with anomalous weak (strong) summer ECs activity over East Asia. Warm (cool) land surface usually reduces (increases) the meridional temperature gradient and further the atmospheric baroclinicity in the key area of cyclone activity, resulting in low (high) frequency of the extratropical cyclogenesis and weakened (intensified) ECs activity. The land surface warming (cooling) can also depress (benefit) the associated baroclinic conversion between the time mean effective potential energy and eddy effective potential energy, resulting in decrease (increase) in the eddy kinetic energy. As a result, the energy obtained by the synoptic‐scale eddy from the time mean flow has been reduced (increased), which favors (hampers) the extratropical cyclogenesis, causing weak (strong) cyclone activity in the middle latitude of East Asia.

Qian, QiFeng; Jia, XiaoJing; Wu, Renguang

doi: 10.1029/2019JD030245pmid: N/A

This study investigates the changes in the impact of the interannual variation of autumn snow cover over the eastern Tibetan Plateau (TP; ASCETP) on winter surface air temperature (SAT) over North America (NA) in the mid‐1990s using both observational data and a linear baroclinic numerical model. The index of ASCETP shows an abrupt change with a predominant negative phase before and a predominant positive phase after 1994; thus, the analysis is performed for two subperiods: 1979–1994 (P1) and 1995–2014 (P2). An ASCETP‐related energy budget analysis shows that the ASCETP variation has a more pronounced cooling effect on the above atmosphere in P1 than in P2. The snow‐related anomalous negative geopotential height above the TP is more pronounced and extends farther northeastward in P1 than in P2. Further analysis shows that the relationship between the ASCETP and NA winter SAT is not steady. During P1, associated with an anomalous positive ASCETP, negative geopotential height anomalies emerge over the northeastern TP. These negative anomalies impose an anomalous vorticity perturbation near the East Asian westerly jet core that propagates eastward, forming a wave train‐like pattern. It crosses the North Pacific Ocean and reaches the NA region, leading to positive and negative winter SAT anomalies over western and eastern NA, respectively. In contrast, during P2, the impact of anomalous ASCETP on the variation in the winter SAT over NA is weak, probably due to the relatively weak local cooling effect of the ASCETP and the weak ASCETP‐related vorticity forcing around the East Asian westerly jet.

Zhou, Yaping; Nelson, Kevin; Mohr, Karen I.; Huffman, George J.; Levy, Robert; Grecu, Mircea

doi: 10.1029/2019JD030449pmid: N/A

Extreme precipitation events (EPEs) have the potential to create catastrophic flooding, landslides, and infrastructure damage. We diagnose the spatial and temporal characteristics of EPEs by using the Integrated Multi‐SatellitE Retrievals for Global Precipitation Measurement mission (GPM; IMERG) precipitation estimates to construct spatial‐temporal (xy‐t) EPEs that depict both the spatial extent and temporal evolution of precipitation systems. EPEs were constructed using a recursive‐fractal approach to classify the precipitating grids across space and time as belonging to the same system, thus identifying events. This classification enables the accurate depiction of duration, areal coverage, total volume, and propagation of each EPE over its entire life cycle. Results from 4 years of IMERG statistics over the contiguous United States show that the most frequent EPEs have duration between 3 and 6 hr, an affected area of 103–5 × 104 km2, and a total precipitation volume of 106–108 m3. Spatially, EPEs occur most frequently in the northwest and northeast in the winter and spring and the southwest and southeast in summer. Fall has the least number of EPEs, and summer exhibits some of the heaviest and largest precipitation events. The diurnal cycle in frequency and precipitation volume is most prominent in summer, weaker in spring and fall, and is not discernible in winter, especially for events lasting fewer than 6 hr. The event propagation speeds indicate the influence of large‐scale circulations as winter events tend to move faster than those in the other seasons.

Taylor, Michael J.; Pautet, Pierre‐Dominique; Fritts, David C.; Kaifler, Bernd; Smith, Steven M.; Zhao, Yucheng; Criddle, Neal R.; McLaughlin, Pattilyn; Pendleton, William R.; McCarthy, Michael P.; Hernandez, Gonzalo; Eckermann, Stephen D.; Doyle, James; Rapp, Markus;

Adhikari, Abishek; Liu, Chuntao

doi: 10.1029/2019JD030788pmid: N/A

Four years (April 2014 to March 2018) of Global Precipitation Measurement (GPM) Precipitation Features data along with colocated the Modern Era Retrospective‐Analysis for Research and Applications‐2 model data are used to identify Freezing Rain Features (FRFs). A Precipitation Feature with presence of both melting layer (maximum temperature of the vertical column > 4 °C) and a layer of subfreezing air (2‐m temperature < 0 °C) adjacent to the surface is considered an FRF. During 4 years of observations, GPM and Modern Era Retrospective‐Analysis for Research and Applications‐2 identify approximately 3,096 FRFs globally (65°S–65°N). Most of them are observed over Northern Hemispheric land in the winter season. The majority of FRFs originates through the “melting process,” whereas only 35 features are associated with “warm rain” process. The locations and seasonal and diurnal distribution patterns of the FRFs over the United States are well matched with the ground‐based observations. The ground‐based observations verify approximately 70% of the FRFs over the United States. Ku‐band radar properties show that FRFs are found shallower (2–5 km) and less intense (<27 dBZ) than precipitation features in general but deeper and more intense than Snow Features. Passive microwave properties show that FRFs Tbs and Polarization‐Corrected Temperature are warmer than Snow Features at all GPM Microwave Imager channels with the largest differences in 166 GHz. The enhancement in Tbs are more distinct with warm rain FRFs. FRF Tb tends to decrease as echo top height increases at all GPM Microwave Imager channels except for 183 GHz, where Tbs have lack of dependence on echo top height.

Li, Yuanlong; Lin, Yanluan; Wang, Yuqing

doi: 10.1029/2019JD030600pmid: N/A

A 14‐hr long‐lasting spiral rainband of landfalling Typhoon Longwang (2005) was investigated based on a high‐resolution simulation using the Advanced Research version of the Weather Research and Forecasting model. This rainband was previously suggested to be triggered and maintained by vortex‐Rossby wave (VRW) dynamics based on available observations. The simulation results in the present study further suggest that the rainband originated from a previously existing wavenumber‐2 VRW. The wave amplified via a positive feedback between Ekman pumping and diabatic heating. The wavenumber‐1 convective forcing induced by the deep‐layer environmental vertical wind shear also contributed to the amplification of the rainband after its formation. Although both observations and simulation showed the long‐lived (greater than 10 hr) rainband with leading stratiform precipitation, unlike in observations, the rainband in the simulation showed a transition from an inner rainband to an outer rainband when the simulated rainband moved beyond the VRW stagnation radius at about 140 km from the storm center. As a result, in the band's later stages, VRW dynamics could not contribute to the maintenance of the rainband. Instead, both cold‐pool dynamics and vertical wind shear‐induced wavenumber‐1 convective forcing played key roles in the further maintenance of the rainband.

Innocenti, S.; Mailhot, A.; Leduc, M.; Cannon, A. J.; Frigon, A.

doi: 10.1029/2019JD031210pmid: N/A

Global warming is expected to produce modifications in the intensity, as well as in the seasonality and spatiotemporal structure of extreme precipitation. In the present study, the temporal evolution of simulated daily and subdaily precipitation extremes was analyzed to assess how they respond to climate warming over different time horizons. Pooling series from the recent 50‐member Canadian Regional Climate Model v5 Large Ensemble, the probability distributions, date and time of occurrences, and spatiotemporal structure of simulated Annual Maxima (AM) precipitation were analyzed at various spatial scales and for durations between 1 hr and 3 days. In agreement with previous studies, the results underline the large increases in AM precipitation quantiles, especially for the shortest durations and for the more extreme events (i.e., longest return periods), and modifications in their spatiotemporal scaling properties and annual and diurnal cycles. For instance, subdaily AM extremes are expected to occur later in the evening, while, no matter the duration, the extremes are expected to occur over a wider period of the year in future climate. Finally, the analysis of projected AM probability distributions showed that heavy‐tail Generalized Extreme Value (GEV) distributions will most likely be observed in the future climate, with some model grid boxes experiencing a significant increase of GEV shape parameters. These results may have major consequences in terms of the occurrence and possible impacts of the most extreme precipitation events.

Guo, Jianping; Xu, Hui; Liu, Lin; Chen, Dandan; Peng, Yiran; Yim, Steve Hung‐Lam; Yang, Yuanjian; Li, Jian; Zhao, Chun; Zhai, Panmao

doi: 10.1029/2019JD030654pmid: N/A

The long‐term trend in dust loading over East Asia remains under debate and is dependent on the study period chosen. In this study, the long‐term trends in springtime dust over East Asia and the North Pacific Ocean (NPO) during 1980–2017 were examined based on the Modern‐Era Retrospective Analysis for Research and Applications version 2 reanalysis. Results showed that there was a spatial gradient in dust aerosol loadings, with decreases from western China eastward toward the NPO. This pattern was corroborated by Cloud‐Aerosol Lidar with Orthogonal Polarization observations. Furthermore, the empirical orthogonal function method was used to reveal the leading modes of springtime dust aerosol optical depth (AOD) over East Asia and the NPO. An abrupt shift occurred in the dust AOD trend in 2010 for the empirical orthogonal function 1 mode. The dust AOD increased at a rate of approximately 2 × 10‐4/year during 1999–2009 and then decreased more sharply (around 5 × 10‐4/year) afterward. This trend reversal of dust AOD was closely associated with a decrease in 10‐m wind velocity, which induces reduced dust emission. Compared with 10‐m wind, the soil moisture is less correlated with the trend reversal in dust AOD. Additionally, the trends of dry (wet) deposition were closely associated with the trends of the dust AOD, especially for the period 2010–2016. Overall, our findings add new insights to the long‐term nonlinear variability of dust.

Yadav, S.; Venezia, R. E.; Paerl, R. W.; Petters, M. D.

doi: 10.1029/2019JD030702pmid: N/A

The sources and concentrations of ice‐nucleating particles (INPs) over India are not well known. Here, INP concentrations in rainwater from Northern India and a dust sample from the Thar Desert are characterized. Rainwater INP concentrations ranged between 104 and 3 × 107 L−1 water, spanning temperatures between −4 and −28 °C. During the monsoon season, INP concentrations were low and approached those in remote marine air mass. During the winter season, INPs active between −4 to −10 °C were occasionally observed. An increase in INP activity sometimes occurred after the initial onset of rain. The onset freezing temperature of samples active at warmer temperatures was shifted to colder temperature after heat treatment, suggesting that the INP activity stemmed from biological influence. Plating was used to isolate and sequence INP active bacterial strains from some of the rainwater samples, specifically strains of close taxonomic affiliation with the ice nucleating genera Pantoea. The size‐resolved ice nucleation active site density for 200–600‐nm particles of Thar Desert Dust ranged between 107 and 109 m−2 at −20 °C, values similar to dusts from other regions of the world. The data reported herein may help constrain models that seek to predict the impact of INP on the properties of mixed‐phased clouds over the Indian subcontinent.