scholarly journals Atmospheric rivers in the Australia-Asian region: a BoM–CMA collaborative study

2020 ◽  
Author(s):  
Chengzhi Ye ◽  
Huqiang Zhang ◽  
Aurel Moise ◽  
Ruping Mo
Keyword(s):  
Water Vapour ◽  
Moisture Transport ◽  
Weather Prediction ◽  
Boreal Summer ◽  
Atmospheric Moisture ◽  
Atmospheric Rivers ◽  
Extreme Precipitation Events ◽  
Set Up ◽  
Atmospheric Moisture Transport

The name ‘atmospheric river’ (AR) could easily be misinterpreted to mean rivers flowing in the sky. But, ARs actually refer to narrow bands of strong horizontal water vapour transport that are concentrated in the lower troposphere. These bands are called ‘atmospheric rivers’ because the water vapour flux they carry is close to the volume of water carried by big river systems on the ground. ARs can cause heavy rainfall events if some physical mechanisms, such as orographic enhancement, exist to set up the moisture convergence and vertical motions necessary to produce condensation. In recent decades, these significant moisture plumes have attracted increasing attention from scientific communities, especially in North America and western Europe, to further understand the connections between ARs and extreme precipitation events which can trigger severe natural disasters such as floods, mudslides and avalanches. Yet very limited research has been conducted in the Australia-Asian (A-A) region, where the important role of atmospheric moisture transport has long been recognised for its rainfall generation and variations. In this paper, we introduce a collaborative project between the Australian Bureau of Meteorology and China Meteorological Administration, which was set up to explore the detailed AR characteristics of atmospheric moisture transport embedded in the A-A monsoon system. The project in China focused on using AR analysis to explore connections between moisture transport and extreme rainfall mainly during the boreal summer monsoon season. In Australia, AR analysis was used to understand the connections between the river-like Northwest Cloud Band and rainfall in the region. Results from this project demonstrate the potential benefits of applying AR analysis to better understand the role of tropical moisture transport in rainfall generation in the extratropics, thus achieve better rainfall forecast skills at NWP (Numerical Weather Prediction), sub-seasonal and seasonal time scales. We also discuss future directions of this collaborative research, including further assessing potential changes in ARs under global warming.

scholarly journals Relative Contributions of Synoptic and Low-Frequency Eddies to Time-Mean Atmospheric Moisture Transport, Including the Role of Atmospheric Rivers

2012 ◽  
Vol 25 (21) ◽  
pp. 7341-7361 ◽  
Author(s):  
Matthew Newman ◽  
George N. Kiladis ◽  
Klaus M. Weickmann ◽  
F. Martin Ralph ◽  
Prashant D. Sardeshmukh
Keyword(s):  
Moisture Transport ◽  
Low Frequency ◽  
The Arctic ◽  
Moisture Budget ◽  
Atmospheric Moisture ◽  
Atmospheric Rivers ◽  
Low Frequency Variability ◽  
The Mean ◽  
Mean Circulation ◽  
Atmospheric Moisture Transport

The relative contributions to mean global atmospheric moisture transport by both the time-mean circulation and by synoptic and low-frequency (periods greater than 10 days) anomalies are evaluated from the vertically integrated atmospheric moisture budget based on 40 yr of “chi corrected” NCEP–NCAR reanalysis data. In the extratropics, while the time-mean circulation primarily moves moisture zonally within ocean basins, low-frequency and synoptic anomalies drive much of the mean moisture transport both from ocean to land and toward the poles. In particular, during the cool-season low-frequency variability is the largest contributor to mean moisture transport into southwestern North America, Europe, and Australia. While some low-frequency transport originates in low latitudes, much is of extratropical origin due to large-scale atmospheric anomalies that extract moisture from the northeast Pacific and Atlantic Oceans. Low-frequency variability is also integral to the Arctic (latitudes > 70°N) mean moisture budget, especially during summer, when it drives mean poleward transport from relatively wet high-latitude continental regions. Synoptic variability drives about half of the mean poleward moisture transport in the midlatitudes of both hemispheres, consistent with simple “lateral mixing” arguments. Extratropical atmospheric transport is also particularly focused within “atmospheric rivers” (ARs), relatively narrow poleward-moving moisture plumes associated with frontal dynamics. AR moisture transport, defined by compositing fluxes over those locations and times where column-integrated water vapor and poleward low-level wind anomalies are both positive, represents most of the total extratropical meridional moisture transport. These results suggest that understanding potential anthropogenic changes in the earth ’s hydrological cycle may require understanding corresponding changes in atmospheric variability, especially on low-frequency time scales.

scholarly journals Case studies of atmospheric rivers over China and Australia: new insight into their rainfall generation

2020 ◽  
Author(s):  
Jingjing Chen ◽  
Huqiang Zhang ◽  
Chengzhi Ye ◽  
Hongzhuan Chen ◽  
Ruping Mo
Keyword(s):  
Water Vapour ◽  
Asian Summer Monsoon ◽  
Weather Prediction ◽  
Winter Season ◽  
Extreme Rainfall ◽  
Boreal Summer ◽  
Austral Winter ◽  
Cloud Band ◽  
Atmospheric Rivers ◽  
Weather And Climate

While the Australia–Asian (A-A) monsoon is a prominent feature of weather and climate in China and Australia, there are significant differences in their dominant weather patterns and climate drivers. In order to explore different characteristics of atmospheric rivers (ARs) affecting weather and climate in these two countries, this paper compares two typical AR events that occurred in the boreal summer (austral winter) in 2016. The event in China produced record-breaking rainfall in North China, whereas the event in Australia was accompanied by a classic Northwest Cloud Band (NWCB) and produced a rainfall belt across the continent. Using global reanalysis products and ground-based observational data, we analysed the synoptic backgrounds, vertical structures, water vapour sources and relationship between ARs and cloud distributions. In both China and Australia, heavy precipitation was triggered by strong water vapour transport by ARs ahead of midlatitude frontal systems. The main differences between these two AR events and their associated rainfall effectiveness were that (i) the AR intensity in the Asian summer monsoon was stronger than that in the austral winter season over Australia; (ii) the centre of AR maximum moisture transport in China was around 850hPa, whereas in Australia, it was located at around 700hPa; and (iii) the AR-induced rainfall was heavier in China than in Australia. These differences were caused by numerous factors, including a lack of topographic influence, a dry climate background in Australia, and different interactions between warm and moist air conveyed by ARs from the tropics with cold air from the midlatitudes. We paid particular attention to the relationship between the Australian AR and its associated cloud structure and rainfall to understand precipitation efficiency of the NWCB. In addition, we assessed the forecast skills of an Australian numerical weather prediction system (ACCESS-APS2) for the two events with different lead times. The model produced reasonable forecasts of the occurrence and intensity of both AR events several days in advance, and the AR forecast skill was better than its forecasts of rainfall location and intensity. This demonstrates the value of using AR analysis in guiding extreme rainfall forecasts with longer lead time.

From Amazonia to southern Africa: atmospheric moisture transport through low-level jets and atmospheric rivers

2018 ◽  
Vol 1436 (1) ◽  
pp. 217-230 ◽  
Author(s):  
Alexandre M. Ramos ◽  
Ross C. Blamey ◽  
Iago Algarra ◽  
Raquel Nieto ◽  
Luis Gimeno ◽  
...  
Keyword(s):  
Southern Africa ◽  
Moisture Transport ◽  
Atmospheric Moisture ◽  
Atmospheric Rivers ◽  
Low Level ◽  
Low Level Jets ◽  
Atmospheric Moisture Transport

scholarly journals Drought and wet episodes in Amazonia: the role of atmospheric moisture transport

2017 ◽  
Author(s):  
Rogert Sorí ◽  
José Marengo ◽  
Raquel Nieto ◽  
Anita Drumond ◽  
Luis Gimeno
Keyword(s):  
Moisture Transport ◽  
Atmospheric Moisture ◽  
Atmospheric Moisture Transport

Atmospheric Moisture Transport Moderates Climatic Response to the Opening of Drake Passage

2009 ◽  
Vol 22 (9) ◽  
pp. 2483-2493 ◽  
Author(s):  
Willem P. Sijp ◽  
Matthew H. England
Keyword(s):  
Moisture Transport ◽  
Hydrological Cycle ◽  
Coupled Model ◽  
Drake Passage ◽  
Moisture Diffusivity ◽  
Atmospheric Moisture ◽  
Oceanic Circulation ◽  
Coupled Models ◽  
Storm Activity ◽  
Atmospheric Moisture Transport

Abstract The absence of the Drake Passage (DP) gateway in coupled models generally leads to vigorous Antarctic bottom water (AABW) formation, Antarctic warming, and the absence of North Atlantic deep-water (NADW) formation. Here the authors show that this result depends critically on atmospheric moisture transport by midlatitude storms. The authors use coupled model simulations employing geometries different only at the location of DP to show that oceanic circulation similar to that of the present day is possible when DP is closed and atmospheric moisture transport values enhanced by Southern Ocean storm activity are used. In this case, no Antarctic warming occurs in conjunction with DP closure. The authors also find that the changes in poleward heat transport in response to the establishment of the Antarctic Circumpolar Current (ACC) are small. This result arises from enhanced atmospheric moisture transport at the midlatitudes of the Southern Hemisphere (SH), although the values used remain within a range appropriate to the present day. In contrast, homogeneous or (near) symmetric moisture diffusivity leads to strong SH sinking and the absence of a stable Northern Hemisphere (NH) overturning state, a feature familiar from previous studies. The authors’ results show that the formation of NADW, or its precursor, may have been possible before the opening of the DP at the Eocene/Oligocene boundary, and that its presence depends on an interplay between the existence of the DP gap and the hydrological cycle across the midlatitude storm tracks.

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