Variability of subtropical upper tropospheric humidity

Ryoo, Ju‐Mee; Waugh, D. W.; Gettelman, Andrew

doi:10.5194/acp-8-2643-2008

Cited by 19 publications

(17 citation statements)

References 40 publications

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“…Upper level potential vorticity (PV) is a typical cause of upper level disturbances. The dynamics of PV and its relation to relative humidity (RH) and precipitation have been studied through National Centers for Environmental Prediction (NCEP)‐National Center for Atmospheric Research Reanalysis, rain gauge data, trajectories, and satellite observations such as Total Ozone Mapping Spectrometer and Atmospheric InfraRed Satellite data [ Wernli and Davies , ; Lackmann and Gyakum , ; Massacand et al , ; Waugh , ; Ryoo et al , , ; Martínez‐Alvarado et al , ]. Waugh [] showed that upper level PV often originates within dry and cold stratospheric air to the west of high PV intrusions by promoting downward motions and brings moist and warm tropospheric air to the east of high PV intrusions by inducing strong upward motions.…”

Section: Introductionmentioning

confidence: 99%

Classification of atmospheric river events on the U.S. West Coast using a trajectory model

et al. 2015

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We investigate transport pathways of water vapor associated with landfalling atmospheric river (AR) events that result in precipitation along the West Coast of the U.S. for winters of 1997-2010. The water vapor transport pathways are determined by computing back trajectories with a trajectory model using the Modern Era Retrospective analysis for Research and Applications reanalysis data set. The majority of AR events (86%) over the West Coast of the U.S. are grouped into three trajectory types, and two of them are closely associated with the AR events. We designate the first type as Ascending near landfall and of Tropical Origin (AT), the second type as Ascending near landfall and of Extratropical Origin (AE), and the third type as Descending or parallel near landfall and of Extratropical Origin (DE), which is accompanied but not directly associated with the AR events. The magnitude and spatial distribution of precipitation of a given AR event are found to be strongly determined by the type of trajectories. In general, AR events composed of both AT and AE trajectories have more frequent precipitation over a broad region of the western U.S. and AR events composed of both AT and DE trajectories have intense precipitation over the southwestern U.S. due to AT trajectories. AR events of AT-only trajectories have intense precipitation, especially over the northwestern U.S., but are less frequent compared to those of AT + AE trajectories. In addition, different patterns of trajectory types among AR events are closely linked to upper level potential vorticity (PV) anomalies; 66% of AR events are associated with anticyclonic Rossby wave breaking events.

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Section: Introductionmentioning

confidence: 99%

Classification of atmospheric river events on the U.S. West Coast using a trajectory model

et al. 2015

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“…Air parcels reaching the subtropics during the cold season tend to be last saturated in the extratropical storm tracks and the associated westerly jets (Galewsky et al 2005;Kelly et al 1991;Yang and Pierrehumbert 1994). Transient potential vorticity (PV) intrusions have been linked to variability of humidity in the upper troposphere (Ryoo et al 2008), particularly over the subtropical oceans (Ryoo et al 2008;Waugh 2005;Waugh and Funatsu 2003). They attributed the aridity over the subtropical eastern Pacific to final dehydration both in the midlatitudes and in the tropical upper troposphere.…”

Section: Introductionmentioning

confidence: 99%

A Last Saturation Analysis of ENSO Humidity Variability in the Subtropical Pacific

Hurley

Galewsky

2010

Journal of Climate

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Water vapor tracers of last saturation were used in an atmospheric tracer transport model to evaluate ENSO variability in the generation of the dry air that defines the subtropical middle troposphere over the North Pacific. Fifteen Northern Hemisphere winters, including El Niñ o, La Niñ a, and ENSO-neutral seasons, were evaluated using both Northern Hemisphere and global last saturation water vapor tracer configurations. During El Niñ o northern winter, the free troposphere over the subtropical North Pacific is both drier and warmer than during La Niñ a.The probability distributions of the last saturation position for the dry air in the middle troposphere were evaluated over the subtropical North Pacific and were found to be further poleward, at a higher altitude, and more westerly in their components during the warm phase compared to the cold phase. During warm phase (cold phase) northern winter, 57% (49%) of the air at 208N and 633 hPa over the North Pacific was last saturated poleward of 208N and above 500 hPa. Coherency was demonstrated between tropical sea surface temperatures, extratropical atmospheric saturation, and subtropical aridity of the middle troposphere. The stronger westerly component of last saturation during the warm phase ties ENSO-variable subtropical aridity to midlatitude westerlies when there is enhanced baroclinicity and an equatorward migration of the Pacific storm track.Humidity reconstructions from the water vapor tracers capture observed ENSO humidity variability and demonstrate that it can be explained in terms of changes in the location of last saturation, and not by changes in the temperature field. This study shows how teleconnections between the tropical ocean and the extratropical upper troposphere can impact the humidity of the middle troposphere of the subtropical dry regions.

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“…The simulations by Dessler and Sherwood (2000) suggested the importance of realistic three-dimensional large-scale wind fields to accurately predict the variations of UTRH. Ryoo et al (2008) reported poleward advection associated with the PV intrusion as a potential mechanism for the UTRH enhancement. Consistent with this, in the present study, the wind vector at 350 K isentropic level shows the flow from low to high latitudes to the east of the PV intrusion.…”

Section: Discussionmentioning

confidence: 99%

“…Folkins and Appenzeller (1996) and Baray et al (1998) observed sudden changes in ozone mixing ratio at tropical latitudes in connection with the PV intrusion. Ryoo et al (2008) studied the variability of subtropical UTRH during the northern winter and reported that both convection and poleward advection during PV intrusions could contribute towards increase in UTRH. However, we present four cases here, in which even tropical UTRH variations are shown to be dependent on the northward advection associated with the PV intrusions irrespective of whether the intrusions are accompanied by deep convection or not.…”

Section: Introductionmentioning

confidence: 99%

Tropical upper tropospheric humidity variations due to potential vorticity intrusions

2015

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Abstract. Four cases (March 2009, May 2009, April 2010 and February 2012 are presented in which the ERA-interim relative humidity (RH) shows consistent increase by more than 50 % in the upper troposphere (200-250 hPa) over tropics at the eastward side of the potential vorticity (PV) intrusion region. The increase in RH is confirmed with the spaceborne microwave limb sounder observations and radiosonde observations over Gadanki (13.5 • N, 79.2 • E) and is observed irrespective of whether the PV intrusions are accompanied by deep convection or not. It is demonstrated that the increase in RH is due to poleward advection induced by the PV intrusions in their eastward side at the upper tropospheric heights. It is suggested that the low-latitude convection, which is not necessarily triggered by the PV intrusion, might have transported water vapour to the upper tropospheric heights.

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Variability of subtropical upper tropospheric humidity

Cited by 19 publications

References 40 publications

Classification of atmospheric river events on the U.S. West Coast using a trajectory model

Classification of atmospheric river events on the U.S. West Coast using a trajectory model

A Last Saturation Analysis of ENSO Humidity Variability in the Subtropical Pacific

Tropical upper tropospheric humidity variations due to potential vorticity intrusions

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