Atmospheric moisture transport and river runoff in the mid-latitudes

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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Roles of the Rocky Mountains in the Atlantic and Pacific Meridional Overturning Circulations

Journal of Climate ◽

10.1175/jcli-d-20-0819.1 ◽

2021 ◽

pp. 1-41

Author(s):

Rui Jiang ◽

Haijun Yang

Keyword(s):

North Atlantic ◽

Rocky Mountains ◽

North Pacific ◽

Moisture Transport ◽

Atmospheric Moisture ◽

The North ◽

Meridional Overturning ◽

The North Atlantic ◽

The North Pacific ◽

Atmospheric Moisture Transport

AbstractThe effect of the Rocky Mountains (RM) on meridional overturning circulations (MOCs) is investigated using a fully coupled climate model. Located between the Atlantic and Pacific oceans, the RM is the major mountains in North America. It presence plays an important role in atmospheric moisture transport between the two oceans. Adding the RM to a flat global continent (OnlyRocky) leads to a weakening of the atmospheric moisture transport from the North Pacific to the North Atlantic, which is consistent with previous finding. However, the simulation also shows more atmospheric moisture is transported from the tropical Pacific and Atlantic to the North Atlantic. The net effect of moisture transport leads to a slight freshening of the North Atlantic. The Atlantic MOC (AMOC) is hardly changed, but the Pacific MOC (PMOC) declines by 40% due to more moisture retained in the North Pacific. The sensitivity experiment of removing the RM from a realistic global topography (NoRocky) gives roughly opposite atmospheric changes to the OnlyRocky experiment. The AMOC in NoRocky declines slightly and then recovers, while the PMOC is nearly unchanged. The paired experiments conducted in this study demonstrate that the presence of the RM plays a trivial role in Northern Hemisphere deep-water formation.

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Changes in Normalized Difference Vegetation Index in the Orinoco and Amazon River Basins: Links to Tropical Atlantic Surface Temperatures

Journal of Climate ◽

10.1175/jcli-d-19-0696.1 ◽

2020 ◽

Vol 33 (19) ◽

pp. 8537-8559

Author(s):

Paola A. Arias ◽

J. Alejandro Martínez ◽

Juan David Mejía ◽

María José Pazos ◽

Jhan Carlo Espinoza ◽

...

Keyword(s):

Soil Moisture ◽

Atlantic Ocean ◽

Moisture Transport ◽

Vegetation Index ◽

Normalized Difference Vegetation Index ◽

Dominant Role ◽

Atmospheric Moisture ◽

Moisture Recycling ◽

Surface Temperatures ◽

Atmospheric Moisture Transport

AbstractWe analyze the observed relationship between sea surface temperatures (SSTs) over the Atlantic Ocean and the normalized difference vegetation index (NDVI) in the Orinoco and Amazon basins. Monthly correlations between anomalies of NDVI and SSTs are computed for different regions of the Atlantic Ocean. We also use a mixture of observations and reanalysis products to analyze lagged correlations. Our results show that during August–September (i.e., the dry-to-wet transition season), changes in NDVI in the central Amazon and the so-called Arc of Deforestation are associated with precedent changes in the SSTs of the tropical North Atlantic (TNA) and the Caribbean (CABN) during March–June. Anomalous warming of the CABN and TNA generates changes in surface winds and atmospheric moisture transport in the region, decreasing precipitation, with consequent decreases of soil moisture, moisture recycling, and NDVI. An increase in TNA and CABN SSTs during March–June is also associated with an increase of NDVI over the northern Orinoco during June (i.e., the wet season). Unlike in the southern Amazon, precipitation and soil moisture in the Orinoco basin do not exhibit significant changes associated with SSTs. By contrast, atmospheric moisture recycling and transport increase with warmer SSTs in the TNA. Therefore, for the Orinoco, the link between SSTs and NDVI appears to be related not to changes in precipitation but to changes in moisture recycling. However, the causality between these changes needs to be further explored. These findings highlight the contrasting responses of the Amazon and Orinoco basins to Atlantic temperatures and the dominant role of atmospheric moisture transport linking these responses.

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