ABSTRACT Weddell Sea Warm Deep Water (WDW) circulates anti-cyclonically in the Weddell gyre, cool... more ABSTRACT Weddell Sea Warm Deep Water (WDW) circulates anti-cyclonically in the Weddell gyre, cooling as it does so. WDW is fed by Circumpolar Deep Water (CDW) that bifurcates between 40°E and 80°E from the Antarctic Circumpolar Current (ACC). WDW is remarkably stable in its theta and salinity properties with no statistically significant trend over the last three decades. Small decadal variability is superimposed. A different state of the Weddell Sea gyre is found in the late-70ies and early-80ies, with significant colder temperatures downstream of the CDW bifurcation. The decadal variations are correlated with the Southern Annular Mode (SAM), in particular the meridional atmospheric pressure gradient in the Atlantic sector. We propose this occurs due to a reduction in the supply of new WDW into the Weddell gyre during times of negative SAM. Impact of the WDW-SAM connection on AABW and polynya formation is discussed.
ABSTRACT Many studies have noted decadal scale sea surface temperature (SST) variability in the N... more ABSTRACT Many studies have noted decadal scale sea surface temperature (SST) variability in the North Pacific Ocean. The spatial SST pattern has a cold anomaly in the central North Pacific that extends to the Pacific western boundary and resembles a broader and weaker El Nino signal in the tropics. This pattern of variability is often referred to as the Pacific Decadal Oscillation (PDO). Despite extensive research, the nature of the apparent oscillation between warm and cold SST anomalies in the central North Pacific is still surrounded by much uncertainty. A generally agreed upon point is that decadal-scale SST variability appears to be somehow linked to El Nino. However, the mechanism by which such variability is generated, be it an independent dynamical process or a stochastic reddening of other climate signals, is not well understood. Decadal variability in the North Pacific has impacts both locally and remotely. Temperature changes in the North Pacific can have a significant effect on the local ecosystem. Remote effects of the PDO include changes to the surface climate (e.g., temperature and precipitation) in Australia, South and North America, the Russian Far East, much of eastern Asia, and the maritime continent. Improved understanding of decadal variability in the North Pacific could lead to a better understanding of climate variability in these remote regions. Here we use a state-of-the-art high-resolution coupled climate model, HiGEM, to show that anomalous ocean transport in the North Pacific can largely account for the decadal-scale SST variability. We also demonstrate that it is likely that the same mechanism occurs in the real ocean, and therefore that internal ocean dynamics play a key role in regulating decadal-scale variability in the North Pacific.
The Bay of Bengal (BoB) generally exhibits surface oligotrophy due to nutrient limitation induced... more The Bay of Bengal (BoB) generally exhibits surface oligotrophy due to nutrient limitation induced by strong salinity stratification. Nevertheless, there are hotspots of high chlorophyll in the BoB where the monsoonal forcings are strong enough to break the stratification; one such region is the southern BoB, east of Sri Lanka. A recent field programme conducted during the summer monsoon of 2016, as a part of the Bay of Bengal Boundary Layer Experiment (BoBBLE), provides a unique high-resolution dataset of the vertical distribution of chlorophyll in the southern BoB using ocean gliders along with shipboard conductivity-temperature-depth (CTD) measurements. Observations were carried out for a duration of 12-20 days, covering the dynamically active regions of the Sri Lanka Dome (SLD) and the Southwest Monsoon Current (SMC). Mixing and up-welling induced by the monsoonal wind forcing enhanced surface chlorophyll concentrations (0.3-0.7 mg m −3). Prominent deep chlorophyll maxima (DCM; 0.3-1.2 mg m −3) existed at intermediate depths (20-50 m), signifying the contribution of subsurface productivity to the biological carbon cycling in the BoB. The shape of chlorophyll profiles varied in different dynamical regimes; upwelling was associated with sharp and intense DCM, whereas mixing resulted in a diffuse and weaker DCM. Within the SLD, open-ocean Ekman suction favoured a substantial increase in chlorophyll. Farther east, where the thermocline was deeper, enhanced surface chlorophyll was associated with intermittent mixing events. Remote forcing by the westward propagating Rossby waves influenced the upper-ocean dynamics and chlorophyll distribution in the southern BoB. Stabilizing surface freshening events and barrier-layer formation often inhibited the generation of surface chlorophyll. The pathway of the SMC intrusion was marked by a distinct band of chlorophyll, indicating the advective effect of biologically rich Arabian Sea waters. The region of the monsoon current exhibited the strongest DCM as well as the highest column-integrated chlorophyll. Observations suggest that the persistence of DCM in the southern BoB is promoted by surface oligotrophy and shallow mixed layers. Results from a coupled physical-ecosystem model substantiate the dominant role of mixed layer processes associated with the monsoon in controlling the nutrient distribution and biological productivity in the southern BoB. The present study provides new insights into the vertical distribution of chlorophyll in the BoB, emphasizing the need for extensive in situ sampling and ecosystem model-based efforts for a better understanding of the biophysical interactions and the potential climatic feedbacks.
Page 1. There was probably more nitrogen in the Archean atmosphere - this would have helped resol... more Page 1. There was probably more nitrogen in the Archean atmosphere - this would have helped resolve the Faint Young Sun paradox COLIN GOLDBLATT 1*, ADRIAN J. MATTHEWS 2, MARK CLAIRE 3, TIMOTHY M. LENTON ...
ABSTRACT The Maritime Continent is a highly-populated region of many islands and shallow oceans, ... more ABSTRACT The Maritime Continent is a highly-populated region of many islands and shallow oceans, located in the oceanic warm pool, between the Indian and Pacific Oceans. A strong diurnal cycle of precipitation exists due to onshore breezes causing strong convergence of moist air - enhanced by topographic effects - over the land during the day time, peaking during afternoon-evening. The respective diurnal cycle over the ocean is far weaker and does not peak until early in the morning. On intra-seasonal time-scales the greatest source of variability in the tropics is the Madden-Julian Oscillation (MJO). The convectively active part of the MJO propagates slowly (~5 ms-1) eastward through the warm pool from the Indian Ocean to the western Pacific, followed by the convectively suppressed part. The complex topography of the Maritime Continent means the exact nature of the propagation through this region is unclear. Model simulations of the MJO are often poor over the region, leading to errors in latent heat release and, subsequently, global errors in medium-range weather prediction and climate simulation. Using 14 northern hemisphere winters of high-resolution satellite data it is shown that, over regions where the diurnal cycle is strong, more than 80% of the variance in precipitation during an MJO cycle is accounted for by changes in the amplitude of the diurnal cycle. A canonical view of the MJO is of smooth eastward progression of a large-scale precipitation envelope over the warm pool. However, by computing "MJO harmonics" it is shown that the leading edge of the precipitation envelope advances over the islands of the Maritime Continent approximately 6 days or 2000 km ahead of the main body. This behaviour can be accommodated within existing theories of MJO propagation. When the active convective MJO envelope is over the eastern Indian Ocean, frictional moisture convergence and topographic blocking in the easterlies of the equatorial Kelvin wave response supply moisture to the islands of the Maritime Continent. When combined with the relatively clear skies and strong short-wave flux, the low thermal inertia of the islands allows a rapid response in the diurnal cycle which rectifies onto the lower-frequency MJO. Hence, an accurate representation of the diurnal cycle and its scale interaction appear to be necessary ingredients for models to simulate the MJO successfully.
Quarterly Journal of the Royal Meteorological Society, 2011
Page 1. Quarterly Journal of the Royal Meteorological Society QJR Meteorol. Soc. (2011) The diurn... more Page 1. Quarterly Journal of the Royal Meteorological Society QJR Meteorol. Soc. (2011) The diurnal cycle of precipitation over the Maritime Continent in a high-resolution atmospheric model Barnaby S. Love,a*Adrian J. Matthewsab ...
ABSTRACT During austral summer, the majority of precipitation over the Pacific Ocean is concentra... more ABSTRACT During austral summer, the majority of precipitation over the Pacific Ocean is concentrated in the South Pacific Convergence Zone (SPCZ). The surface boundary conditions required to support the diagonally (northwest-southeast) oriented SPCZ are determined through a series of experiments with an atmospheric general circulation model. Continental configuration and orography do not have a significant influence on SPCZ orientation and strength. The key necessary boundary condition is the zonally asymmetric component of the sea surface temperature (SST) distribution. This leads to a strong subtropical anticyclone over the southeast Pacific that, on its western flank, transports warm moist air from the equator into the SPCZ region. This moisture then intensifies (diagonal) bands of convection that are initiated by regions of ascent and reduced static stability ahead of the cyclonic vorticity in Rossby waves that are refracted toward the westerly duct over the equatorial Pacific. The climatological SPCZ is comprised of the superposition of these diagonal bands of convection. When the zonally asymmetric SST component is reduced or removed, the subtropical anticyclone and its associated moisture source is weakened. Despite the presence of Rossby waves, significant moist convection is no longer triggered; the SPCZ disappears. The diagonal SPCZ is robust to large changes (up to ±6 °C) in absolute SST (i.e. where the SST asymmetry is preserved). Extreme cooling (change
Quarterly Journal of the Royal Meteorological Society, 2008
Page 1. QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY QJR Meteorol. Soc. 134: 439453 (20... more Page 1. QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY QJR Meteorol. Soc. 134: 439453 (2008) Published online 2 April 2008 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/qj.224 ...
Jenni Barclay School of Environmental Sciences, University of East Anglia, Norwich, UK Received 1... more Jenni Barclay School of Environmental Sciences, University of East Anglia, Norwich, UK Received 17 December 2003; revised 4 February 2004; accepted 13 February 2004; published 12 March 2004. [1] Dome-forming volcanic eruptions typically involve the slow extrusion of viscous ...
ABSTRACT Weddell Sea Warm Deep Water (WDW) circulates anti-cyclonically in the Weddell gyre, cool... more ABSTRACT Weddell Sea Warm Deep Water (WDW) circulates anti-cyclonically in the Weddell gyre, cooling as it does so. WDW is fed by Circumpolar Deep Water (CDW) that bifurcates between 40°E and 80°E from the Antarctic Circumpolar Current (ACC). WDW is remarkably stable in its theta and salinity properties with no statistically significant trend over the last three decades. Small decadal variability is superimposed. A different state of the Weddell Sea gyre is found in the late-70ies and early-80ies, with significant colder temperatures downstream of the CDW bifurcation. The decadal variations are correlated with the Southern Annular Mode (SAM), in particular the meridional atmospheric pressure gradient in the Atlantic sector. We propose this occurs due to a reduction in the supply of new WDW into the Weddell gyre during times of negative SAM. Impact of the WDW-SAM connection on AABW and polynya formation is discussed.
ABSTRACT Many studies have noted decadal scale sea surface temperature (SST) variability in the N... more ABSTRACT Many studies have noted decadal scale sea surface temperature (SST) variability in the North Pacific Ocean. The spatial SST pattern has a cold anomaly in the central North Pacific that extends to the Pacific western boundary and resembles a broader and weaker El Nino signal in the tropics. This pattern of variability is often referred to as the Pacific Decadal Oscillation (PDO). Despite extensive research, the nature of the apparent oscillation between warm and cold SST anomalies in the central North Pacific is still surrounded by much uncertainty. A generally agreed upon point is that decadal-scale SST variability appears to be somehow linked to El Nino. However, the mechanism by which such variability is generated, be it an independent dynamical process or a stochastic reddening of other climate signals, is not well understood. Decadal variability in the North Pacific has impacts both locally and remotely. Temperature changes in the North Pacific can have a significant effect on the local ecosystem. Remote effects of the PDO include changes to the surface climate (e.g., temperature and precipitation) in Australia, South and North America, the Russian Far East, much of eastern Asia, and the maritime continent. Improved understanding of decadal variability in the North Pacific could lead to a better understanding of climate variability in these remote regions. Here we use a state-of-the-art high-resolution coupled climate model, HiGEM, to show that anomalous ocean transport in the North Pacific can largely account for the decadal-scale SST variability. We also demonstrate that it is likely that the same mechanism occurs in the real ocean, and therefore that internal ocean dynamics play a key role in regulating decadal-scale variability in the North Pacific.
The Bay of Bengal (BoB) generally exhibits surface oligotrophy due to nutrient limitation induced... more The Bay of Bengal (BoB) generally exhibits surface oligotrophy due to nutrient limitation induced by strong salinity stratification. Nevertheless, there are hotspots of high chlorophyll in the BoB where the monsoonal forcings are strong enough to break the stratification; one such region is the southern BoB, east of Sri Lanka. A recent field programme conducted during the summer monsoon of 2016, as a part of the Bay of Bengal Boundary Layer Experiment (BoBBLE), provides a unique high-resolution dataset of the vertical distribution of chlorophyll in the southern BoB using ocean gliders along with shipboard conductivity-temperature-depth (CTD) measurements. Observations were carried out for a duration of 12-20 days, covering the dynamically active regions of the Sri Lanka Dome (SLD) and the Southwest Monsoon Current (SMC). Mixing and up-welling induced by the monsoonal wind forcing enhanced surface chlorophyll concentrations (0.3-0.7 mg m −3). Prominent deep chlorophyll maxima (DCM; 0.3-1.2 mg m −3) existed at intermediate depths (20-50 m), signifying the contribution of subsurface productivity to the biological carbon cycling in the BoB. The shape of chlorophyll profiles varied in different dynamical regimes; upwelling was associated with sharp and intense DCM, whereas mixing resulted in a diffuse and weaker DCM. Within the SLD, open-ocean Ekman suction favoured a substantial increase in chlorophyll. Farther east, where the thermocline was deeper, enhanced surface chlorophyll was associated with intermittent mixing events. Remote forcing by the westward propagating Rossby waves influenced the upper-ocean dynamics and chlorophyll distribution in the southern BoB. Stabilizing surface freshening events and barrier-layer formation often inhibited the generation of surface chlorophyll. The pathway of the SMC intrusion was marked by a distinct band of chlorophyll, indicating the advective effect of biologically rich Arabian Sea waters. The region of the monsoon current exhibited the strongest DCM as well as the highest column-integrated chlorophyll. Observations suggest that the persistence of DCM in the southern BoB is promoted by surface oligotrophy and shallow mixed layers. Results from a coupled physical-ecosystem model substantiate the dominant role of mixed layer processes associated with the monsoon in controlling the nutrient distribution and biological productivity in the southern BoB. The present study provides new insights into the vertical distribution of chlorophyll in the BoB, emphasizing the need for extensive in situ sampling and ecosystem model-based efforts for a better understanding of the biophysical interactions and the potential climatic feedbacks.
Page 1. There was probably more nitrogen in the Archean atmosphere - this would have helped resol... more Page 1. There was probably more nitrogen in the Archean atmosphere - this would have helped resolve the Faint Young Sun paradox COLIN GOLDBLATT 1*, ADRIAN J. MATTHEWS 2, MARK CLAIRE 3, TIMOTHY M. LENTON ...
ABSTRACT The Maritime Continent is a highly-populated region of many islands and shallow oceans, ... more ABSTRACT The Maritime Continent is a highly-populated region of many islands and shallow oceans, located in the oceanic warm pool, between the Indian and Pacific Oceans. A strong diurnal cycle of precipitation exists due to onshore breezes causing strong convergence of moist air - enhanced by topographic effects - over the land during the day time, peaking during afternoon-evening. The respective diurnal cycle over the ocean is far weaker and does not peak until early in the morning. On intra-seasonal time-scales the greatest source of variability in the tropics is the Madden-Julian Oscillation (MJO). The convectively active part of the MJO propagates slowly (~5 ms-1) eastward through the warm pool from the Indian Ocean to the western Pacific, followed by the convectively suppressed part. The complex topography of the Maritime Continent means the exact nature of the propagation through this region is unclear. Model simulations of the MJO are often poor over the region, leading to errors in latent heat release and, subsequently, global errors in medium-range weather prediction and climate simulation. Using 14 northern hemisphere winters of high-resolution satellite data it is shown that, over regions where the diurnal cycle is strong, more than 80% of the variance in precipitation during an MJO cycle is accounted for by changes in the amplitude of the diurnal cycle. A canonical view of the MJO is of smooth eastward progression of a large-scale precipitation envelope over the warm pool. However, by computing "MJO harmonics" it is shown that the leading edge of the precipitation envelope advances over the islands of the Maritime Continent approximately 6 days or 2000 km ahead of the main body. This behaviour can be accommodated within existing theories of MJO propagation. When the active convective MJO envelope is over the eastern Indian Ocean, frictional moisture convergence and topographic blocking in the easterlies of the equatorial Kelvin wave response supply moisture to the islands of the Maritime Continent. When combined with the relatively clear skies and strong short-wave flux, the low thermal inertia of the islands allows a rapid response in the diurnal cycle which rectifies onto the lower-frequency MJO. Hence, an accurate representation of the diurnal cycle and its scale interaction appear to be necessary ingredients for models to simulate the MJO successfully.
Quarterly Journal of the Royal Meteorological Society, 2011
Page 1. Quarterly Journal of the Royal Meteorological Society QJR Meteorol. Soc. (2011) The diurn... more Page 1. Quarterly Journal of the Royal Meteorological Society QJR Meteorol. Soc. (2011) The diurnal cycle of precipitation over the Maritime Continent in a high-resolution atmospheric model Barnaby S. Love,a*Adrian J. Matthewsab ...
ABSTRACT During austral summer, the majority of precipitation over the Pacific Ocean is concentra... more ABSTRACT During austral summer, the majority of precipitation over the Pacific Ocean is concentrated in the South Pacific Convergence Zone (SPCZ). The surface boundary conditions required to support the diagonally (northwest-southeast) oriented SPCZ are determined through a series of experiments with an atmospheric general circulation model. Continental configuration and orography do not have a significant influence on SPCZ orientation and strength. The key necessary boundary condition is the zonally asymmetric component of the sea surface temperature (SST) distribution. This leads to a strong subtropical anticyclone over the southeast Pacific that, on its western flank, transports warm moist air from the equator into the SPCZ region. This moisture then intensifies (diagonal) bands of convection that are initiated by regions of ascent and reduced static stability ahead of the cyclonic vorticity in Rossby waves that are refracted toward the westerly duct over the equatorial Pacific. The climatological SPCZ is comprised of the superposition of these diagonal bands of convection. When the zonally asymmetric SST component is reduced or removed, the subtropical anticyclone and its associated moisture source is weakened. Despite the presence of Rossby waves, significant moist convection is no longer triggered; the SPCZ disappears. The diagonal SPCZ is robust to large changes (up to ±6 °C) in absolute SST (i.e. where the SST asymmetry is preserved). Extreme cooling (change
Quarterly Journal of the Royal Meteorological Society, 2008
Page 1. QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY QJR Meteorol. Soc. 134: 439453 (20... more Page 1. QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY QJR Meteorol. Soc. 134: 439453 (2008) Published online 2 April 2008 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/qj.224 ...
Jenni Barclay School of Environmental Sciences, University of East Anglia, Norwich, UK Received 1... more Jenni Barclay School of Environmental Sciences, University of East Anglia, Norwich, UK Received 17 December 2003; revised 4 February 2004; accepted 13 February 2004; published 12 March 2004. [1] Dome-forming volcanic eruptions typically involve the slow extrusion of viscous ...
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