scholarly journals Mechanisms of Summertime Subtropical Southern Indian Ocean Sea Surface Temperature Variability: On the Importance of Humidity Anomalies and the Meridional Advection of Water Vapor*

2007 ◽  
Vol 20 (19) ◽  
pp. 4835-4852 ◽  
Author(s):  
A. M. Chiodi ◽  
D. E. Harrison
Keyword(s):  
Heat Flux ◽  
Water Vapor ◽  
Indian Ocean ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Latent Heat Flux ◽  
Sea Surface ◽  
Sst Variability ◽  
Flux Variability ◽  
Meridional Advection

Abstract It is well known that some austral summertime subtropical Indian Ocean sea surface temperature (SST) variability correlates with rainfall over certain regions of Africa that depend on rainfall for their economic well-being. Recent studies have determined that this SST variability is at least partially driven by latent heat flux variability, but the mechanism has not been fully described. Here, the mechanism that drives this SST variability is reexamined using analyses of operational air–sea fluxes, ocean mixed layer modeling, and simple atmospheric boundary layer physics. The SST variability of interest is confirmed to be mainly driven by latent heat flux variability, which is shown, for the first time, to be mainly caused by near-surface humidity variability. This humidity variability is then shown to be fundamentally driven by the anomalous meridional advection of water vapor. The meridional wind anomalies of interest are subsequently found to occur when the subtropical atmospheric anticyclone is preferentially located toward one of the sides (east/west) of the basin.

scholarly journals Latent Heat Flux Sensitivity to Sea Surface Temperature: Regional Perspectives

2017 ◽  
Vol 30 (1) ◽  
pp. 129-143 ◽  
Author(s):  
B. Praveen Kumar ◽  
Meghan F. Cronin ◽  
Sudheer Joseph ◽  
M. Ravichandran ◽  
N. Sureshkumar
Keyword(s):  
Heat Flux ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Global Analysis ◽  
Surface Wind ◽  
Sea Surface ◽  
State Variables ◽  
Monsoon Period

A global analysis of latent heat flux (LHF) sensitivity to sea surface temperature (SST) is performed, with focus on the tropics and the north Indian Ocean (NIO). Sensitivity of LHF state variables (surface wind speed Ws and vertical humidity gradients Δq) to SST give rise to mutually interacting dynamical (Ws driven) and thermodynamical (Δq driven) coupled feedbacks. Generally, LHF sensitivity to SST is pronounced over tropics where SST increase causes Ws (Δq) changes, resulting in a maximum decrease (increase) of LHF by ~15 W m−2 (°C)−1. But the Bay of Bengal (BoB) and north Arabian Sea (NAS) remain an exception that is opposite to the global feedback relationship. This uniqueness is attributed to strong seasonality in monsoon Ws and Δq variations, which brings in warm (cold) continental air mass into the BoB and NAS during summer (winter), producing a large seasonal cycle in air–sea temperature difference ΔT (and hence in Δq). In other tropical oceans, surface air is mostly of marine origin and blows from colder to warmer waters, resulting in a constant ΔT ~ 1°C throughout the year, and hence a constant Δq. Thus, unlike other basins, when the BoB and NAS are warming, air temperature warms faster than SST. The resultant decrease in ΔT and Δq contributes to decrease the LHF with increased SST, contrary to other basins. This analysis suggests that, in the NIO, LHF variability is largely controlled by thermodynamic processes, which peak during the monsoon period. These observed LHF sensitivities are then used to speculate how the surface energetics and coupled feedbacks may change in a warmer world.

scholarly journals Coupling Ocean Currents and Waves with Wind Stress over the Gulf Stream

2019 ◽  
Vol 11 (12) ◽  
pp. 1476 ◽  
Author(s):  
Qi Shi ◽  
Mark A. Bourassa
Keyword(s):  
Heat Flux ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Latent Heat Flux ◽  
Wind Stress ◽  
Gulf Stream ◽  
Satellite Observations ◽  
Sea Surface ◽  
Current Stress ◽  
Induced Changes

This study provides the first detailed analysis of oceanic and atmospheric responses to the current-stress, wave-stress, and wave-current-stress interactions around the Gulf Stream using a high-resolution three-way coupled regional modeling system. In general, our results highlight the substantial impact of coupling currents and/or waves with wind stress on the air–sea fluxes over the Gulf Stream. The stress and the curl of the stress are crucial to mixed-layer energy budgets and sea surface temperature. In the wave-current-stress coupled experiment, wind stress increased by 15% over the Gulf Stream. Alternating positive and negative bands of changes of Ekman-related vertical velocity appeared in response to the changes of the wind stress curl along the Gulf Stream, with magnitudes exceeding 0.3 m/day (the 95th percentile). The response of wind stress and its curl to the wave-current-stress coupling was not a linear combination of responses to the wave-stress coupling and the current-stress coupling because the ocean and wave induced changes in the atmosphere showed substantial feedback on the ocean. Changes of a latent heat flux in excess of 20 W/m2 and a sensible heat flux in excess of 5 W/m2 were found over the Gulf Stream in all coupled experiments. Sensitivity tests show that sea surface temperature (SST) induced difference of air–sea humidity is a major contributor to latent heat flux (LHF) change. Validation is challenging because most satellite observations lack the spatial resolution to resolve the current-induced changes in wind stress curls and heat fluxes. Scatterometer observations can be used to examine the changes in wind stress across the Gulf Stream. The conversion of model data to equivalent neutral winds is highly dependent on the physics considered in the air–sea turbulent fluxes, as well as air–sea temperature differences. This sensitivity is shown to be large enough that satellite observations of winds can be used to test the flux parameterizations in coupled models.

scholarly journals Meteorological impacts of sea-surface temperature associated with the humid airflow from Tropical Cyclone Talas (2011)

2014 ◽  
Vol 32 (7) ◽  
pp. 841-857 ◽  
Author(s):  
M. Yamamoto
Keyword(s):  
Heat Flux ◽  
Tropical Cyclone ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Surface Wind ◽  
Sea Surface ◽  
Horizontal Wind ◽  
Sst Anomaly

Abstract. This paper examines meteorological impacts of sea-surface temperature (SST) in the presence of the humid airflow from Tropical Cyclone Talas (2011). To investigate the influence of the SST on the severe weather in and around Japan, sensitivity simulations were conducted using six SST data products covering a period of 7 days. The upward sea-surface latent heat flux that accumulated over the 7-day period was high around the Kuroshio during the slow passage of the tropical cyclone. Large differences were found among the individual SST products around the southern coast of Japan. The coastal warm SST anomaly of ~ 1.5 °C enhanced the surface upward latent heat fluxes (by 60 to 80%), surface southeasterly winds (by 6 to 8%), and surface water mixing ratios (by 4%) over the coastal sea area. The enhanced latent heat flux resulting from the coastal SST anomaly contributed to the further enhancement of the latent heat flux itself via a positive feedback with the amplified surface horizontal wind. The SST anomalies produced an anomaly in 7-day precipitation (ca. 40 mm) along the mountainsides and over a coastal area where the surface wind anomaly was locally large. Thus, coastal SST error is important in the atmospheric simulation of accumulated evaporation and precipitation associated with tropical cyclones making landfall.

Daily to Decadal Sea Surface Temperature Variability Driven by State-Dependent Stochastic Heat Fluxes

2006 ◽  
Vol 36 (10) ◽  
pp. 1940-1958 ◽  
Author(s):  
Philip Sura ◽  
Matthew Newman ◽  
Michael A. Alexander
Keyword(s):  
Heat Flux ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Mixed Layer ◽  
Multiplicative Noise ◽  
The State ◽  
Sea Surface ◽  
Sst Variability ◽  
State Dependent ◽  
Sst Anomalies

Abstract The classic Frankignoul–Hasselmann hypothesis for sea surface temperature (SST) variability of an oceanic mixed layer assumes that the surface heat flux can be simply parameterized as noise induced by atmospheric variability plus a linear temperature relaxation rate. It is suggested here, however, that rapid fluctuations in this rate, as might be expected, for example, from gustiness of the sea surface winds, are large enough that they cannot be ignored. Such fluctuations cannot be fully modeled by noise that is independent of the state of the SST anomaly itself. Rather, they require the inclusion of a state-dependent (i.e., multiplicative) noise term, which can be expected to affect both persistence and the relative occurrence of high-amplitude anomalies. As a test of this hypothesis, daily observations at several Ocean Weather Stations (OWSs) are examined. Significant skewness and kurtosis of the distributions of SST anomalies is found, which is shown to be consistent with a multiplicative noise model. The observed wintertime SST distribution at OWS P is reproduced using a single-column variable-depth mixed layer model; the resulting non-Gaussianity is found to be largely due to the state dependence of rapidly varying (effectively stochastic) sensible and latent heat flux anomalies. The authors’ model for the non-Gaussianity of anomalous SST variability (counterintuitively) implies that the multiplicative noise increases the persistence, predictability, and variance of midlatitude SST anomalies. The effect is strongest on annual and longer time scales and may, therefore, be important to the understanding and modeling of interannual and interdecadal SST and related climate variability.

The Behavior of the Bulk – Skin Sea Surface Temperature Difference under Varying Wind Speed and Heat Flux

1996 ◽  
Vol 26 (10) ◽  
pp. 1969-1988 ◽  
Author(s):  
Gary A. Wick ◽  
William J. Emery ◽  
Lakshmi H. Kantha ◽  
Peter Schlüssel
Keyword(s):  
Heat Flux ◽  
Wind Speed ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Temperature Difference ◽  
Sea Surface

scholarly journals Interannual Variability of Sea Surface Temperature off Java and Sumatra in a Global GCM*

2008 ◽  
Vol 21 (11) ◽  
pp. 2451-2465 ◽  
Author(s):  
Yan Du ◽  
Tangdong Qu ◽  
Gary Meyers
Keyword(s):  
Indian Ocean ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Mixed Layer ◽  
Heat Budget ◽  
Sea Surface ◽  
Surface Mixed Layer ◽  
Horizontal Advection ◽  
Cold Anomaly ◽  
Sst Anomalies

Abstract Using results from the Simple Ocean Data Assimilation (SODA), this study assesses the mixed layer heat budget to identify the mechanisms that control the interannual variation of sea surface temperature (SST) off Java and Sumatra. The analysis indicates that during the positive Indian Ocean Dipole (IOD) years, cold SST anomalies are phase locked with the season cycle. They may exceed −3°C near the coast of Sumatra and extend as far westward as 80°E along the equator. The depth of the thermocline has a prominent influence on the generation and maintenance of SST anomalies. In the normal years, cooling by upwelling–entrainment is largely counterbalanced by warming due to horizontal advection. In the cooling episode of IOD events, coastal upwelling–entrainment is enhanced, and as a result of mixed layer shoaling, the barrier layer no longer exists, so that the effect of upwelling–entrainment can easily reach the surface mixed layer. Horizontal advection spreads the cold anomaly to the interior tropical Indian Ocean. Near the coast of Java, the northern branch of an anomalous anticyclonic circulation spreads the cold anomaly to the west near the equator. Both the anomalous advection and the enhanced, wind-driven upwelling generate the cold SST anomaly of the positive IOD. At the end of the cooling episode, the enhanced surface thermal forcing overbalances the cooling effect by upwelling/entrainment, and leads to a warming in SST off Java and Sumatra.

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