Vertical Structure of the Upper–Indian Ocean Thermal Variability

2020 ◽  
Vol 33 (17) ◽  
pp. 7233-7253 ◽  
Author(s):  
Yuanlong Li ◽  
Weiqing Han ◽  
Fan Wang ◽  
Lei Zhang ◽  
Jing Duan
Keyword(s):  
Heat Flux ◽  
Indian Ocean ◽  
Time Scale ◽  
Vertical Structure ◽  
Southern Oscillation ◽  
Linear Trend ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Shortwave Radiation ◽  
Turbulent Heat

AbstractMulti-time-scale variabilities of the Indian Ocean (IO) temperature over 0–700 m are revisited from the perspective of vertical structure. Analysis of historical data for 1955–2018 identifies two dominant types of vertical structures that account for respectively 70.5% and 21.2% of the total variance on interannual-to-interdecadal time scales with the linear trend and seasonal cycle removed. The leading type manifests as vertically coherent warming/cooling with the maximal amplitude at ~100 m and exhibits evident interdecadal variations. The second type shows a vertical dipole structure between the surface (0–60 m) and subsurface (60–400 m) layers and interannual-to-decadal fluctuations. Ocean model experiments were performed to gain insights into underlying processes. The vertically coherent, basinwide warming/cooling of the IO on an interdecadal time scale is caused by changes of the Indonesian Throughflow (ITF) controlled by Pacific climate and anomalous surface heat fluxes partly originating from external forcing. Enhanced changes in the subtropical southern IO arise from positive air–sea feedback among sea surface temperature, winds, turbulent heat flux, cloud cover, and shortwave radiation. Regarding dipole-type variability, the basinwide surface warming is induced by surface heat flux forcing, and the subsurface cooling occurs only in the eastern IO. The cooling in the southeast IO is generated by the weakened ITF, whereas that in the northeast IO is caused by equatorial easterly winds through upwelling oceanic waves. Both El Niño–Southern Oscillation (ENSO) and IO dipole (IOD) events are favorable for the generation of such vertical dipole anomalies.

Observed extreme air-sea heat flux variations during three tropical cyclones in the tropical southeastern Indian Ocean

2021 ◽  
pp. 1-77
Author(s):  
Xiangzhou Song ◽  
Chunlin Ning ◽  
Yongliang Duan ◽  
Huiwu Wang ◽  
Chao Li ◽  
...  
Keyword(s):  
Heat Flux ◽  
Indian Ocean ◽  
Tropical Cyclones ◽  
Heat Fluxes ◽  
Shortwave Radiation ◽  
Turbulent Heat ◽  
Maximum Magnitude ◽  
Surface Cooling ◽  
Mean Values ◽  
The Mean

AbstractSix-month buoy-based heat flux observations from the poorly sampled tropical southeastern Indian Ocean are examined to document the extremes during three tropical cyclones (TCs) from December 2018 to May 2019. The most striking feature at the mooring site (115.2°E, 16.9°S) during the TCs is the extensively suppressed diurnal cycle of net surface flux, with a mean daytime (nighttime) reduction of 470 (131) W m-2, a peak decrease at approximately noon of 695 W m-2 and an extreme drop during TC Riley of 800 W m-2. The mean surface cooling in the daytime is primarily contributed by the 370 W m-2 decrease in shortwave radiation associated with the increased cloudiness. The air-sea turbulent heat fluxes increase by approximately 151 W m-2 in response to the enhanced wind speed under near-neutral boundary conditions. The daily mean rainfall-induced cooling is 8 W m-2, with a maximum magnitude of 90 W m-2. The mean values, seasonal variation, and synoptic variability of the characteristic heat fluxes are used to assess the new reanalysis data from ERA5 and MERRA2 and the analyzed OAFlux. The overall performance of the high-frequency net heat flux estimates at the synoptic scale is satisfactory, but the four flux components exhibit different quality levels. A serious error is that ERA5 and MERRA2 poorly represent TCs, and they show significant daily mean Qnet biases with opposite directions, -59 W m-2 (largely due to the overestimated latent heat with a bias of -76 W m-2) and 50 W m-2 (largely due to the overestimated shortwave radiation with a bias of 41 W m-2), respectively.

scholarly journals Asymmetric Response of the Equatorial Pacific SST to Climate Warming and Cooling

2017 ◽  
Vol 30 (18) ◽  
pp. 7255-7270 ◽  
Author(s):  
Fukai Liu ◽  
Yiyong Luo ◽  
Jian Lu ◽  
Oluwayemi Garuba ◽  
Xiuquan Wan
Keyword(s):  
Heat Flux ◽  
Heat Budget ◽  
Dominant Role ◽  
Surface Heat ◽  
Equatorial Pacific ◽  
Heat Fluxes ◽  
Shortwave Radiation ◽  
Asymmetric Structure ◽  
Linear Component ◽  
Budget Analysis

Abstract The response of the equatorial Pacific Ocean to heat fluxes of equal amplitude but opposite sign is investigated using the Community Earth System Model (CESM). Results show a strong asymmetry in SST changes. In the eastern equatorial Pacific (EEP), the warming responding to the positive forcing exceeds the cooling response to the negative forcing, whereas in the western equatorial Pacific (WEP) it is the other way around and the cooling surpasses the warming. This leads to a zonal dipole asymmetric structure, with positive values in the east and negative values in the west. A surface heat budget analysis suggests that the SST asymmetry mainly results from the oceanic horizontal advection and vertical entrainment, with both of their linear and nonlinear components playing a role. For the linear component, its change appears to be more significant over the EEP (WEP) in the positive (negative) forcing scenario, favoring the seesaw pattern of the SST asymmetry. For the nonlinear component, its change acts to warm (cool) the EEP (WEP) in both scenarios, also favorable for the development of the SST asymmetry. Additional experiments with a slab ocean confirm the dominant role of ocean dynamical processes for this SST asymmetry. The net surface heat flux, in contrast, works to reduce the SST asymmetry through its shortwave radiation and latent heat flux components, with the former being related to the nonlinear relationship between SST and convection, and the latter being attributable to Newtonian damping and air–sea stability effects. The suppressing effect of shortwave radiation on SST asymmetry is further verified by partially coupled overriding experiments.

scholarly journals Improving Soil Moisture and Surface Turbulent Heat Flux Estimates by Assimilation of SMAP Brightness Temperatures or Soil Moisture Retrievals and GOES Land Surface Temperature Retrievals

2020 ◽  
Vol 21 (2) ◽  
pp. 183-203 ◽  
Author(s):  
Yang Lu ◽  
Susan C. Steele-Dunne ◽  
Gabriëlle J. M. De Lannoy
Keyword(s):  
Heat Flux ◽  
Soil Moisture ◽  
Surface Temperature ◽  
Land Surface Temperature ◽  
Land Surface ◽  
Surface Heat Flux ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Transfer Model ◽  
Turbulent Heat

AbstractSurface heat fluxes are vital to hydrological and environmental studies, but mapping them accurately over a large area remains a problem. In this study, brightness temperature (TB) observations or soil moisture retrievals from the NASA Soil Moisture Active Passive (SMAP) mission and land surface temperature (LST) product from the Geostationary Operational Environmental Satellite (GOES) are assimilated together into a coupled water and heat transfer model to improve surface heat flux estimates. A particle filter is used to assimilate SMAP data, while a particle smoothing method is adopted to assimilate GOES LST time series, correcting for both systematic biases via parameter updating and for short-term error via state updating. One experiment assimilates SMAP TB at horizontal polarization and GOES LST, a second experiment assimilates SMAP TB at vertical polarization and GOES LST, and a third experiment assimilates SMAP soil moisture retrievals along with GOES LST. The aim is to examine if the assimilation of physically consistent TB and LST observations could yield improved surface heat flux estimates. It is demonstrated that all three assimilation experiments improved flux estimates compared to a no-assimilation case. Assimilating TB data tends to produce smaller bias in soil moisture estimates compared to assimilating soil moisture retrievals, but the estimates are influenced by the respective bias correction approaches. Despite the differences in soil moisture estimates, the flux estimates from different assimilation experiments are in general very similar.

NFLUX Satellite-Based Surface Radiative Heat Fluxes. Part II: Gridded Products

2017 ◽  
Vol 56 (4) ◽  
pp. 1043-1057 ◽  
Author(s):  
Jackie C. May ◽  
Clark Rowley ◽  
Charlie N. Barron
Keyword(s):  
Heat Flux ◽  
Radiative Heat ◽  
Weather Prediction ◽  
Longwave Radiation ◽  
Ocean Surface ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Shortwave Radiation ◽  
Global Ocean ◽  
Clearness Index

AbstractThe Naval Research Laboratory (NRL) ocean surface flux (NFLUX) system provides near-real-time satellite-based gridded surface heat flux fields over the global ocean within hours of the observed satellite measurements. NFLUX can serve as an alternative to current numerical weather prediction models—in particular, the U. S. Navy Global Environmental Model (NAVGEM)—that provide surface forcing fields to operational ocean models. This study discusses the satellite-based shortwave and longwave global gridded analysis fields, which complete the full suite of NFLUX-provided ocean surface heat fluxes. A companion paper discusses the production of satellite swath-level surface shortwave radiation and longwave radiation estimates. The swath-level shortwave radiation estimates are converted into clearness-index values. Clearness index reduces the dependency on solar zenith angle, which allows for the assimilation of observations over a given time window. An automated quality-control process is applied to the swath-level estimates of clearness index and surface longwave radiation. Then 2D variational analyses of the quality-controlled satellite estimates with background atmospheric model fields form global gridded radiative heat flux fields. The clearness-index analysis fields are converted into shortwave analysis fields to be used in other applications. Three-hourly shortwave and longwave analysis fields are created from 1 May 2013 through 30 April 2014. These fields are validated against observations from research vessels and moored-buoy platforms and compared with NAVGEM. With the exception of the mean bias, the NFLUX fields have smaller errors when compared with those of NAVGEM.

scholarly journals Contributions of Surface Heat Fluxes and Oceanic Processes to Tropical SST Changes: Seasonal and Regional Dependence

2017 ◽  
Vol 30 (11) ◽  
pp. 4185-4205 ◽  
Author(s):  
Zhuoqi He ◽  
Renguang Wu ◽  
Weiqiang Wang ◽  
Zhiping Wen ◽  
Dongxiao Wang
Keyword(s):  
Heat Flux ◽  
Heat Budget ◽  
Spatial Scales ◽  
Geographical Area ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Shortwave Radiation ◽  
Surface Heat Fluxes ◽  
Vertical Advection ◽  
Large Geographical Area

Abstract The present study employs six surface heat flux datasets and three ocean assimilation products to assess the relative contributions of surface heat fluxes and oceanic processes to the sea surface temperature (SST) change in the tropical oceans. Large differences are identified in the major terms of the heat budget equation. The largest discrepancies among different datasets appear in the contribution of vertical advection. The heat budget is nearly balanced in the shortwave-radiation- and horizontal-advection-dominant cases but not balanced in some of the latent-heat-flux- and vertical-advection-dominant cases. The contributions of surface heat fluxes and ocean advections to the SST tendency display remarkable seasonal and regional dependence. The contribution of surface heat fluxes covers a large geographical area. The oceanic processes dominate the SST tendency in the near-equatorial regions with large values but small spatial scales. In the Pacific and Atlantic Oceans, the SST tendency is governed by the dynamic and thermodynamic processes, respectively, while a wide variety of processes contribute to the SST tendency in the Indian Ocean. Several regions have been selected to illustrate the dominant contributions of individual terms to the SST tendency in different seasons. The seasonality and regionality of the interannual air–sea relationship indicate a physical connection with the mean state.

The Effect of Soil on the Summertime Surface Energy Budget of a Humid Subarctic Tundra in Northern Quebec, Canada

2021 ◽  
Vol 22 (10) ◽  
pp. 2547-2564
Author(s):  
Georg Lackner ◽  
Daniel F. Nadeau ◽  
Florent Domine ◽  
Annie-Claude Parent ◽  
Gonzalo Leonardini ◽  
...  
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Land Surface ◽  
Sensible Heat Flux ◽  
Arctic Region ◽  
Heat Fluxes ◽  
Surface Energy Budget ◽  
Turbulent Heat ◽  
Turbulent Heat Fluxes

AbstractRising temperatures in the southern Arctic region are leading to shrub expansion and permafrost degradation. The objective of this study is to analyze the surface energy budget (SEB) of a subarctic shrub tundra site that is subject to these changes, on the east coast of Hudson Bay in eastern Canada. We focus on the turbulent heat fluxes, as they have been poorly quantified in this region. This study is based on data collected by a flux tower using the eddy covariance approach and focused on snow-free periods. Furthermore, we compare our results with those from six Fluxnet sites in the Arctic region and analyze the performance of two land surface models, SVS and ISBA, in simulating soil moisture and turbulent heat fluxes. We found that 23% of the net radiation was converted into latent heat flux at our site, 35% was used for sensible heat flux, and about 15% for ground heat flux. These results were surprising considering our site was by far the wettest site among those studied, and most of the net radiation at the other Arctic sites was consumed by the latent heat flux. We attribute this behavior to the high hydraulic conductivity of the soil (littoral and intertidal sediments), typical of what is found in the coastal regions of the eastern Canadian Arctic. Land surface models overestimated the surface water content of those soils but were able to accurately simulate the turbulent heat flux, particularly the sensible heat flux and, to a lesser extent, the latent heat flux.

scholarly journals Spiciness Anomalies in the Upper South Indian Ocean

2018 ◽  
Vol 48 (9) ◽  
pp. 2081-2101 ◽  
Author(s):  
Motoki Nagura ◽  
Shinya Kouketsu
Keyword(s):  
Indian Ocean ◽  
Southern Oscillation ◽  
Mixed Layer Depth ◽  
Surface Heat ◽  
Surface Fluxes ◽  
Sea Surface Salinity ◽  
South Indian Ocean ◽  
South Indian ◽  
Generation Region ◽  
Upper South

AbstractThis study investigates an isopycnal temperature/salinity T/S, or spiciness, anomaly in the upper south Indian Ocean for the period from 2004 to 2015 using observations and reanalyses. Spiciness anomalies at about 15°S on 24–26σθ are focused on, whose standard deviation is about 0.1 psu in salinity and 0.25°C in temperature, and they have a contribution to isobaric temperature variability comparable to thermocline heave. A plausible generation region of these anomalies is the southeastern Indian Ocean, where the 25σθ surface outcrops in southern winter, and the anticyclonic subtropical gyre advects subducted water equatorward. Unlike the Pacific and Atlantic, spiciness anomalies in the upper south Indian Ocean are not T/S changes in mode water, and meridional variations in SST and sea surface salinity in their generation region are not density compensating. It is possible that this peculiarity is owing to freshwater originating from the Indonesian Seas. The production of spiciness anomalies is estimated from surface heat and freshwater fluxes and the surface T/S relationship in the outcrop region, based on several assumptions including the dominance of surface fluxes in the surface T/S budget and effective mixed layer depth proposed by Deser et al. The result agrees well with isopycnal salinity anomalies at the outcrop line, which indicates that spiciness anomalies are generated by local surface fluxes. It is suggested that the Ningaloo Niño and El Niño–Southern Oscillation lead to interannual variability in surface heat flux in the southeastern Indian Ocean and contribute to the generation of spiciness anomalies.

The Importance of Relative Wind Speed in Estimating Air–Sea Turbulent Heat Fluxes in Bulk Formulas: Examples in the Bohai Sea

2020 ◽  
Vol 37 (4) ◽  
pp. 589-603 ◽  
Author(s):  
Xiangzhou Song
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Wind Speed ◽  
Bohai Sea ◽  
Heat Fluxes ◽  
Turbulent Heat ◽  
Surface Currents ◽  
The Bohai Sea ◽  
Turbulent Heat Fluxes ◽  
Relative Wind

AbstractSea surface currents are commonly neglected when estimating the air–sea turbulent heat fluxes in bulk formulas. Using buoy observations in the Bohai Sea, this paper investigated the effects of near-coast multiscale currents on the quantification of turbulent heat fluxes, namely, latent heat flux (LH) and sensible heat flux (SH). The maximum current reached 1 m s−1 in magnitude, and a steady northeastward current of 0.16 m s−1 appeared in the southern Bohai Strait. The predominant tidal signal was the semidiurnal current, followed by diurnal components. The mean absolute surface wind was from the northeast with a speed of approximately 3 m s−1. The surface winds at a height of 11 m were dominated by the East Asian monsoon. As a result of upwind flow, the monthly mean differences in LH and SH between the estimates with and without surface currents ranged from 1 to 2 W m−2 in July (stable boundary layer) and November (unstable boundary layer). The hourly differences were on average 10 W m−2 and ranged from 0 to 24 W m−2 due to changes in the relative wind speed by high-frequency rotating surface tidal currents. The diurnal variability in LH/SH was demonstrated under stable and unstable boundary conditions. Observations provided an accurate benchmark for flux comparisons. The newly updated atmospheric reanalysis products MERRA-2 and ERA5 were superior to the 1° OAFlux data at this buoy location. However, future efforts in heat flux computation are still needed to, for example, consider surface currents and resolve diurnal variations.

scholarly journals Assessing Surface Heat Flux Products with In Situ Observations over the Australian Sector of the Southern Ocean

2019 ◽  
Vol 36 (9) ◽  
pp. 1849-1861
Author(s):  
Vidhi Bharti ◽  
Eric Schulz ◽  
Christopher W. Fairall ◽  
Byron W. Blomquist ◽  
Yi Huang ◽  
...  
Keyword(s):  
Heat Flux ◽  
Southern Ocean ◽  
Sensible Heat Flux ◽  
Surface Heat ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Atmospheric Composition ◽  
Systematic Bias ◽  
Positive Bias

Given the large uncertainties in surface heat fluxes over the Southern Ocean, an assessment of fluxes obtained by European Centre for Medium-Range Weather Forecasts interim reanalysis (ERA-Interim) product, the Australian Integrated Marine Observing System (IMOS) routine observations, and the Objectively Analyzed Air–Sea Heat Fluxes (OAFlux) project hybrid dataset is performed. The surface fluxes are calculated using the COARE 3.5 bulk algorithm with in situ data obtained from the NOAA Physical Sciences Division flux system during the Clouds, Aerosols, Precipitation, Radiation, and Atmospheric Composition over the Southern Ocean (CAPRICORN) experiment on board the R/V Investigator during a voyage (March–April 2016) in the Australian sector of the Southern Ocean (43°–53°S). ERA-Interim and OAFlux data are further compared with the Southern Ocean Flux Station (SOFS) air–sea flux moored surface float deployed for a year (March 2015–April 2016) at ~46.7°S, 142°E. The results indicate that ERA-Interim (3 hourly at 0.25°) and OAFlux (daily at 1°) estimate sensible heat flux H s accurately to within ±5 W m−2 and latent heat flux H l to within ±10 W m−2. ERA-Interim gives a positive bias in H s at low latitudes (<47°S) and in H l at high latitudes (>47°S), and OAFlux displays consistently positive bias in H l at all latitudes. No systematic bias with respect to wind or rain conditions was observed. Although some differences in the bulk flux algorithms are noted, these biases can be largely attributed to the uncertainties in the observations used to derive the flux products.

scholarly journals Spatiotemporal Characteristics of the Dominant Modes of Surface Air Temperature Interannual Variations over South China during the Spring-to-Summer Transition

Atmosphere ◽  
2019 ◽  
Vol 10 (2) ◽  
pp. 65
Author(s):  
Fen Wang ◽  
Yaokun Li ◽  
Jianping Li
Keyword(s):  
Heat Flux ◽  
Air Temperature ◽  
South China ◽  
Surface Heat Flux ◽  
Surface Air Temperature ◽  
Surface Heat ◽  
Shortwave Radiation ◽  
Northerly Wind ◽  
The North ◽  
Land Surfaces

The surface air temperature (SAT) interannual variability during the spring-to-summer transition over South China (SC) has been decomposed into two dominant modes by applying empirical orthogonal function (EOF) analysis. The first EOF mode (EOF1) is characterized by homogenous SAT anomalies over SC, whereas the second EOF mode (EOF2) features a dipole SAT anomaly pattern with opposite anomalies south and north of the Yangtze River. A regression analysis of surface heat flux and advection anomalies on the normalized principle component time series corresponding to EOF1 suggests that surface heat flux anomalies can explain SAT anomalies mainly by modulating cloud-shortwave radiation. Negative cloud anomalies result in positive downward shortwave radiation anomalies through the positive shortwave cloud radiation effect, which favor warm SAT anomalies over most of SC. For EOF2, the distribution of advection anomalies resembles the north–south dipole pattern of SAT anomalies. This suggests that wind-induced advection plays an important role in the SAT anomalies of EOF2. Negative SAT anomalies are favored by cold advection from northerly wind anomalies over land surfaces in high-latitude regions. Positive SAT anomalies are induced by warm advection from southerly wind anomalies over the ocean in low-latitude regions.

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