Correcting Net Ocean-Atmosphere CO2 Fluxes for Near-surface Temperature Deviations.

2021 ◽  
Author(s):  
Andrew J. Watson ◽  
Jamie D. Shutler ◽  
Peter Landschützer ◽  
David K. Woolf ◽  
Thomas Holding ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Co2 Fluxes ◽  
Ocean Mixed Layer ◽  
Small Temperature ◽  
Temperature Deviation ◽  
Near Surface ◽  
Surface Ocean ◽  
Ocean Atmosphere ◽  
Two Temperature ◽  
Surface Observations

<p>We have recently shown the neglect of small temperature differences in the ocean mixed layer has led to substantial underestimates in the ocean sink for atmospheric CO<sub>2</sub> as calculated from surface pCO<sub>2</sub> observations, which we find should be increased by ~0.8 Pg Cyr-1 when globally integrated. Surface observations of ocean pCO<sub>2</sub> such as those in the SOCAT (Surface Ocean CO<sub>2</sub> Atlas, www.socat.info) are reported at a temperature typically  measured at several metres depth, but co-location of satellite estimates of the subskin surface temperature (at a few centimetres depth) differ from this, and are on average lower. In addition the top millimetre or so of the ocean is cooler than the underlying subskin because the ocean is a source of radiative and latent heat to the atmosphere. These two temperature deviations have subtly different effects on the air-sea flux of CO<sub>2</sub> as calculated by the gas exchange equation, but both result in an increase in the flux into the ocean and the combined effect is large. We are making available several datasets enabling calculation of these effects, including the regular provision of SOCAT data corrected to the subskin temperature, a climatology of the skin temperature deviation, and corrected ocean-atmosphere CO<sub>2</sub> flux estimates for the period since 1985.</p>

scholarly journals Spatiotemporal variability and drivers of <i>p</i>CO<sub>2</sub> and air–sea CO<sub>2</sub> fluxes in the California Current System: an eddy-resolving modeling study

2014 ◽  
Vol 11 (3) ◽  
pp. 671-690 ◽  
Author(s):  
G. Turi ◽  
Z. Lachkar ◽  
N. Gruber
Keyword(s):  
Surface Temperature ◽  
Dissolved Inorganic Carbon ◽  
Current System ◽  
California Current ◽  
Spatiotemporal Variability ◽  
Co2 Fluxes ◽  
Biological Reduction ◽  
California Current System ◽  
Surface Ocean ◽  
Source Sink

Abstract. We quantify the CO2 source/sink nature of the California Current System (CalCS) and determine the drivers and processes behind the mean and spatiotemporal variability of the partial pressure of CO2 (pCO2) in the surface ocean. To this end, we analyze eddy-resolving, climatological simulations of a coupled physical–biogeochemical oceanic model on the basis of the Regional Oceanic Modeling System (ROMS). In the annual mean, the entire CalCS within 800 km of the coast and from ∼33° N to 46° N is essentially neutral with regard to atmospheric CO2: the model simulates an integrated uptake flux of −0.9 ± 3.6 Tg C yr−1, corresponding to an average flux density of −0.05 ± 0.20 mol C m−2 yr−1. This near zero flux is a consequence of an almost complete regional compensation between (i) strong outgassing in the nearshore region (first 100 km) that brings waters with high concentrations of dissolved inorganic carbon (DIC) to the surface and (ii) and a weaker, but more widespread uptake flux in the offshore region due to an intense biological reduction of this DIC, driven by the nutrients that are upwelled together with the DIC. The air–sea CO2 fluxes vary substantially in time, both on seasonal and sub-seasonal timescales, largely driven by variations in surface ocean pCO2. Most of the variability in pCO2 is associated with the seasonal cycle, with the exception of the nearshore region, where sub-seasonal variations driven by mesoscale processes dominate. In the regions offshore of 100 km, changes in surface temperature are the main driver, while in the nearshore region, changes in surface temperature, as well as anomalies in DIC and alkalinity (Alk) owing to changes in circulation, biological productivity and air–sea CO2 fluxes dominate. The prevalence of eddy-driven variability in the nearshore 100 km leads to a complex spatiotemporal mosaic of surface ocean pCO2 and air–sea CO2 fluxes that require a substantial observational effort to determine the source/sink nature of this region reliably.

scholarly journals Spatiotemporal variability and drivers of <i>p</i>CO<sub>2</sub> and air–sea CO<sub>2</sub> fluxes in the California Current System: an eddy-resolving modeling study

2013 ◽  
Vol 10 (8) ◽  
pp. 14043-14091 ◽  
Author(s):  
G. Turi ◽  
Z. Lachkar ◽  
N. Gruber
Keyword(s):  
Surface Temperature ◽  
Flux Density ◽  
Current System ◽  
California Current ◽  
Spatiotemporal Variability ◽  
Co2 Fluxes ◽  
California Current System ◽  
Surface Ocean ◽  
Average Flux ◽  
Source Sink

Abstract. We quantify the CO2 source/sink nature of the California Current System (CalCS) and determine the drivers and processes behind the mean and spatiotemporal variability of the partial pressure of CO2 (pCO2) in the surface ocean. To this end, we analyze eddy-resolving, climatological simulations of a coupled physical-ecosystem-biogeochemical ocean model on the basis of the Regional Oceanic Modeling System (ROMS). The model-simulated pCO2 agrees very well with in situ observations over the entire domain with virtually no bias, but the model overestimates pCO2 in the nearshore 100 km, and underestimates the observed temporal variability. In the annual mean, the entire CalCS within 800 km of the coast and from ~ 33° N to 46° N is essentially neutral with regard to atmospheric CO2. The model simulates an integrated uptake flux of −0.9 Tg C yr–1, corresponding to a very small average flux density of −0.05 mol C m–2 yr–1, with an uncertainty of the order of ±0.20 mol C m–2 yr–1. This near zero flux is a consequence of an almost complete regional compensation between the strong outgassing in the nearshore region (first 100 km), with flux densities of more than 3 mol C m–2 yr–1 and a weaker, but more widespread uptake flux in the offshore region with an average flux density of −0.17 mol C m–2 yr–1. This pattern is primarily a result of the interaction between upwelling in the nearshore that brings waters with high concentrations of dissolved inorganic carbon (DIC) to the surface, and an intense biological drawdown of this DIC, driven by the nutrients that are upwelled together with the DIC. The biological drawdown occurs too slowly to prevent the escape of a substantial amount of CO2 into the atmosphere, but this is compensated by the biological generation of undersaturated conditions offshore of 100 km, permitting the CalCS to take up most of the escaped CO2. Thus, the biological pump over the entire CalCS is essentially 100% efficient, making the preformed DIC and nutrient concentrations of the upwelled waters a primary determinant of the overall source/sink nature of the CalCS. The comparison of the standard simulation with one for preindustrial conditions show that the CalCS is taking up anthropogenic CO2 at a rate of about −1 mol C m–2 yr–1, implying that the region was a small source of CO2 to the atmosphere in preindustrial times. The air–sea CO2 fluxes vary substantially in time, both on seasonal and sub-seasonal timescales, largely driven by variations in surface ocean pCO2. There are important differences among the subregions. Notably, the total variance of the fluxes in the central nearshore CalCS is roughly 4–5 times larger than elsewhere. Most of the variability in pCO2 is associated with the seasonal cycle, except in the nearshore, where sub-seasonal variations driven by mesoscale processes dominate. In the regions offshore of 100 km, changes in surface temperature are the main driver, while in the nearshore region, changes in surface temperature, as well as anomalies in DIC and alkalinity (Alk) owing to changes in circulation, biological productivity and air–sea CO2 fluxes dominate. The dominance of eddy-driven variability in the nearshore 100 km leads to a complex spatiotemporal mosaic of surface ocean pCO2 and air–sea CO2 fluxes that require a substantial observational effort to determine the source/sink nature of this region reliably.

Idealized large-eddy simulations of stratocumulus advecting over cold water. Part 1: Boundary layer decoupling

2021 ◽  
Author(s):  
Youtong Zheng ◽  
Haipeng Zhang ◽  
Daniel Rosenfeld ◽  
Seoung-Soo Lee ◽  
Tianning Su ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Surface Temperature ◽  
Cold Water ◽  
Temperature Inversion ◽  
Atmospheric Modeling ◽  
Sea Surface ◽  
Entrainment Rate ◽  
Surface Cooling ◽  
Near Surface ◽  
Large Eddy

AbstractWe explore the decoupling physics of a stratocumulus-topped boundary layer (STBL) moving over cooler water, a situation mimicking the warm air advection (WADV). We simulate an initially well-mixed STBL over a doubly periodic domain with the sea surface temperature decreasing linearly over time using the System for Atmospheric Modeling large-eddy model. Due to the surface cooling, the STBL becomes increasingly stably stratified, manifested as a near-surface temperature inversion topped by a well-mixed cloud-containing layer. Unlike the stably stratified STBL in cold air advection (CADV) that is characterized by cumulus coupling, the stratocumulus deck in the WADV is unambiguously decoupled from the sea surface, manifested as weakly negative buoyancy flux throughout the sub-cloud layer. Without the influxes of buoyancy from the surface, the convective circulation in the well-mixed cloud-containing layer is driven by cloud-top radiative cooling. In such a regime, the downdrafts propel the circulation, in contrast to that in CADV regime for which the cumulus updrafts play a more determinant role. Such a contrast in convection regime explains the difference in many aspects of the STBLs including the entrainment rate, cloud homogeneity, vertical exchanges of heat and moisture, and lifetime of the stratocumulus deck, with the last being subject to a more thorough investigation in part 2. Finally, we investigate under what conditions a secondary stratus near the surface (or fog) can form in the WADV. We found that weaker subsidence favors the formation of fog whereas a more rapid surface cooling rate doesn’t.

scholarly journals Relative Role of Turbulent and Radiative Flux on the Near-Surface Temperature in a Single-Layer Urban Canopy Model over Houston

2017 ◽  
Vol 56 (8) ◽  
pp. 2173-2187 ◽  
Author(s):  
James Brownlee ◽  
Pallav Ray ◽  
Mukul Tewari ◽  
Haochen Tan
Keyword(s):  
Heat Flux ◽  
Surface Temperature ◽  
Single Layer ◽  
Urban Canopy ◽  
Heat Fluxes ◽  
Radiative Flux ◽  
Hydrological Processes ◽  
Urban Canopy Model ◽  
Near Surface ◽  
Canopy Model

AbstractNumerical simulations without hydrological processes tend to overestimate the near-surface temperatures over urban areas. This is presumably due to underestimation of surface latent heat flux. To test this hypothesis, the existing single-layer urban canopy model (SLUCM) within the Weather Research and Forecasting Model is evaluated over Houston, Texas. Three simulations were conducted during 24–26 August 2000. The simulations include the use of the default “BULK” urban scheme, the SLUCM without hydrological processes, and the SLUCM with hydrological processes. The results show that the BULK scheme was least accurate, and it overestimated the near-surface temperatures and winds over the urban regions. In the presence of urban hydrological processes, the SLUCM underestimates these parameters. An analysis of the surface heat fluxes suggests that the error in the BULK scheme is due to a lack of moisture at the urban surface, whereas the error in the SLUCM with hydrological processes is due to increases in moisture at the urban surface. These results confirm earlier studies in which changes in near-surface temperature were primarily due to the changes in the turbulent (latent and sensible heat) fluxes in the presence of hydrological processes. The contribution from radiative flux was about one-third of that from turbulent flux. In the absence of hydrological processes, however, the results indicate that the changes in radiative flux contribute more to the near-surface temperature changes than the turbulent heat flux. The implications of these results are discussed.

scholarly journals Investigating the role of dust in ice nucleation within clouds and further effects on the regional weather system over East Asia – Part II: modification of the weather system

2017 ◽  
Author(s):  
Lin Su ◽  
Jimmy C.H. Fung
Keyword(s):  
Surface Temperature ◽  
East Asia ◽  
South China ◽  
Indirect Effects ◽  
Convective Precipitation ◽  
Wave Radiation ◽  
Direct And Indirect Effects ◽  
Weather System ◽  
Near Surface ◽  
Atmospheric Instability

Abstract. An updated version of the Weather Research and Forecast model coupled with Chemistry (WRF-Chem) was applied to quantify and discuss the full effects of dust on the meteorological field over East Asia during March and April 2012. The performances of the model in simulating the short-wave and long-wave radiation, surface temperature, and precipitation over East Asia are improved by incorporating the effects of dust in the simulations. The radiative forcing induced by the dust-enhanced cloud radiative effect is over one order of magnitude larger than that induced by the direct effect of dust. The semi-direct and indirect effects of dust result in a substantial increase in mid- to high clouds, and a significant reduction in low clouds, leading to a decrease of near-surface temperature and an increase of temperature at the mid- to upper troposphere over East Asia. The spatial redistribution of atmospheric water vapor and modification of the vertical temperature profile over East Asia lead to an inhibition of atmospheric instability over most land areas, but an enhancement of atmospheric instability over South China and the ocean, resulting in a significant inhibition of convective precipitation in areas from central to East China, and a substantial enhancement of convective precipitation over South China. Meanwhile, non-convective precipitation is also reduced significantly over East Asia, as cloud droplets are hindered from growing large enough to form rain droplets, due to the semi-direct and indirect effects of dust. The total precipitation can be reduced or increased by up to 20 % or more.

scholarly journals Global surface-ocean <i>p</i><sup>CO<sub>2</sub></sup> and sea–air CO<sub>2</sub> flux variability from an observation-driven ocean mixed-layer scheme

Ocean Science ◽  
2013 ◽  
Vol 9 (2) ◽  
pp. 193-216 ◽  
Author(s):  
C. Rödenbeck ◽  
R. F. Keeling ◽  
D. C. E. Bakker ◽  
N. Metzl ◽  
A. Olsen ◽  
...  
Keyword(s):  
Partial Pressure ◽  
Mixed Layer ◽  
Co2 Flux ◽  
Companion Paper ◽  
Diagnostic Model ◽  
Ocean Mixed Layer ◽  
Co2 Partial Pressure ◽  
Surface Ocean ◽  
Flux Variability ◽  
Global Surface

Abstract. A temporally and spatially resolved estimate of the global surface-ocean CO2 partial pressure field and the sea–air CO2 flux is presented, obtained by fitting a simple data-driven diagnostic model of ocean mixed-layer biogeochemistry to surface-ocean CO2 partial pressure data from the SOCAT v1.5 database. Results include seasonal, interannual, and short-term (daily) variations. In most regions, estimated seasonality is well constrained from the data, and compares well to the widely used monthly climatology by Takahashi et al. (2009). Comparison to independent data tentatively supports the slightly higher seasonal variations in our estimates in some areas. We also fitted the diagnostic model to atmospheric CO2 data. The results of this are less robust, but in those areas where atmospheric signals are not strongly influenced by land flux variability, their seasonality is nevertheless consistent with the results based on surface-ocean data. From a comparison with an independent seasonal climatology of surface-ocean nutrient concentration, the diagnostic model is shown to capture relevant surface-ocean biogeochemical processes reasonably well. Estimated interannual variations will be presented and discussed in a companion paper.

scholarly journals Model-dependence of the CO<sub>2</sub> threshold for melting the hard Snowball Earth

2011 ◽  
Vol 7 (1) ◽  
pp. 17-25 ◽  
Author(s):  
Y. Hu ◽  
J. Yang ◽  
F. Ding ◽  
W. R. Peltier
Keyword(s):  
Surface Temperature ◽  
Greenhouse Effect ◽  
Surface Albedo ◽  
Snowball Earth ◽  
Pressure Broadening ◽  
Near Surface ◽  
Induced Absorption ◽  
Cloud Forcing ◽  
Clear Sky ◽  
Convective Model

Abstract. One of the critical issues of the Snowball Earth hypothesis is the CO2 threshold for triggering the deglaciation. Using Community Atmospheric Model version 3.0 (CAM3), we study the problem for the CO2 threshold. Our simulations show large differences from previous results (e.g. Pierrehumbert, 2004, 2005; Le Hir et al., 2007). At 0.2 bars of CO2, the January maximum near-surface temperature is about 268 K, about 13 K higher than that in Pierrehumbert (2004, 2005), but lower than the value of 270 K for 0.1 bar of CO2 in Le Hir et al. (2007). It is found that the difference of simulation results is mainly due to model sensitivity of greenhouse effect and longwave cloud forcing to increasing CO2. At 0.2 bars of CO2, CAM3 yields 117 Wm−2 of clear-sky greenhouse effect and 32 Wm−2 of longwave cloud forcing, versus only about 77 Wm−2 and 10.5 Wm−2 in Pierrehumbert (2004, 2005), respectively. CAM3 has comparable clear-sky greenhouse effect to that in Le Hir et al. (2007), but lower longwave cloud forcing. CAM3 also produces much stronger Hadley cells than that in Pierrehumbert (2005). Effects of pressure broadening and collision-induced absorption are also studied using a radiative-convective model and CAM3. Both effects substantially increase surface temperature and thus lower the CO2 threshold. The radiative-convective model yields a CO2 threshold of about 0.21 bars with surface albedo of 0.663. Without considering the effects of pressure broadening and collision-induced absorption, CAM3 yields an approximate CO2 threshold of about 1.0 bar for surface albedo of about 0.6. However, the threshold is lowered to 0.38 bars as both effects are considered.

scholarly journals Extreme Drought Events over the Amazon Basin: The Perspective from the Reconstruction of South American Hydroclimate

Water ◽  
2018 ◽  
Vol 10 (11) ◽  
pp. 1594 ◽  
Author(s):  
Beatriz Garcia ◽  
Renata Libonati ◽  
Ana Nunes
Keyword(s):  
Surface Temperature ◽  
Extreme Events ◽  
General Circulation ◽  
Amazon Basin ◽  
General Circulation Models ◽  
Extreme Drought ◽  
Severe Drought ◽  
South American ◽  
Spatial And Temporal Patterns ◽  
Near Surface

The Amazon basin has experienced severe drought events for centuries, mainly associated with climate variability connected to tropical North Atlantic and Pacific sea surface temperature anomalous warming. Recently, these events are becoming more frequent, more intense and widespread. Because of the Amazon droughts environmental and socioeconomic impacts, there is an increased demand for understanding the characteristics of such extreme events in the region. In that regard, regional models instead of the general circulation models provide a promising strategy to generate more detailed climate information of extreme events, seeking better representation of physical processes. Due to uneven spatial distribution and gaps found in station data in tropical South America, and the need of more refined climate assessment in those regions, satellite-enhanced regional downscaling for applied studies (SRDAS) is used in the reconstruction of South American hydroclimate, with hourly to monthly outputs from January 1998. Accordingly, this research focuses on the analyses of recent extreme drought events in the years of 2005 and 2010 in the Amazon Basin, using the SRDAS monthly means of near-surface temperature and relative humidity, precipitation and vertically integrated soil moisture fields. Results from this analysis corroborate spatial and temporal patterns found in previous studies on extreme drought events in the region, displaying the distinctive features of the 2005 and 2010 drought events.

scholarly journals Near–surface air temperature and snow skin temperature comparison from CREST-SAFE station data with MODIS land surface temperature data

2015 ◽  
Vol 12 (8) ◽  
pp. 7665-7687 ◽  
Author(s):  
C. L. Pérez Díaz ◽  
T. Lakhankar ◽  
P. Romanov ◽  
J. Muñoz ◽  
R. Khanbilvardi ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Skin Temperature ◽  
Air Temperature ◽  
Land Surface Temperature ◽  
Land Surface ◽  
Hydrological Cycle ◽  
Critical Role ◽  
Surface Air Temperature ◽  
Balance Model ◽  
Near Surface

Abstract. Land Surface Temperature (LST) is a key variable (commonly studied to understand the hydrological cycle) that helps drive the energy balance and water exchange between the Earth's surface and its atmosphere. One observable constituent of much importance in the land surface water balance model is snow. Snow cover plays a critical role in the regional to global scale hydrological cycle because rain-on-snow with warm air temperatures accelerates rapid snow-melt, which is responsible for the majority of the spring floods. Accurate information on near-surface air temperature (T-air) and snow skin temperature (T-skin) helps us comprehend the energy and water balances in the Earth's hydrological cycle. T-skin is critical in estimating latent and sensible heat fluxes over snow covered areas because incoming and outgoing radiation fluxes from the snow mass and the air temperature above make it different from the average snowpack temperature. This study investigates the correlation between MODerate resolution Imaging Spectroradiometer (MODIS) LST data and observed T-air and T-skin data from NOAA-CREST-Snow Analysis and Field Experiment (CREST-SAFE) for the winters of 2013 and 2014. LST satellite validation is imperative because high-latitude regions are significantly affected by climate warming and there is a need to aid existing meteorological station networks with the spatially continuous measurements provided by satellites. Results indicate that near-surface air temperature correlates better than snow skin temperature with MODIS LST data. Additional findings show that there is a negative trend demonstrating that the air minus snow skin temperature difference is inversely proportional to cloud cover. To a lesser extent, it will be examined whether the surface properties at the site are representative for the LST properties within the instrument field of view.

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