Abstract. This study considersyear-to-year and decadal variations in as well as secular trendsof the sea–air CO2 flux over the 1957–2020 period,as constrained by the pCO2 measurements from the SOCATv2021 database.In a first step,we relate interannual anomalies in ocean-internal carbon sources and sinksto local interannual anomalies insea surface temperature (SST), the temporal changes in SST (dSST/dt),and squared wind speed (u2),employing a multi-linear regression.In the tropical Pacific, we find interannual variability to be dominated by dSST/dt,as arising from variations in the upwelling of colder and more carbon-rich waters into the mixed layer.In the eastern upwelling zones as well as in circumpolar bands in the high latitudes of both hemispheres,we find sensitivity to wind speed,compatible with the entrainment of carbon-rich water during wind-driven deepening of the mixed layerand wind-driven upwelling.In the Southern Ocean,the secular increase in wind speed leads to a secular increase in the carbon source into the mixed layer,with an estimated reduction in the sink trend in the range of 17 % to 42 %.In a second step,we combined the result of the multi-linear regression andan explicitly interannual pCO2-based additive correctioninto a “hybrid” estimate of the sea–air CO2 flux over the period 1957–2020.As a pCO2 mapping method,it combines (a) the ability of a regression to bridge data gaps and extrapolate intothe early decades almost void of pCO2 databased on process-related observablesand (b) the ability of an auto-regressive interpolation to follow signalseven if not represented in the chosen set of explanatory variables.The “hybrid” estimate can be applied as an ocean flux prior foratmospheric CO2 inversions covering the whole period of atmospheric CO2 data since 1957.
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The relationship between PM<sub>2.5</sub> and anticyclonic wave activity during summer over the United States
Abstract. To better understand the role of atmospheric dynamics in modulating surface concentrations of fine particulate matter (PM2.5), we relate the anticyclonic wave activity (AWA) metric and PM2.5 data from the Interagency Monitoring of Protected Visual Environment (IMPROVE) data for the period of 1988–2014 over the US. The observational results are compared with hindcast simulations over the past 2 decades using the National Center for Atmospheric Research–Community Earth System Model (NCAR CESM). We find that PM2.5 is positively correlated (up to R=0.65) with AWA changes close to the observing sites using regression analysis. The composite AWA for high-aerosol days (all daily PM2.5 above the 90th percentile) shows a similarly strong correlation between PM2.5 and AWA. The most prominent correlation occurs in the Midwestern US. Furthermore, the higher quantiles of PM2.5 levels are more sensitive to the changes in AWA. For example, we find that the averaged sensitivity of the 90th-percentile PM2.5 to changes in AWA is approximately 3 times as strong as the sensitivity of 10th-percentile PM2.5 at one site (Arendtsville, Pennsylvania; 39.92∘ N, 77.31∘ W). The higher values of the 90th percentile compared to the 50th percentile in quantile regression slopes are most prominent over the northeastern US. In addition, future changes in US PM2.5 based only on changes in climate are estimated to increase PM2.5 concentrations due to increased AWA in summer over areas where PM2.5 variations are dominated by meteorological changes, especially over the western US. Changes between current and future climates in AWA can explain up to 75 % of PM2.5 variability using a linear regression model. Our analysis indicates that higher PM2.5 concentrations occur when a positive AWA anomaly is prominent, which could be critical for understanding how pollutants respond to changing atmospheric circulation as well as for developing robust pollution projections.
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- Award ID(s):
- 1608775
- NSF-PAR ID:
- 10356647
- Date Published:
- Journal Name:
- Atmospheric Chemistry and Physics
- Volume:
- 22
- Issue:
- 11
- ISSN:
- 1680-7324
- Page Range / eLocation ID:
- 7575 to 7592
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/acp-22-7575-2022
