Research
Tropospheric transport of pollutants and tracers
Observed summertime ground-level ozone is positively correlated with air temperature. This leads to the speculation that under global warming, ozone pollution can exacerbate without more stringent emission control. We use chemical transport models to show that ozone's dependency on temperature is largely transport-driven, and can be explained by their climatological meridional gradients. This will help us understand how future ozone responds to climate change.
>>>
Zhang, X., Waugh, D. W., & Orbe, C. (2023). Dependence of northern hemisphere tropospheric transport on the midlatitude jet under abrupt CO2 increase. Journal of Geophysical Research: Atmospheres, 128, e2022JD038454. https://doi.org/10.1029/2022JD038454
Zhang, X., Waugh, D. W., Kerr, G. H., & Miller, S. M. (2022). Surface ozone-temperature relationship: The meridional gradient ratio approximation. Geophysical Research Letters, 49, e2022GL098680. https://doi.org/10.1029/2022GL098680
A schematic from Zhang et al. (2023) showing how a tracer of midlatitude surface origin responds to a poleward shift of the midlatitude jet. Enhanced eddy mixing along isentropes (gray contours) leads to less tracer in the midlatitudes and more tracer in high latitudes.
Southern Ocean Teleconnection
The Southern Ocean has shown a cooling trend in surface temperature during the satellite era. We are exploring the remote impact of this cooling outside of the Southern Ocean by setting the pace of the SST change in the Southern Ocean to the observed SST anomalies ("pacemaker" experiment), using the fully coupled CESM1 and CESM2.
>>>
Zhang, X. & Deser, C. Remote impact of observed multidecadal Southern Ocean surface temperature variability since 1949. In prep.
Kang, S. M., Yu, Y., Deser, C., Zhang, X., Kang, I., Lee, S., and Rodgers, K. B. (2023). Global impacts of recent Southern Ocean cooling. Proceedings of the National Academy of Scviences. In Press.
Zhang, X., Deser, C., & Sun, L. (2021). Is there a tropical response to recent observed southern ocean cooling? Geophysical Research Letters, 47, e2020GL091235. https://doi.org/10.1029/2020GL091235
Check out this news article that synthesizes a few different experimental designs exploring Antarctic sea ice expansion:
Blanchard-Wrigglesworth, E., I. Eisenman, S. Zhang, S. Sun, and A. Donohoe (2022), New perspectives on the enigma of expanding Antarctic sea ice, Eos, 103, https://doi.org/10.1029/2022EO220076. Published on 11 February 2022.
Arctic clouds
Clouds in the Arctic have important radiative effects on the surface climate. They are poorly represented in GCMs, but can potentially exert feedbacks with uncertain signs and magnitudes. We use a large-eddy simulation (LES) code PyCLES to model Arctic clouds in a wide range of climates. The forcings are taken from outputs of a GCM at high latitudes, so that the forcings change consistently across climates.
>>>
Zhang, X., Schneider, T., Shen, Z., Pressel, K. G., and Eisenman, I. (2022). Seasonal cycle of idealized polar clouds: large eddy simulations driven by a GCM. Journal of Advances in Modeling Earth Systems, 14, e2021MS002671. https://doi.org/10.1029/2021MS002671
Zhang, X., Schneider, T., and Kaul, C. M. (2020). Sensitivity of idealized mixed‐phase stratocumulus to climate perturbations. Quarterly Journal of the Royal Meteorological Society, 146: 3285– 3305. https://doi.org/10.1002/qj.3846
Zhang X., T. Schneider, and K. G. Pressel, Response of idealized polar clouds to climate warming, in prep.
Antarctic shelf circulation
The rapid thinning of west Antarctic ice shelves calls for better understanding of the ocean circulation on the continental shelf. We use observations acquired by elephant seals in the Southern Ocean to map out the water properties and circulation on the Bellingshausen Sea continental shelf.
>>>
Zhang, X., Thompson, A. F., Flexas, M. M., Roquet, F., and Bornemann, H. (2016). Circulation and meltwater distribution in the Bellingshausen Sea: From shelf break to coast. Geophysical Research Letters, 43, 6402– 6409. https://doi.org/10.1002/2016GL068998
Our paper was covered by The Washington Post, Klimaretter, and the MEOP consortium.
A map showing the locations of seal-acquired observations in the Bellingshausen Sea.
Snow on sea ice
We analyze snow depth on Arctic sea ice in CMIP5 models for the first time. We found significant decline in snow depth by the end of 21st century due to reduced snowfall and delayed snowfall accumulation.
The study provided scientific evidence for listing ringed seals (Phoca hispida) as threatened and endangered species.
>>>
Hezel, P. J., Zhang, X., Bitz, C. M., Kelly, B. P., and Massonnet, F. (2012). Projected decline in spring snow depth on Arctic sea ice caused by progressively later autumn open ocean freeze‐up this century. Geophysical Research Letters, 39, L17505. https://doi.org/10.1029/2012GL052794
See news coverage by UW Today, and Science Blog.