Ph.D. Thesis Defense Announcement

Advances in Understanding and Modeling of Heat Transfer across Earth’s Surfaces

By

Weiqiang Jing

Advisor:

Dr. Jingfeng Wang

Committee Members: Dr. Jian Luo (CEE), Dr. Aris Georgakakos (CEE), Dr. Yi Deng (EAS), Dr. Heping Liu (Washington State University)

Date and Time: August 18, 2025. 12:00PM-2:00PM

Location: SEB 122

Zoom Meeting ID: 971 7184 1840 Passcode: 328377

Complete announcement, with abstract, is attached.

Abstract:
Heat transfer processes fundamentally control Earth's surface energy balance, governing
atmospheric circulation, hydrological cycles, and climate feedback. While numerical
models have dominated Earth system science for decades, they face limitations including
limited interpretability, inadequate description of micro-scale phenomena and high
computational costs. This thesis presents a series of advancements in understanding and
modeling heat transfer across various surfaces including land, water and snow.
A new dynamic equation of surface temperature forced by solar radiation is postulated
based on a special case of transparent medium of snow. The equation links the change
rate of surface temperature to radiation and surface heat flux. Solar radiation term is
explicitly included in the dynamic equation for transparent media such as snow, water
and ice. The dynamic equation for transparent media reduces to the well-known forcerestore
model of soil surface temperature. The general dynamic equation of surface
temperature has been successfully validated for the case of snow over the Arctic and
Antarctica regions.
A mechanistic study is conducted on the dynamics of inverse temperature layer (ITL)
beneath water-atmosphere interface within which temperature increases in depth.
Existence of the ITL is a necessary condition of heat transfer from water into the
atmosphere to balance latent heat (evaporation), sensible heat flux and net longwave
radiation loss. Observations suggest that contrary to the thin (millimeter thick) cool-skin
on the top of ocean with negligible thermal storage, the depth of the ITL is much larger
and has substantial heat storage resulting from the absorption of solar radiation.
Therefore, understanding the behavior of the ITL is crucial for determining the available
energy for evaporation, which has become an increasingly significant driver of water loss
in many regions. Our analysis suggests that solar radiation and wind-driven surface layer
turbulence are shown to be the dominant mechanisms of the formation and diurnal cycle
of the ITL. The formation of daytime ITL requires sufficiently strong solar radiation
intensity and moderate wind-driven surface layer turbulent mixing. ITL prevails during
the night regardless of the daytime solar radiation intensity and wind speed. This study is
supported by field observations at an inland lake, provide potential new opportunities of
improving water-surface evaporation models.
A special focus is given to address the need for more accurate predictions of the
accelerated permafrost thawing as a result of Arctic warming. This is urgent as
permafrost degradation causes the decay of once-frozen organic matter and potentially
transforming the Arctic into a net source of greenhouse gases. Our study on the Stefan
problem, a prototype mathematical model for permafrost freezing and thawing, has led to
the first analytical solutions for the temperature distribution and active layer thickness
under general boundary conditions of time-varying surface temperature and heat flux.
They remove a “deadlock” in the study of freeze/thaw processes that has made
researchers to resort to numerical simulations with high computational cost. The classical
similarity solution of the Stefan problem is shown to be a special case under idealized
condition of constant surface temperature. The good performance of the proposed model
is supported by the field observations in the Arctic permafrost region covered with forest.
Lastly, two critical yet often overlooked processes in snow warming: 1) the “snow
greenhouse effect”, where maximum daytime temperature occur below the snow surface
and 2) the transition from a cold, subfreezing snowpack to an isothermal state. An
analytical model incorporating depth-varying thermal properties and volumetric solar
absorption successfully reproduces the “snow greenhouse effect”, with simulated
temperature profiles aligning well with observations. For the isothermal process, energy
balance analysis of a moving isothermal front indicates that it is driven solely by
volumetric solar heating rather than conduction. A conceptual model further shows that
stronger solar radiation intensity, deeper penetration depth, and warmer initial
temperature profile lead to faster isothermal onset. These findings are critical for
improving predictions of snowmelt timing and rates, which are especially important for
water resource planning, including storage management, irrigation scheduling, and
hydropower operations.
Collectively, these studies improve the understanding and modeling of heat transfer
across Earth's surfaces. The new models resulting from the thesis research have broad
applicability in Earth system science for addressing the environmental challenges of the
21st century.