Welcome! You have found the home page of Brian Rose, Assistant Professor in the Department of Atmospheric and Environmental Sciences at the University at Albany.
Our group works on the fundamental dynamics of the climate system, particularly coupled atmosphere-ocean interaction. We are primarily a theoretical group and use a variety of numerical and mathematical modeling.
You can find links above to teaching, publications, code, etc. Newsworthy and noteworthy things will be posted here in our blog. Thanks for visiting!
Brian's latest paper (with colleagues Tim Cronin from MIT and Cecilia Bitz from UW) is called "Ice Caps and Ice Belts: the effects of obliquity on ice-albedo feedback". It has been accepted for publication in the Astrophysical Journal. The paper looks at the basic rules governing planetary ice extent on Earth-like exoplanets at different obliquities. Click here for a preprint of the accepted manuscript.
Obliquity is the angle of a planet's axis of rotation relative to its orbital plane. On Earth that angle is about 23.5º, and among other things, is the reason we have seasons. Something funny happens for planets at obliquity angles exceeding 55º. When you average over a whole year, the total amount of sunlight is largest at the poles and smallest at the equator.
This paper asks whether such a planet could exist with a stable, long-lived "ice belt" around the cold equator.
We take the well-known analytical "Energy Balance Model" from North (1975). This is one of the simplest models for the pole-to-equator surface temperature distribution and ice latitude on a spherical planet in the presence of poleward heat transport. To adapt this Earth-bound model to the exoplanet context, we do two things:
- Express the model equations non-dimensionally to identify the smallest set of independent planetary parameters
- Flip the model upside down for the case where obliquity exceeds 55º and the annual-average insolation gradient is reversed
We provide a complete analytical solution to the model valid for any obliquity. This solution enables some extensive analysis of the stability of ice caps and ice belts as a function of obliquity and other planetary parameters.
We find that the "ice belt" climate is easily destabilized by the ice-albedo feedback associated with albedo contrasts between the ice-free polar caps and the ice-covered equatorial regions. Consequently planets in a stable ice belt configuration should be substantially more rare than planets with Earth-like stable ice caps.
Cameron Rencurrel has successfully completed and defended his thesis for the MS (Master of Science) degree, and is the second graduate from our group! Cameron is staying to continue on to his PhD.
Cameron's thesis is entitled Understanding Climatic Adjustments to Variations in Tropical Ocean Heat Transport. It is a follow-up study to Rose and Ferreira (2013, J. Climate). The tropical oceans take up vast amounts of energy through air-sea heat fluxes, especially in the equatorial regions dominated by wind-driven upwelling of cold water. Over long time periods, this tropical heat uptake is roughly balanced by heat release from the ocean to the atmosphere in other regions closer to the poles.
Cameron has been studying how and why this energy transport by ocean currents affects the global climate. We subject an aquaplanet GCM to a large array of different spatial patterns and magnitudes of ocean heat transport, and look at how variations in the transport affect aspects of the time-mean climate. We find that an increase in poleward heat transport by the tropical ocean results in a warming of the extra-tropics, relatively little change in the tropical temperatures, moistening of the subtropical dry zones, and partial but incomplete compensation of the planetary-scale energy transport by the atmosphere. This compensation is partially carried out by changes in the tropical Hadley circulation, and is manifested in simultaneous changes in both the mass flux of the cell and its efficiency (the so-called Gross Moist Stability). These dynamical changes are strongly coupled to thermodynamic and radiative processes that govern the global warming.
These experiments provide new insight into mechanisms of past climate changes on Earth, which have been driven in part by tectonic changes in ocean basins and consequent changes in ocean circulation and heat transport.
Publications based on these results are in preparation.
Lance Rayborn has successfully completed and defended his thesis for the MS (Master of Science) degree, and is the first graduate from our group!
Lance's thesis is entitled Understanding the Dependence of Radiative Feedbacks and Clouds on the Spatial Structure of Ocean Heat Uptake. It is a follow-up study to Rose et al. (2014, GRL). Lance used a variety of analysis techniques including radiative kernels to carefully compare the response of several different climate models to specific imposed patterns of ocean heat uptake. In particular, the study aims to draw specific causal links between spatial patterns of heat uptake under transient global warming and cloud processes that shape the overall global climate sensitivity.
A publication based on these results is in preparation.
The paper is Rose and Rayborn, "The effects of ocean heat uptake on transient climate sensitivity". It deals with the phenomenon of time-dependent climate sensitivity, and explores some compelling new ideas about connections between the oceans, atmospheric radiation, and global cloud cover that determine climate sensitivity. Our paper includes substantial review as well as some interesting original results and speculations.
Climate sensitivity here means the amount of warming per unit additional energy flux into the system. When a comprehensive coupled climate model is subjected to a steady radiative forcing (such as an abrupt increase in atmospheric CO2), we typically find that the climate sensitivity increases with time as the model adjusts towards its new, warmer equilibrium state. Why is this? Are new positive feedback processes coming into play as the climate warms? Is it necessary to think about the climate system as fundamentally non-linear?
We argue for a simpler alternative view: the uptake of heat by the oceans tends to be localized to the subpolar regions, and this localized heat sink is something like 2x more effective at altering the global planetary temperature than CO2 – a result that was demonstrated in one of Brian's earlier papers. We show that an apparent increase in climate sensitivity over time is a natural consequence of the gradual waning of this high-efficacy ocean heat uptake as the climate system warms toward its new equilibrium temperature.
We also argue for a robust physical mechanism linking subpolar ocean heat uptake with changes in subtropical low cloud cover, mediated by changes in the stratification of the atmosphere. See also the recent paper by Rose and Rencurrel for more on this! Understanding the constraints how low cloud changes contribute to global warming (now and in the future) is one of the key goals of modern climate science. Our results suggest that some aspects of low cloud changes may be driven in systematic ways by patterns of heat fluxes in and out of the ocean. If this is true, it may mean that errors and uncertainties in future climate model projections may be more reducible and falsifiable than we thought.
Brian contributed to a new synthesis article on the geology and climate dynamics of Snowball Earth, just submitted to Science Advances.
The lead author is Paul F. Hoffman, the geologist who has been the leading champion of the Neoproterozoic Snowball Earth hypothesis. Dr. Hoffman has long advocated for the importance of forward modeling studies of the physical and chemical environment of a Snowball Earth event, to bring context and constraints to the interpretation of the geological record. Along the way, he has cultivated relationships with some of the best climate dynamicists and modelers in the business. This review article summarizes recent progress on understanding the most profound episodes of global environmental change in Earth history.