Justin Finkel

Bio: Justin Finkel is an academic researcher from University of Chicago. The author has contributed to research in topics: Rare events & Sudden stratospheric warming. The author has an hindex of 5, co-authored 14 publications receiving 74 citations. Previous affiliations of Justin Finkel include Washington University in St. Louis.

Path properties of atmospheric transitions: Illustration with a low-order sudden stratospheric warming model

Abstract: Many rare weather events, including hurricanes, droughts, and floods, dramatically impact human life. To accurately forecast these events and characterize their climatology requires special...

Learning forecasts of rare stratospheric transitions from short simulations

Abstract: Nonlinear atmospheric dynamics produce rare events that are hard to predict and attribute due to many interacting degrees of freedom. Sudden stratospheric warming event is a model example. Approximately once every other year, the winter polar vortex in the boreal stratosphere rapidly breaks down, inducing a shift in midlatitude surface weather patterns persisting for up to 2-3 months. In principle, lengthy numerical simulations can be used to predict and understand these rare transitions. For complex models, however, the cost of the direct numerical simulation approach is often prohibitive. We describe an alternative approach which only requires relatively short-duration computer simulations of the system. The methodology is illustrated by applying it to a prototype model of an SSW event developed by Holton and Mass (1976) and driven with stochastic forcing. While highly idealized, the model captures the essential nonlinear dynamics of SSWs and exhibits the key forecasting challenge: the dramatic separation in timescales between the dynamics of a single event and the return time between successive events. We compute optimal forecasts of sudden warming events and quantify the limits of predictability. Statistical analysis relates these optimal forecasts to a small number of interpretable physical variables. Remarkably, we are able to estimate these quantities using a data set of simulations much shorter than the timescale of the warming event. This methodology is designed to take full advantage of the high-dimensional data from models and observations, and can be employed to find detailed predictors of many complex rare events arising in climate dynamics.

Changing world extreme temperature statistics

Abstract: We use the Global Historical Climatology Network – daily database to calculate a nonparametric statistic that describes the rate at which all-time daily high- and low-temperature records have been set in nine geographic regions (continents or major portions of continents) during periods mostly from the mid-20th century to the present. This statistic was defined in our earlier work on temperature records in the 48 contiguous United States. In contrast to this earlier work, we find that in every region except North America all-time high records were set at a rate significantly (at least 3σ) higher than in the null hypothesis of a stationary climate. Except in Antarctica, all-time low records were set at a rate significantly lower than in the null hypothesis. In Europe, North Africa and North Asia the rate of setting new all-time highs increased suddenly in the 1990s, suggesting a change in regional climate regime; in most other regions there was a steadier increase.

Decreasing US aridity in a warming climate

Abstract: The mean North American and world climates have warmed since the 19th century following the anthropogenic emission of large quantities of greenhouse gases. It has been suggested that this warming may increase the frequency or severity of droughts. We define a quantitative and objective aridity index that describes the precipitation forcing function of drought. Using the extensive historical database of precipitation records, we evaluate changes in the aridity in the 48 contiguous United States. The area-averaged mean fractional rate of change of aridity of 1218 sites in the period 1893–2013 was (−6.6 ± 0.4) × 10− 4 per year; the 48 contiguous United States became less arid. The rate of decrease of aridity was roughly consistent with expectations from the Clausius–Clapeyron relation and the rate of warming. The fractional rate of change of aridity was nearly uncorrelated with the aridity itself, but there were regional differences: many Western and coastal Southeastern sites showed increasing aridity, but regions of rapidly decreasing aridity were found in a band 85∘–100∘W and the Northeast.

Heat Waves, the New Normal: Summertime Temperature Extremes Will Impact Animals, Ecosystems, and Human Communities

Abstract: A consequence of climate change is the increased frequency and severity of extreme heat waves. This is occurring now as most of the warmest summers and most intense heat waves ever recorded have been during the past decade. In this review, I describe the ways in which animals and human populations are likely to respond to increased extreme heat, suggest how to study those responses, and reflect on the importance of those studies for countering the devastating impacts of climate change.

The stratigraphy and evolution of lower Mount Sharp from spectral, morphological, and thermophysical orbital data sets

Abstract: We have developed a refined geologic map and stratigraphy for lower Mt. Sharp using coordinated analyses of new spectral, thermophysical, and morphologic orbital data products. The Mt. Sharp group consists of seven relatively planar units delineated by differences in texture, mineralogy, and thermophysical properties. These units are (1-3) three spatially adjacent units in the Murray formation which contain a variety of secondary phases and are distinguishable by thermal inertia and albedo differences, (4) a phyllosilicate-bearing unit, (5) a hematite-capped ridge unit, (6) a unit associated with material having a strongly sloped spectral signature at visible-near infrared wavelengths, and (7) a layered sulfate unit. The Siccar Point group consists of the Stimson formation and two additional units that unconformably overlie the Mt. Sharp group. All Siccar Point group units are distinguished by higher thermal inertia values and record a period of substantial deposition and exhumation that followed the deposition and exhumation of the Mt. Sharp group. Several spatially extensive silica deposits associated with veins and fractures show late stage silica enrichment within lower Mt. Sharp was pervasive. At least two laterally extensive hematitic deposits are present at different stratigraphic intervals, and both are geometrically conformable with lower Mt. Sharp strata. The occurrence of hematite at multiple stratigraphic horizons suggests redox interfaces were widespread in space and/or in time, and future measurements by the Mars Science Laboratory Curiosity rover will provide further insights into the depositional settings of these and other mineral phases.

The distribution of ammonia on Jupiter from a preliminary inversion of Juno Microwave Radiometer data

Abstract: The Juno microwave radiometer measured the thermal emission from Jupiter's atmosphere from the cloud tops at about 1 bar to as deep as a hundred bars of pressure during its first flyby over Jupiter (PJ1) The nadir brightness temperatures show that the Equatorial Zone is likely to be an ideal adiabat, which allows a determination of the deep ammonia abundance in the range 362^(+33)_(-33) ppm The combination of Markov chain Monte Carlo method and Tikhonov regularization is studied to invert Jupiter's global ammonia distribution assuming a prescribed temperature profile The result shows (1) that ammonia is depleted globally down to 50–60 bars except within a few degrees of the equator, (2) the North Equatorial Belt is more depleted in ammonia than elsewhere, and (3) the ammonia concentration shows a slight inversion starting from about 7 bars to 2 bars These results are robust regardless of the choice of water abundance

Drought under Global Warming: A Review

Abstract: This article reviews recent literature on drought of the last millennium, followed by an update on global aridity changes from 1950 to 2008. Projected future aridity is presented based on recent studies and our analysis of model simulations. Dry periods lasting for years to decades have occurred many times during the last millennium over, for example, North America, West Africa, and East Asia. These droughts were likely triggered by anomalous tropical sea surface temperatures (SSTs), with La Ni˜ na-like SST anomalies leading to drought in North America, and El-Ni˜ no-like SSTs causing drought in East China. Over Africa, the southward shift of the warmest SSTs in the Atlantic and warming in the Indian Ocean are responsible for the recent Sahel droughts. Local feedbacks may enhance and prolong drought. Global aridity has increased substantially since the 1970s due to recent drying over Africa, southern Europe, East and South Asia, and eastern Australia. Although El Ni˜ no-Southern Oscillation (ENSO), tropical Atlantic SSTs, and Asian monsoons have played a large role in the recent drying, recent warming has increased atmospheric moisture demand and likely altered atmospheric circulation patterns, both contributing to the drying. Climate models project increased aridity in the 21 st century over most of Africa, southern Europe and the Middle East, most of the Americas, Australia, and Southeast Asia. Regions like the United States have avoided prolonged droughts during the last 50 years due to natural climate variations, but might see persistent droughts in the next 20–50 years. Future efforts to predict drought will depend on models’ ability to predict tropical SSTs. 2010 JohnWiley &Sons,Ltd.WIREs Clim Change2010 DOI:10.1002/wcc.81

Compositional variations in sands of the Bagnold Dunes, Gale crater, Mars, from visible‐shortwave infrared spectroscopy and comparison with ground truth from the Curiosity rover

Abstract: During its ascent up Mount Sharp, the Mars Science Laboratory Curiosity rover traversed the Bagnold Dune Field. We model sand modal mineralogy and grain size at four locations near the rover traverse, using orbital shortwave infrared single-scattering albedo spectra and a Markov chain Monte Carlo implementation of Hapke's radiative transfer theory to fully constrain uncertainties and permitted solutions. These predictions, evaluated against in situ measurements at one site from the Curiosity rover, show that X-ray diffraction-measured mineralogy of the basaltic sands is within the 95% confidence interval of model predictions. However, predictions are relatively insensitive to grain size and are nonunique, especially when modeling the composition of minerals with solid solutions. We find an overall basaltic mineralogy and show subtle spatial variations in composition in and around the Bagnold Dunes, consistent with a mafic enrichment of sands with cumulative aeolian-transport distance by sorting of olivine, pyroxene, and plagioclase grains. Furthermore, the large variations in Fe and Mg abundances (~20 wt %) at the Bagnold Dunes suggest that compositional variability may be enhanced by local mixing of well-sorted sand with proximal sand sources. Our estimates demonstrate a method for orbital quantification of composition with rigorous uncertainty determination and provide key constraints for interpreting in situ measurements of compositional variability within Martian aeolian sandstones.