Doctor of Philosophy

dissertationThe wind-induced disruption and breakup of multiday cold-air pools are investigated using observational analyses and idealized numerical simulations. The observations are from the Persistent Cold-Air Pool (CAP) Study, which provides modern measurement of the meteorological processes affecting the duration of cold-air pools in the Salt Lake Valley of Utah. In general, the observations indicate that synoptic-scale processes control cold-air pool duration while local processes affect near-surface stratification and mixing. The most common form of CAP breakup is due to cold-air advection aloft. However, analyses reveal that some cold-air pools are destroyed or disrupted by strong winds penetrating into the valley. The resulting wind-CAP interactions are complex, involving sequential CAP displacements, internal oscillations, dynamic instabilities, and terrainflow interactions. Large Eddy Simulations of multiday cold-air pools in idealized valley topography further demonstrate that cold-air pool removal is affected by the interplay of Kelvin-Helmholtz instability and warm air advection. This dynamic instability generates breaking waves in the stratified shear flow that mix cold-air into the warmer flow aloft. Variations in the initial cold pool stratification and valley terrain affect the timescale for cold-air pool removal. Despite these variations, a basic relationship between the magnitude of the flow aloft and the strength of the underlying cold-air pool can be expressed in terms of the "CAP Froude number." This dimensionless quantity is useful for diagnosing the onset and amplification of turbulent mixing, as well as the complete removal of cold-air pools

Master of Science

thesisThis study presents an ascent-based perspective on the climatology of storm tracks across western North America for the October-April cool seasons spanning 1989-2008. Data from the ECMWF ERA-interim reanalysis are used. Synoptic scale ascent is shown to be a physically significant measure of storm location and intensity that can be accumulated over seasonal time scales to represent storm tracks. Subsynoptic scale vertical motions, such as orographic ascent, are filtered by using an alternative balance version of the omega equation. This constraint is an important consideration to estimate storm tracks in regions of complex topography. The climatological mean distribution of ascent suggests that the primary storm track occupies a sinusoidal belt across the eastern Pacific and adjacent portions of North America. The seasonal cycle in the location and intensity of storms is pronounced and consistent with synoptic experience. Interannual variations in synoptic-scale ascent are examined by principal component analysis. Meridional shifts from year-to-year of the locations of greatest ascent can be related to amplification and weakening of the climatological sinusoidal storm track. These interannual variations are found to be related to the phase of the El Niño Southern Oscillation, although the sample size of 19 seasons is a limitation for this analysis. The link between precipitation and synoptic-scale ascentis shown to be modulated by the extent to which the atmosphere is saturated

The climatology of synoptic-scale ascent over Western North America: a perspective on storm tracks

pre-printThe position and variability of storm tracks across western North America are examined during the October-April cool seasons spanning 1989-2010. The location and intensity of storms are represented by strong synoptic-scale ascent, which is diagnosed by the alternative balance omega equation applied to ECMWF Re-Analysis Interim data. This dynamically filtered method removes poorly resolved updrafts arising from subsynoptic-scale phenomena such as convection and mountain waves. The resulting vertical motions are illustrated for the case of a strong storm traversing the western United States. Summary statistics of synoptic-scale ascent are compiled over months, seasons, and the entire 21-yr period. Locations exhibiting high mean values of ascent are deemed to represent storm tracks. The climatological-mean storm track exhibits a sinusoidal shape across the eastern Pacific and western North America. The composite evolution of strong storms moving along specific segments of the storm track show regional differences (e.g., storms poleward of 508N tend to result from progressive low-amplitude troughs progressing through the mean planetary ridge, while storms over the western United States are initiated by digging troughs that temporarily suppress the mean ridge). Seasonal shifts in the storm track are pronounced and exhibit coherent regional patterns. Interannual variations in synoptic-scale ascent indicate meridional shifts in position as well as changes in the degree of amplification within the dominant sinusoidal storm track. These changes in structure are related to the phase of ENSO: El Nin˜ o (La Nin˜ a) winters favor zonal (amplified) and southern (northern) storm tracks

Schools, families, and social reproduction

Neoliberal educational discourse across the Global North is marked by an increasing homogeneity, but this masks significant socio-spatial differences in the enactment of policy. The authors focus on four facets of roll-out neoliberalism in English education policy that have expanded the function of primary schools, and redrawn the boundary between state and family responsibilities. Specifically, these are increased state support for: (1) working parenthood through provision of wraparound childcare; (2) parent-child relationships through school-led provision of parenting classes; (3) parental involvement in children’s learning; and (4) child development through schools’ fostering of extracurricular activities. The politics of policies that both enhance state responsibility for, and influence in, matters that were previously within the purview of families are complex. The collective impact of these developments has been both to reform how the work of daily and generational social reproduction is done, and to reshape the social reproduction of a classed and gendered society

Cryptic Transcription Mediates Repression of Subtelomeric Metal Homeostasis Genes

Nonsense-mediated mRNA decay (NMD) prevents the accumulation of transcripts bearing premature termination codons. Here we show that Saccharomyces cerevisiae NMD mutants accumulate 5′–extended RNAs (CD-CUTs) of many subtelomeric genes. Using the subtelomeric ZRT1 and FIT3 genes activated in response to zinc and iron deficiency, respectively, we show that transcription of these CD-CUTs mediates repression at the bona fide promoters, by preventing premature binding of RNA polymerase II in conditions of metal repletion. Expression of the main ZRT1 CD-CUT is controlled by the histone deacetylase Rpd3p, showing that histone deacetylases can regulate expression of genes through modulation of the level of CD-CUTs. Analysis of binding of the transcriptional activator Zap1p and insertion of transcriptional terminators upstream from the Zap1p binding sites show that CD-CUT transcription or accumulation also interferes with binding of the transcriptional activator Zap1p. Consistent with this model, overexpressing Zap1p or using a constitutively active version of the Aft1p transcriptional activator rescues the induction defect of ZRT1 and FIT3 in NMD mutants. These results show that cryptic upstream sense transcription resulting in unstable transcripts degraded by NMD controls repression of a large number of genes located in subtelomeric regions, and in particular of many metal homeostasis genes

State of the climate in 2018

In 2018, the dominant greenhouse gases released into Earth’s atmosphere—carbon dioxide, methane, and nitrous oxide—continued their increase. The annual global average carbon dioxide concentration at Earth’s surface was 407.4 ± 0.1 ppm, the highest in the modern instrumental record and in ice core records dating back 800 000 years. Combined, greenhouse gases and several halogenated gases contribute just over 3 W m−2 to radiative forcing and represent a nearly 43% increase since 1990. Carbon dioxide is responsible for about 65% of this radiative forcing. With a weak La Niña in early 2018 transitioning to a weak El Niño by the year’s end, the global surface (land and ocean) temperature was the fourth highest on record, with only 2015 through 2017 being warmer. Several European countries reported record high annual temperatures. There were also more high, and fewer low, temperature extremes than in nearly all of the 68-year extremes record. Madagascar recorded a record daily temperature of 40.5°C in Morondava in March, while South Korea set its record high of 41.0°C in August in Hongcheon. Nawabshah, Pakistan, recorded its highest temperature of 50.2°C, which may be a new daily world record for April. Globally, the annual lower troposphere temperature was third to seventh highest, depending on the dataset analyzed. The lower stratospheric temperature was approximately fifth lowest. The 2018 Arctic land surface temperature was 1.2°C above the 1981–2010 average, tying for third highest in the 118-year record, following 2016 and 2017. June’s Arctic snow cover extent was almost half of what it was 35 years ago. Across Greenland, however, regional summer temperatures were generally below or near average. Additionally, a satellite survey of 47 glaciers in Greenland indicated a net increase in area for the first time since records began in 1999. Increasing permafrost temperatures were reported at most observation sites in the Arctic, with the overall increase of 0.1°–0.2°C between 2017 and 2018 being comparable to the highest rate of warming ever observed in the region. On 17 March, Arctic sea ice extent marked the second smallest annual maximum in the 38-year record, larger than only 2017. The minimum extent in 2018 was reached on 19 September and again on 23 September, tying 2008 and 2010 for the sixth lowest extent on record. The 23 September date tied 1997 as the latest sea ice minimum date on record. First-year ice now dominates the ice cover, comprising 77% of the March 2018 ice pack compared to 55% during the 1980s. Because thinner, younger ice is more vulnerable to melting out in summer, this shift in sea ice age has contributed to the decreasing trend in minimum ice extent. Regionally, Bering Sea ice extent was at record lows for almost the entire 2017/18 ice season. For the Antarctic continent as a whole, 2018 was warmer than average. On the highest points of the Antarctic Plateau, the automatic weather station Relay (74°S) broke or tied six monthly temperature records throughout the year, with August breaking its record by nearly 8°C. However, cool conditions in the western Bellingshausen Sea and Amundsen Sea sector contributed to a low melt season overall for 2017/18. High SSTs contributed to low summer sea ice extent in the Ross and Weddell Seas in 2018, underpinning the second lowest Antarctic summer minimum sea ice extent on record. Despite conducive conditions for its formation, the ozone hole at its maximum extent in September was near the 2000–18 mean, likely due to an ongoing slow decline in stratospheric chlorine monoxide concentration. Across the oceans, globally averaged SST decreased slightly since the record El Niño year of 2016 but was still far above the climatological mean. On average, SST is increasing at a rate of 0.10° ± 0.01°C decade−1 since 1950. The warming appeared largest in the tropical Indian Ocean and smallest in the North Pacific. The deeper ocean continues to warm year after year. For the seventh consecutive year, global annual mean sea level became the highest in the 26-year record, rising to 81 mm above the 1993 average. As anticipated in a warming climate, the hydrological cycle over the ocean is accelerating: dry regions are becoming drier and wet regions rainier. Closer to the equator, 95 named tropical storms were observed during 2018, well above the 1981–2010 average of 82. Eleven tropical cyclones reached Saffir–Simpson scale Category 5 intensity. North Atlantic Major Hurricane Michael’s landfall intensity of 140 kt was the fourth strongest for any continental U.S. hurricane landfall in the 168-year record. Michael caused more than 30 fatalities and $25 billion (U.S. dollars) in damages. In the western North Pacific, Super Typhoon Mangkhut led to 160 fatalities and$6 billion (U.S. dollars) in damages across the Philippines, Hong Kong, Macau, mainland China, Guam, and the Northern Mariana Islands. Tropical Storm Son-Tinh was responsible for 170 fatalities in Vietnam and Laos. Nearly all the islands of Micronesia experienced at least moderate impacts from various tropical cyclones. Across land, many areas around the globe received copious precipitation, notable at different time scales. Rodrigues and Réunion Island near southern Africa each reported their third wettest year on record. In Hawaii, 1262 mm precipitation at Waipā Gardens (Kauai) on 14–15 April set a new U.S. record for 24-h precipitation. In Brazil, the city of Belo Horizonte received nearly 75 mm of rain in just 20 minutes, nearly half its monthly average. Globally, fire activity during 2018 was the lowest since the start of the record in 1997, with a combined burned area of about 500 million hectares. This reinforced the long-term downward trend in fire emissions driven by changes in land use in frequently burning savannas. However, wildfires burned 3.5 million hectares across the United States, well above the 2000–10 average of 2.7 million hectares. Combined, U.S. wildfire damages for the 2017 and 2018 wildfire seasons exceeded $40 billion (U.S. dollars)

Size dependence in chord characteristics from simulated and observed continental shallow cumulus

In this study we compare long-term Doppler and Raman lidar observations against a full month of large eddy simulations of continental shallow cumulus clouds. The goal is to evaluate if the simulations can reproduce the mean observed vertical velocity and moisture structure of cumulus clouds and their associated subcloud circulations, as well as to establish if these properties depend on the size of the cloud. We propose methods to compare continuous chords of cloud detected from Doppler and Raman lidars with equivalent chords derived from 1D and 3D model output. While the individual chords are highly variable, composites of thousands of observed and millions of simulated chords contain a clear signal. We find that the simulations underestimate cloud size and fraction but successfully reproduce the observed structure of vertical velocity and moisture perturbations. There is a clear scaling of vertical velocity and moisture anomalies below the chords with chord size, but the moisture anomalies are only 1 %-2% higher than the horizontal mean values. The differences between the observations and simulations are smaller than the difference in sampling the modeled chords in time or space. The shape of the vertical velocity and moisture anomalies from cloud chords sampled spatially from 3D model snapshots is almost perfectly symmetric. In contrast, the chords sampled temporally from the lidar observations and 1D model output have a marked asymmetry, with stronge