THIRTEEN YEARS OF WEATHER STATISTICS AT SAN PEDRO MARTIR OBSERVATORY

We present weather statistics for thirteen years of data gathered with the meteorological stations at Observatorio Astronómico Nacional in the Sierra San Pedro Mártir (OAN-SPM) over the period 2007–2019. These weather stations include sensors that measure various climatological variables. The median values of the air temperature are 10.3° C and 7.0° C for daytime and nighttime, respectively. The relative humidity follows a seasonal variation with April-June being the driest months. The median values for the sustained wind speed are 11 and 14 km hr-1 for daytime and nighttime data, respectively. Preferred wind directions are SSW and North. Sustained winds are stronger at night and during December, January and February. The annual mean rain precipitation is 313 mm, most of which occurs during the summer season as afternoon thunderstorms.

Estimating local seeing at Observatorio Astronómico Nacional in San Pedro Mártir using CFD simulations of the atmospheric boundary layer

ABSTRACT We present computational fluid dynamics simulations of the atmospheric boundary layer (ABL) at the Observatorio Astronómico Nacional in the Sierra San Pedro Mártir (OAN-SPM) whose objective is to model the seeing observed at the site. We constrain the simulations using observations of the seeing, the vertical profile of the wind speed, and the vertical profile of the temperature, the first two resolved as a function of wind direction. We successfully model the seeing observed under typical wind conditions for each direction by adopting input profiles of the wind speed, the turbulent kinetic energy, and the energy dissipation. The resulting vertical profiles of the index of refraction structure constant are qualitatively similar to the mean profile derived from studies at the site.

Geomorphic signatures of the transient fluvial response to tilting

Nonuniform rock uplift in the form of tilting has been documented in convergent margins, postorogenic landscapes, and extensional provinces. Despite the prevalence of tilting, the transient fluvial response to tilting has not been quantified such that tectonic histories involving tilt can be extracted from river network forms. We used numerical landscape evolution models to characterize the transient erosional response of a river network initially at equilibrium to rapid tilting. We focus on the case of punctuated rigid-block tilting, though we explore longer-duration tilting events and nonuniform uplift that deviates from perfect rigid-block tilting such as that observed when bending an elastic plate or with more pronounced internal deformation of a fault-bounded block. Using a model river network composed of linked 1-D river longitudinal profile evolution models, we show that the transient response to a punctuated rigid-block tilting event creates a suite of characteristic forms or geomorphic signatures in mainstem and tributary profiles that collectively are distinct from those generated by other perturbations, such as a step change in the uniform rock uplift rate or a major truncation of the headwater drainage area, that push a river network away from equilibrium. These signatures include (1) a knickpoint in the mainstem that separates a downstream profile with uniform steepness (i.e., channel gradient normalized for drainage area) from an upstream profile with nonuniform steepness, with the mainstem above the knickpoint more out of equilibrium than the tributaries following forward tilting toward the outlet, versus the mainstem less out of equilibrium than the tributaries following back tilting toward the headwaters; (2) a pattern of mainstem incision below paleo-topography markers that increases linearly up to the mainstem knickpoint or vice versa following back tilting; and (3) tributary knickzones with nonuniform steepness that mirrors that of the mainstem upstream of the slope-break knickpoint. Immediately after a punctuated tilting event, knickpoints form at the mainstem outlet and each mainstem–tributary junction. Time since the cessation of rapid tilting is recorded by the mainstem knickpoint location relative to base level and by the upstream end of tributary knickzones relative to the mainstem–tributary junction. Tilt magnitude is recorded in the spatial gradient of mainstem incision depth and, in the forward tilting case, also by the spatial gradient in tributary knickzone drop height. Heterogeneous lithology can modulate the transient response to tilting and, post tilt, knickpoints can form anywhere in a stream network where more erodible rock occurs upstream of less erodible rock. With a full 2-D model, we show that stream segments flowing in the tilt direction have elevated channel gradient early in the transient response. Tilting is also reflected in network topologic changes via stream capture oriented in the direction of tilt. As an example of how these geomorphic signatures can be used in concert with each other to estimate the timing and magnitude of a tilting event, we show a sample of rivers from two field sites: the Sierra Nevada, California, USA, and the Sierra San Pedro Mártir, Baja California, Mexico, two ranges thought to have been tilted westward toward river outlets in the late Cenozoic.

Climate change and forest plagues: assessing current and future impacts of diprionid sawflies on the pine forests of north-western Mexico

The imminent threat of climate change lies in its potential to disrupt the balance of ecosystems, particularly vulnerable areas such as mountain-top remnant forests. An example of such a fragile ecosystem is the Sierra San Pedro Mártir (SSPM) National Park of Mexico’s Baja California state, where high levels of endemism can be found, and which is home to one of the country’s few populations of the emblematic Jeffrey pine (Pinus jeffreyi). Recent outbreaks of pine-feeding sawfly larvae in SSPM increase the vulnerability of this forest ecosystem, calling for immediate assessments of the severity of this threat. Here, we present a thorough study of the sawfly’s biology and distribution, carrying out molecular and morphology-based identification of the species and creating model-based predictions of the species distribution in the area. The sawfly was found to belong to an undescribed species of the genus Zadiprion (family Diprionidae) with a one-year life-cycle. The distribution of this species appears to be restricted to the SSPM national park and it will probably persist for at least another 50 years, even considering the effects of climate change.

Primer registro de bajapalos pecho canela (Sitta canadensis) en el bosque de Los Attenuatas, Baja California

El bajapalos pecho canela (Sitta canadensis) es una especie de distribución amplia en Estados Unidos y Canadá. No obstante,debido a irrupciones y vagabundeos, se ha registrado en Chihuahua, Sonora, Sinaloa, Baja California, Nuevo León y en el occidentede México (Jalisco y Colima). En Baja California existen cuatro registros: (1) Isla Guadalupe (población que se consideraextirpada desde 1995) (2), Sierra San Pedro Mártir (3), Sierra Juárez y (4) Santa Rosaliíta, los últimos dos registros son de hacemás de 20 años. Registramos por primera vez un bajapalos pecho canela macho adulto en el bosque de Los Attenuatas durantela temporada de invierno de 2015.

A coastal population of Large-blotched Ensatina Ensatina klauberi (Caudata: Plethodontidae) in Baja California, México

We found a new population of Ensatina klauberi in San Quintín volcanic field, Baja California. It represents the first coastal population of this species. This record extends the species range ca. 71 km southwest of the southernmost record of E. klauberi in the Sierra San Pedro Mártir and represents the first population discovered outside of coniferous and pine-oak woodlands.