Time filter

Source Type

Goncharenko L.P.,Massachusetts Institute of Technology | Hsu V.W.,University of Colorado at Boulder | Brum C.G.M.,National Astronomy and Ionosphere Center | Zhang S.-R.,Massachusetts Institute of Technology | Fentzke J.T.,Laurel University
Journal of Geophysical Research: Space Physics | Year: 2013

This paper presents a case study of the day-to-day variability in the midlatitude upper atmospheric ion temperature (∼200-400 km) with a focus on variability resulting from meteorological forcing. The data are obtained by the Millstone Hill incoherent scatter radar (42.6°N, 288.5°E) on 18-31 January 2010, in coincidence with a major sudden stratospheric warming. We elucidate oscillations in ion temperature with both tidal periods (∼8 h and ∼12 h) and non-tidal periods (>24 h) by analyzing residuals between the observed temperatures and those expected from an empirical model. We present the spatial-temporal development of periodicities in ion temperature and discuss to what degree these periodicities might be related to the sudden stratospheric warming event. The spectral location and temporal evolution of periodicities with ∼9.9-12.9 h and ∼6.2-7.9 h suggest that they are related to the semidiurnal (12 h) and terdiurnal (8 h) tides that are enhanced during the sudden stratospheric warming. Periodicities with ∼3-4 d and ∼10-13 d are likely related to Rossby waves with 4 d and 10 d periods, while the strong periodicity observed at 16-17 h could result from the nonlinear interaction of the quasi 2 d wave with the semidiurnal tide. As planetary waves are not expected to propagate to altitudes of ∼200-250 km, these experimental results raise questions about the potential mechanisms of coupling between the lower and upper atmosphere. © 2012. American Geophysical Union. All Rights Reserved.

Nuding D.L.,University of Colorado at Boulder | Rivera-Valentin E.G.,National Astronomy and Ionosphere Center | Davis R.D.,University of Colorado at Boulder | Gough R.V.,University of Colorado at Boulder | And 2 more authors.
Icarus | Year: 2014

Calcium perchlorate (Ca(ClO4)2) is a highly deliquescent salt that may exist on the surface of present-day Mars; however, its water uptake properties have not been well characterized at temperatures and relative humidity conditions relevant to Mars. Here, we quantify the deliquescent relative humidity (DRH) and efflorescent relative humidity (ERH) of Ca(ClO4)2 as a function of temperature (223-273K) to elucidate its behavior on the surface of Mars. A Raman microscope equipped with an environmental cell was used to simulate Mars relevant temperature and relative humidity conditions and monitor deliquescence (solid to aqueous) and efflorescence (aqueous to solid) phase transitions of Ca(ClO4)2. Deliquescence and efflorescence were monitored visually using optical images and spectroscopically using Raman microscopy. We find that there is a wide range of deliquescence RH values between 5% and 55% RH. This range is due to the formation of hydrates in different temperatures regimes, with the higher DRH values occurring at the lowest temperatures. Experimental deliquescence results were compared to a thermodynamic model for three hydration states of Ca(ClO4)2. The model predicts that the higher hydration states deliquesce at a higher RH than the lower hydration states. Calcium perchlorate was found to supersaturate, with lower ERH values than DRH values. The ERH results were less dependent on temperature with an average 15±4%, but values as low as 3±2% were measured at 273K. Levitation experiments were performed on single particles of Ca(ClO4)2 and Mg(ClO4)2 at 298K. While efflorescence was observed around 15% RH for Mg(ClO4)2, the efflorescence of Ca(ClO4)2 was not observed, even when exposed to 1% RH at 298K. Additionally, a 17-h experiment was conducted to simulate a martian subsurface diurnal cycle. This demonstrated Ca(ClO4)2 aqueous solutions can persist without efflorescing for the majority of a martian sol, up to 17h under Mars temperature heating rates and RH conditions. We find that Ca(ClO4)2 aqueous solutions could persist for most of the martian sol under present-day conditions. The aqueous phase stability and metastability quantified for Ca(ClO4)2 under Mars relevant temperature and relative humidity conditions has important implications for the water cycle and the stability of liquid water on present day Mars. © 2014 Elsevier Inc.

Harmon J.K.,National Astronomy and Ionosphere Center | Slade M.A.,Jet Propulsion Laboratory | Rice M.S.,Cornell University
Icarus | Year: 2011

We present an updated survey of Mercury's putative polar ice deposits, based on high-resolution (1.5-km) imaging with the upgraded Arecibo S-band radar during 1999-2005. The north pole has now been imaged over a full range of longitude aspects, making it possible to distinguish ice-free areas from radar-shadowed areas and thus better map the distribution of radar-bright ice. The new imagery of the south pole, though derived from only a single pair of dates in 2005, improves on the pre-upgrade Arecibo imagery and reveals many additional ice features. Some medium-size craters located within 3° of the north pole show near-complete ice coverage over their floors, central peaks, and southern interior rim walls and little or no ice on their northern rim walls, while one large (90. km) crater at 85°N shows a sharp ice-cutoff line running across its central floor. All of this is consistent with the estimated polar extent of permanent shading from direct sunlight. Some craters show ice in regions that, though permanently shaded, should be too warm to maintain unprotected surface ice owing to indirect heating by reflected and reradiated sunlight. However, the ice distribution in these craters is in good agreement with models invoking insulation by a thin dust mantle. Comparisons with Goldstone X-band radar imagery indicate a wavelength dependence that could be consistent with such a dust mantle. More than a dozen small ice features have been found at latitudes between 67° and 75° All of this low-latitude ice is probably sheltered in or under steep pole-facing crater rim walls, although, since most is located in the Mariner-unimaged hemisphere, confirmation must await imaging by the MESSENGER orbiter. These low-latitude features are concentrated toward the " cold longitudes," possibly indicating a thermal segregation effect governed by indirect heating. The radar imagery places the corrected locations of the north and south poles at 7°W, 88.35°N and 90°W, 88.7°S, respectively, on the original Mariner-based maps. © 2010 Elsevier Inc.

Harmon J.K.,National Astronomy and Ionosphere Center | Nolan M.C.,National Astronomy and Ionosphere Center | Giorgini J.D.,Jet Propulsion Laboratory | Howell E.S.,National Astronomy and Ionosphere Center
Icarus | Year: 2010

Arecibo radar imagery of Comet 8P/Tuttle reveals a 10-km-long nucleus with a highly bifurcated shape consistent with a contact binary. A separate echo component was also detected from large (>cm-size), slow-moving grains of the type expected to contribute to the Ursid meteor stream. © 2009 Elsevier Inc. All rights reserved.

This series of radar images of the asteroid 2015 TB145 were captured by the Arecibo Observatory in Puerto Rico. They show views of the so-called Halloween asteroid as it rotated during a 40-minute observation ahead of its Oct. 31, 2015 flyby of More A huge asteroid the size of the football stadium has a close encounter with Earth today (Oct. 31) and you can watch the space rock safely fly by online this Halloween. NASA scientists have dubbed asteroid a cosmic "Great Pumpkin" to celebrate the spooky holiday flyby. The newfound asteroid 2015 TB145 will buzz Earth 1:01 p.m. EDT (1701 GMT), passing by at a safe range of about 300,000 miles (480,000 kilometers), just beyond the orbit of the moon. The asteroid poses no threat of hitting Earth, but it does give astronomers a tantalizing chance to ping the space rock with radar to learn more about what it's like. Today at 1 p.m. EDT (1700 GMT), the online Slooh Community Observatory will host a free live webcast of asteroid 2015 TB145 to discuss the asteroid's flyby, the "dangers of near-Earth asteroids, the potential fallout of an asteroid this size impacting the Earth or moon and try to understand why it took so long to discover," according to a Slooh statement. You can go to Slooh.com to join and watch this broadcast live, as well as access Slooh's library of past shows. You can also watch the asteroid flyby webcast on Space.com, courtesy of Slooh. The webcast will be hosted by Slooh's Paul Cox and Slooh astronomer Bob Berman. NASA scientists have been tracking asteroid 2015 TB145 with optical telescopes and radar tools since the space rock was discovered on Oct. 10 by astronomers using the University of Hawaii's Pan-STARRS 1 telescope. [Halloween Asteroid Flyby: A Guide for Observers] "We are going to study it with optical, infrared and radar wavelengths," Marina Brozovic, a research scientist with NASA's Jet Propulsion Laboratory in Pasadena, California, said in avideo explaining the asteroid observation plan. The radar images of 2015 TB145 captured during the asteroid's closest approach should offer the best views of the space rock. "We are expecting them to be really spectacular and that they are going to show a wealth of surface features," Brozovic said. So far, observations on Friday (Oct. 30) using the Planetary Radar Group at the National Science Foundation's Arecibo Observatory in Puerto Rico have revealed that the asteroid is about 1,968.5 feet (600 meters) wide, "which is larger than expected," according to a statement from the National Astronomy and Ionosphere Center (NAIC), which runs the observatory. The asteroid also rotates once every five hours, and is hurtling through space at a speed of about 78,293 mph (126,000 km/h), according to the NAIC statement on Facebook. In addition to the Arecibo Observatory, NASA scientists will use the agency's Goldstone Solar System Radar antenna in Goldstone, California to image asteroid 2015 TB145. "The close approach of 2015 TB145 at about 1.3 times the distance of the moon's orbit, coupled with its size, suggests it will be one of the best asteroids for radar imaging we'll see for several years," JPL scientist Lance Benner, who leads NASA's asteroid radar research program, said in a statement. "We plan to test a new capability to obtain radar images with two-meter resolution for the first time and hope to see unprecedented levels of detail." The Halloween flyby will be the closest approach of an object as large as asteroid 2015 TB145 until 2027, when an asteroid even larger - the 2,600-foot (800 m) object called 1999 AN10 - will pass Earth at a range of 238,000 miles (383,023 km), or about the same distance between the Earth and moon. Copyright 2015 SPACE.com, a Purch company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

Discover hidden collaborations