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The ``insolation habitable zone'' (IHZ) is the region around a star where the incoming solar radiation, combined with the forcings from the planet's atmosphere, can keep liquid water stable at the surface of the planet. Historically, studies that consider the forcings from the planet have primarily focused on the greenhouse effect of the planet's atmosphere. To remain habitable, planets at

Page 1. Eddy-driven Responses of the Hadley Cell and Tropopause Jacob Haqq-Misra Department of Meteorology, The Pennsylvania State University, University Park, PA Sukyoung Lee Department of Meteorology, The Pennsylvania State University, University Park, PA ...

Old arguments that free O(2) must have been available at Earth's surface prior to the origin of photosynthesis have been revived by a new study that shows that aerobic respiration can occur at dissolved oxygen concentrations much lower than had previously been thought, perhaps as low as 0.05 nM, which corresponds to a partial pressure for O(2) of about 4 × 10(-8) bar. We used numerical models to study whether such O(2) concentrations might have been provided by atmospheric photochemistry. Results show that disproportionation of H(2)O(2) near the surface might have yielded enough O(2) to satisfy this constraint. Alternatively, poleward transport of O(2) from the equatorial stratosphere into the polar night region, followed by downward transport in the polar vortex, may have brought O(2) directly to the surface. Thus, our calculations indicate that this "early respiration" hypothesis might be physically reasonable.

ABSTRACT Context. The presence of liquid water on the surface of early Mars and Earth is difficult to reconcile with the reduced solar luminosity at 3.8 Ga. and before, which would have imposed mean temperatures below freezing all over both planets. For the case of Earth, it has been recently suggested the hypothesis that less continental area and limited cloudiness during the Archaean may have reduced planetary albedo and thereby increased surface warming by sunlight. Aims: Here we analyze whether this novel solution explaining warming conditions on the early Earth could be applied to early Mars. Methods: We use an energy balance climate model in our calculations. Results: Our results show that early Mars could have been kept warm as long as there was a nearly global ocean and relatively sparse cloud coverage. This result is internally inconsistent, and also incompatible with most of the observed geological evidence. Conclusions: Reduced albedo is not a suitable solution for the faint young Sun problem in the case of early Mars. The combination of climatic and geochemical models is essential for understanding the stability of liquid water during the Noachian.

ABSTRACT Satellite-borne synthetic aperture radar (SAR) offers the potential for remotely sensing surface wind speed both over the open sea and in close proximity t o the coast. The resolution improvement,of SAR over scatterometers is of particular advantage near coasts. Thus, there is a need to verify the performance of SAR wind speed retrieval in coastal environments,adjacent to very complex terrain and subject to strong synoptic forcing. Mountainous,coasts present a challenge because,the wind,direction values required for SAR wind speed retrieval algorithms cannot be obtained from global model analyses with as much,accuracy there as over the open ocean or adjacent to gentle coasts where most previous SAR accuracy studies have been conducted. The performance,of SAR wind speed retrieval in this challenging environment,is tested using a seven year data set from the mountainous,coast of the Gulf of Alaska. SAR -derived wind speeds are compared with direct measurements,from three Navy Oceanographic,Meteorological Automatic Device (NOMAD) buoys. Both of the commonly used SAR wind,speed retrieval models, CMOD4 and CMOD5, were tested, as was the impact of correcting the

... 2002; Seidel and Corresponding author address: Jacob Haqq-Misra, The Penn-sylvania State University, 201 Willard Building, University Park, PA 16802. ... Page 2. Randel 2006; Son et al. 2007; Birner 2010) through the Brewer–Dobson circulation (Holton et al. 1995). ...

Phyllosilicate minerals are commonly found in marine sediments on Earth. Accordingly, the presence of an ocean in the northern lowlands of Mars during the Noachian period would be expected to lead to the presence of abundant phyllosilicates in crust of the same age. However, mineralogical data from orbiting spectrometers show that phyllosilicates are rare in the Noachian-aged crust that is exposed in impact craters in the northern lowlands. In contrast, phyllosilicate minerals are abundant in the equatorial and tropical highlands, raising doubts about the presence of an ocean. Here we use climatic and geochemical model calculations and palaeohydrological reconstructions to assess the factors that control phyllosilicate synthesis and sedimentation on early Mars. Our model results show that temperatures in an ocean confined to latitudes poleward of 30°N would have been near freezing, which would have hindered the formation of phyllosilicate minerals in the ocean basin. In addition, the presence of cold-based glaciers surrounding the ocean would have limited the delivery of phyllosilicates from the highlands to the ocean basin. We therefore suggest that the presence of a cold, Noachian ocean could explain the paucity of phyllosilicates in the Noachian-aged crust of the northern lowlands.

ABSTRACT Deliberate and unintentional radio transmissions from Earth propagate into space. These transmissions could be detected by extraterrestrial watchers over interstellar distances. This article analyzes the harm and benefits of deliberate and unintentional transmissions relevant to Earth and humanity. Comparing the magnitude of deliberate radio broadcasts intended for messaging to extraterrestrial intelligence (METI) with the background radio spectrum of Earth, we find that METI attempts to date have much lower detectability than emissions from current radio communication technologies on Earth. METI broadcasts are usually transient and several orders of magnitude less powerful than other terrestrial sources, such as astronomical and military radars, which provide the strongest detectable signals. The benefits of radio communication on Earth most probably outweigh the potential harm of detection by extraterrestrial watchers; however, the uncertainty regarding the outcome of contact with extraterrestrial beings creates difficulty in assessing whether or not to engage in long-term and large-scale METI.

In a recent editorial, Raymond Spier expresses skepticism over claims that climate change is driven by human actions and that humanity should act to avoid climate change. This paper responds to this skepticism as part of a broader review of the science and ethics of climate change. While much remains uncertain about the climate, research indicates that observed temperature increases are human-driven. Although opinions vary regarding what should be done, prominent arguments against action are based on dubious factual and ethical positions. Thus, the skepticisms in the recent editorial are unwarranted. This does not diminish the general merits of skeptical intellectual inquiry.

ABSTRACT Satellite-borne synthetic aperture radar (SAR) offers the potential for remotely sensing surface wind speed both over the open sea and in close proximity t o the coast. The resolution improvement,of SAR over scatterometers is of particular advantage near coasts. Thus, there is a need to verify the performance of SAR wind speed retrieval in coastal environments,adjacent to very complex terrain and subject to strong synoptic forcing. Mountainous,coasts present a challenge because,the wind,direction values required for SAR wind speed retrieval algorithms cannot be obtained from global model analyses with as much,accuracy there as over the open ocean or adjacent to gentle coasts where most previous SAR accuracy studies have been conducted. The performance,of SAR wind speed retrieval in this challenging environment,is tested using a seven year data set from the mountainous,coast of the Gulf of Alaska. SAR -derived wind speeds are compared with direct measurements,from three Navy Oceanographic,Meteorological Automatic Device (NOMAD) buoys. Both of the commonly used SAR wind,speed retrieval models, CMOD4 and CMOD5, were tested, as was the impact of correcting the