Global environmental effects of impact-generated aerosols: Results from a general circulation model

Cooling and darkening at Earth's surface are expected to result from the interception of sunlight by the high altitude worldwide dust cloud generated by impact of a large asteroid or comet, according to the one-dimensional radioactive-convective atmospheric model (RCM) of Pollack et al. An analogous three-dimensional general circulation model (GCM) simulation obtains the same basic result as the RCM but there are important differences in detail. In the GCM simulation the heat capacity of the oceans, not included in the RCM, substantially mitigates land surface cooling. On the other hand, the GCM's low heat capacity surface allows surface temperatures to drop much more rapidly than reported by Pollack et al. These two differences between RCM and GCM simulations were noted previously in studies of nuclear winter; GCM results for comet/asteroid winter, however, are much more severe than for nuclear winter because the assumed aerosol amount is large enough to intercept all sunlight falling on Earth. In the simulation the global average of land surface temperature drops to the freezing point in just 4.5 days, one-tenth the time required in the Pollack et al. simulation. In addition to the standard case of Pollack et al., which represents the collision of a 10-km diameter asteroid with Earth, additional scenarios are considered ranging from the statistically more frequent impacts of smaller asteroids to the collision of Halley's comet with Earth. In the latter case the kinetic energy of impact is extremely large due to the head-on collision resulting from Halley's retrograde orbit

Impact of cloud-borne aerosol representation on aerosol direct and indirect effects

International audienceAerosol particles attached to cloud droplets are much more likely to be removed from the atmosphere and are much less efficient at scattering sunlight than if unattached. Models used to estimate direct and indirect effects of aerosols employ a variety of representations of such cloud-borne particles. Here we use a global aerosol model with a relatively complete treatment of cloud-borne particles to estimate the sensitivity of simulated aerosol, cloud and radiation fields to various approximations to the representation of cloud-borne particles. We find that neglecting transport of cloud-borne particles introduces little error, but that diagnosing cloud-borne particles produces global mean biases of 20% and local errors of up to 40% for aerosol, droplet number, and direct and indirect radiative forcing. Aerosol number, aerosol optical depth and droplet number are significantly underestimated in regions and seasons where and when wet removal is primarily by stratiform rather than convective clouds (polar regions during winter), but direct and indirect effects are less biased because of the limited sunlight there and then. A treatment that predicts the total mass concentration of cloud-borne particles for each mode yields smaller errors and runs 20% faster than the complete treatment. The errors are much smaller than current estimates of uncertainty in direct and indirect effects of aerosols, which suggests that the treatment of cloud-borne aerosol is not a significant source of uncertainty in estimates of direct and indirect effects

Nihilism in Mulk Raj Anand’s Untouchable and U. R. Ananthamurthy’s Samskara: A Rite for a Dead Man

Untouchable (1935) depicts the pain of its protagonist, Bakha in a single day incident. Bakha is born to an untouchable, who are known for their manual scavenging work. Set in Aristotelian model if ideal drama, the plot follows unities. Bakha is son Lakha who is happy to be called as jemadar or manual scavenger (Anand 4). Most of the story revolves around the problems Bakha faces. Bakha is not the product of old generation but is rather rational and does not accept his present situation. The story unfolds and we see numerous incidents in which Bakha is maltreated. Many a times despair and depression grips his mind, but his resilient spirit results in the change of attitude and eventually he tries to explore the new arena, ironically again to get disheartened. The depiction of Bakha, elaborates the exploitative practices that caste Hindu poses, in which the untouchable acquire lowest position in the society. Bakha tries to find solution of his problems in religion but all in vain. The only reason he works for “to him work was a sort of intoxication which gave him a glowing health and plenty of easy sleep” (10)

U. R. Ananthamurthy’s Samskar: An Insight to Prostitution in India

In the ancient times the structure under which the institution of prostitution worked was entirely different from that of the present age. While in the ancient times we find more dignified and secular attitude and even well to do prostitutes who sometimes received special attention of the kings saw much degradation in the later years. These Indian prostitutes can be compared to that of the higher class hetaira of Greece who was known for their different calibres. They were well versed in different abilities and profession to attract the men of position. In the earlier days men of position were known to spend much of their time in the company of such women. They were trained in not less than “the sixty-four arts.” The list includes the detail regarding the number of works that is expected out of profession. It deals with over all development of both mind and physique

Unstable radiative-dynamical interactions

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1988.Includes bibliographical references.by Steven John Ghan.Sc.D

Cloud Condensation Nuclei Profile Value-Added Product

The cloud condensation nuclei (CCN) concentration at cloud base is the most relevant measure of the aerosol that influences droplet formation in clouds. Since the CCN concentration depends on supersaturation, a more general measure of the CCN concentration is the CCN spectrum (values at multiple supersaturations). The CCN spectrum is now measured at the surface at several fixed ARM sites and by the ARM Mobile Facility (AMF), but is not measured at the cloud base. Rather than rely on expensive aircraft measurements for all studies of aerosol effects on clouds, a way to project CCN measurements at the surface to cloud base is needed. Remote sensing of aerosol extinction provides information about the vertical profile of the aerosol, but cannot be directly related to the CCN concentration because the aerosol extinction is strongly influenced by humidification, particularly near cloud base. Ghan and Collins (2004) and Ghan et al. (2006) propose a method to remove the influence of humidification from the extinction profiles and tie the “dry extinction” retrieval to the surface CCN concentration, thus estimating the CCN profile. This methodology has been implemented as the CCN Profile (CCNPROF) value-added product (VAP)

Indirect radiative forcing by ion-mediated nucleation of aerosol

A clear understanding of particle formation mechanisms is critical for assessing aerosol indirect radiative forcing and associated climate feedback processes. Recent studies reveal the importance of ion-mediated nucleation (IMN) in generating new particles and cloud condensation nuclei (CCN) in the atmosphere. Here we implement the IMN scheme into the Community Atmosphere Model version 5 (CAM5). Our simulations show that, compared to globally averaged results based on H<sub>2</sub>SO<sub>4</sub>-H<sub>2</sub>O binary homogeneous nucleation (BHN), the presence of ionization (i.e., IMN) halves H<sub>2</sub>SO<sub>4</sub> column burden, but increases the column integrated nucleation rate by around one order of magnitude, total particle number burden by a factor of ~3, CCN burden by ~10% (at 0.2% supersaturation) to 65% (at 1.0% supersaturation), and cloud droplet number burden by ~18%. Compared to BHN, IMN increases cloud liquid water path by 7.5%, decreases precipitation by 1.1%, and increases total cloud cover by 1.9%. This leads to an increase of total shortwave cloud radiative forcing (SWCF) by 3.67 W m<sup>−2</sup> (more negative) and longwave cloud forcing by 1.78 W m<sup>−2</sup> (more positive), with large spatial variations. The effect of ionization on SWCF derived from this study (3.67 W m<sup>−2</sup>) is a factor of ~3 higher that of a previous study (1.15 W m<sup>−2</sup>) based on a different ion nucleation scheme and climate model. Based on the present CAM5 simulation, the 5-yr mean impacts of solar cycle induced changes in ionization rates on CCN and cloud forcing are small (~−0.02 W m<sup>−2</sup>) but have larger inter-annual (from −0.18 to 0.17 W m<sup>−2</sup>) and spatial variations

Modelling the synoptic scale relationship between eddy heat flux and the meridional temperature gradient

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Meteorology and Physical Oceanography, 1981.Microfiche copy available in Archives and Science.Bibliography: leaves 63-65.by Steven John Ghan.M.S

Effect Of Spray-dried Ethanolic Extract of Andrographis Paniculata (Burm. F.) Nees On Streptozotocin-induced Diabetic Female Rats.

The objective of this study was to evaluate the effect of commercially prepared spray-dried ethanolic extract ol Andrographis paniculafa (AP) on streptozotocin (STZ)-induced diabetic female rats. METHODOLOGY: Rats with regular estrous cycle (EC) prior to STZ induction were randomly divided into five groups. The normal (nondiabetic) and diabetic controlgroups were given vehicle [0.2 ml of 2o/o carboxyl methyl cellulose (CMC) by gavagingl daily for 6 weeks. Other diabetic groups were treated with 50, 100 and 200 mg/kg/day of AP extracts respectively. The rats' body weight (BW), fasting blood glucose and insulin level were measured; and daily, EC evaluation was perfo;.ry1e.d1 throughout the 6-week study period. At the end.olthe experiment, rats were sacrificed and their P4fprpases were removed for histological examination."RESU LTS':, The survival rates and estrous cycle,'$f''AP-treatbd diabetic animals were found to be improved compared to nontreated animals