A gravity wave (GW) model that includes influences of temperature variations and large‐scale advection on polar mesospheric cloud (PMC) brightness having variable dependence on particle radius is developed. This Complex Geometry Compressible Atmosphere Model for PMCs (CGCAM‐PMC) is described and applied here for three‐dimensional (3‐D) GW packets undergoing self‐acceleration (SA) dynamics, breaking, momentum deposition, and secondary GW (SGW) generation below and at PMC altitudes. Results reveal that GW packets exhibiting strong SA and instability dynamics can induce significant PMC advection and large‐scale transport, and cause partial or total PMC sublimation. Responses modeled include PMC signatures of GW propagation and SA dynamics, “voids” having diameters of ∼500–1,200 km, and “fronts” with horizontal extents of ∼400–800 km. A number of these features closely resemble PMC imaging by the Cloud Imaging and Particle Size (CIPS) instrument aboard the Aeronomy of Ice in the Mesosphere (AIM) satellite. Specifically, initial CGCAM‐PMC results closely approximate various CIPS images of large voids surrounded by smaller void(s) for which dynamical explanations have not been offered to date. In these cases, the GW and instabilities dynamics of the initial GW packet are responsible for formation of the large void. The smaller void(s) at the trailing edge of a large void is (are) linked to the lower‐ or higher‐altitude SGW generation and primary mean‐flow forcing. We expect an important benefit of such modeling to be the ability to infer local forcing of the mesosphere and lower thermosphere (MLT) over significant depths when CGCAM‐PMC modeling is able to reasonably replicate PMC responses.

We have utilized Solar Backscatter Ultraviolet (SBUV) instrument measurements of atmospheric radiance to create a 40-year record of polar mesospheric cloud (PMC) behavior. While this series of measurements is nearing its end, we show in this paper that Ozone Mapping and Profiling Suite (OMPS) Nadir Profiler (NP) instruments can be added to the merged SBUV PMC data record. Regression analysis of this extended record shows smaller trends in PMC ice water content (IWC) since approximately 1998, consistent with previous work. Current trends are significant at the 95% confidence level in the Northern Hemisphere but not in the Southern Hemisphere. The PMC IWC response to solar activity has decreased in the Northern Hemisphere since 1998 but has apparently increased in the Southern Hemisphere.

High spatial resolution images of polar mesospheric clouds (PMCs) from a camera array on board the Aeronomy of Ice in the Mesosphere (AIM) satellite have been obtained since 2007. The Cloud Imaging and Particle Size Experiment (CIPS) detects scattered ultraviolet (UV) radiance at a variety of scattering angles, allowing the scattering phase function to be measured for every image pixel. With well-established scattering theory, the mean particle size and ice water content (IWC) are derived. In the nominal mode of operation, approximately seven scattering angles are measured per cloud pixel. However, because of a change in the orbital geometry in 2016, a new mode of operation was implemented such that one scattering angle, or at most two, per pixel are now available. Thus particle size and IWC can no longer be derived from the standard CIPS algorithm. The Albedo-Ice Regression (AIR) method was devised to overcome this obstacle. Using data from both a microphysical model and from CIPS in its normal mode, we show that the AIR method provides sufficiently accurate average IWC so that PMC IWC can be retrieved from CIPS data into the future, even when albedo is not measured at multiple scattering angles. We also show from the model that 265 nm UV scattering is sensitive only to ice particle sizes greater than about 20–25 nm in (effective) radius and that the operational CIPS algorithm has an average error in retrieving IWC of -13±17 %.

Water-rich rocket exhaust plumes, in particular those emitted by the National Aeronautics and Space Administration Space Shuttle, have been suggested to make a significant contribution to long-term trends in polar mesospheric cloud (PMC) ice water content. We investigate this claim using the combined Solar Backscatter Ultraviolet (SBUV) PMC data record from eight separate instruments, which includes 60 Shuttle launches during PMC seasons between 1985 and 2011. No statistically significant postlaunch signal in PMC total ice is observed based on superposed epoch analysis of the SBUV record. Only a few launches show individual peaks in total ice anomaly above the seasonal background that exceed an empirical threshold, and the maximum cumulative signature from these infrequent cases is typically less than 5% of the season total in ice mass. Other non-Shuttle launches show circumstantial evidence of possible PMC effects, although supporting evidence for plume transport is not available. We conclude that space traffic effects have been a negligible component of long-term PMC behavior.

This text provides a foundation in both the theoretical and practical aspects of radiative transfer, for advanced students of atmospheric, oceanic and environmental sciences. The transfer of solar and infrared radiation through optically-thick clouds, aerosol layer, and the oceanic mixed layer is presented through the use of heuristic models of scattering and absorption, and a systematic approach to formulation and solution of the radiative transfer equation. Problems such as the transmission of ultraviolet radiation through the atmosphere and ocean, remote sensing, solar heating and infrared cooling processes, UV biological dose rates, and greenhouse warming are solved using a variety of methods. This self-contained, systematic treatment will prepare students from a range of disciplines in problems concerning the effects of solar and infrared radiation on natural systems. The hardback edition received excellent reviews.

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Polar Mesospheric Cloud (PMC) observations from the Solar Occultation for Ice Experiment (SOFIE) and the Cloud Imaging and Particle Size (CIPS) experiment are used to investigate the response of PMCs to forcing associated with the 27-day solar rotation. We quantify the PMC response in terms of sensitivity values. Analysis of PMC data from 14 seasons indicate a large seasonal variability in sensitivity with both correlation and anti-correlation between PMC properties and Lyman-alpha irradiance for individual seasons. However, a superposed epoch analysis reveals the expected anti-correlation between variations in solar Lyman-alpha and variations in PMC ice water content, albedo, and frequency of occurrence. The PMC height is found to significantly correlate with 27-day variations in solar Lyman-alpha in the Southern Hemisphere (SH), but not in the Northern hemisphere (NH). Depending on instrument and property, the time lag between variations in PMC properties and solar Lyman-alpha ranges from 0 to 3 days in the NH and from 6 to 7 days in the SH. These hemispheric differences in PMC height and time lag are not understood, but it is speculated that they result from dynamical forcing that is controlled by the 27-day solar cycle.

Two problems in atmospheric and environmental science have received much attention: the occurrence of widespread ozone depletion and global warming. Ozone depletion has been related directly to the release of man-made trace gases, notably chlorofluorocarbons used in the refrigeration industry and as “propellants” in spray cans. Since ozone provides an effective shield against damaging ultraviolet radiation from the Sun, there is indeed good reason to be concerned, because a thinning of the ozone layer has serious biological ramifications. The most harmful ultraviolet (UV) radiation reaching the Earth's surface, commonly referred as UV-B radiation, lies in the wavelength range between 280 and 320 nm (see Table 1.1). UV-B radiation, which has enough energy to damage the DNA molecule, is strongly absorbed by ozone. Radiation with wavelengths between 320 and 400 nm, referred to as UVA radiation, is relatively little affected by ozone. UV-A radiation can mitigate some of the damage inflicted by UV-B radiation (a phenomenon known as photo-repair), but it causes sunburn and is therefore believed to be a partial cause of skin cancer. In addition to the harmful effects on humans, too much UV radiation has deleterious effects on terrestrial animals and plants, as well as aquatic life forms.

In this book, we are mostly concerned with the flow of radiative energy through atmospheres and oceans. We will ignore polarization effects, which means that we disregard the Q, U, and V components of the Stokes vector, and consider only the first, radiance, component denoted by I. This approach is known as the scalar approximation, in contrast to the more accurate vector description. In general, this approximation is valid for longwave radiation where thermal emission and absorption dominate scattering processes. However, at short wavelengths where scattering is important, the radiation is generally partially polarized. For example, polarization is a basic part of a description of scattering of sunlight in a clear atmosphere or in pure water (so-called Rayleigh scattering). Generally, a coupling occurs between the various Stokes components, and an accurate description requires the full Stokes vector representation.

Previous analysis of polar mesospheric clouds (PMCs) observed by Solar Backscatter Ultraviolet (SBUV) instruments found that long-term variations in PMC brightness and occurrence frequency were anticorrelated with solar activity and that an increasing secular trend was present at most latitudes. In this paper, long-term PMC variations are presented in terms of ice water content (IWC), a physically based variable which is easier to interpret than previously reported UV albedo values. This model-based conversion from albedo to IWC removes most scattering angle effects. The derived long-term PMC variations in the SBUV data set are qualitatively the same using either an empirically derived adjustment for local time effects or no adjustment (i.e., assuming cancelation of interannual variations in tidally induced amplitude and/or phase). When we use stratospheric ozone variations as a proxy for mesospheric temperature changes, as suggested by recent model studies, we can explain more of the long-term IWC variability than if we use a linear trend. These results show that PMC ice water content in bright clouds increased rapidly from 1979 through the late 1990s and has been approximately constant from the late 1990s through 2013. The numerical value and sign of this trend during the last 15years depend on the choice of end points and latitude band. Simultaneously, the solar response of IWC observed by SBUV has weakened during the most recent cycle in the Northern Hemisphere, but increased in the Southern Hemisphere.

Polar Mesospheric Clouds (PMCs) are known to be influenced by changes in water vapor and temperature in the cold summertime mesopause. Solar variability of these constituents has been held responsible for 11-year and 27-day variability of PMC activity, although the detailed mechanisms are not yet understood. It is also known that the solar influence on PMC variability is a minor contributor to the overall day-to-day variability, which is dominated by effects of gravity waves, planetary waves, and interhemispheric coupling. To address this issue, we have analyzed 15 seasons of data taken from the Solar Occultation for Ice Experiment (SOFIE) on the Aeronomy of Ice in the Mesosphere (AIM) satellite. The SOFIE data contain precise measurements of water vapor, temperature and ice water content (among other quantities). These high-latitude measurements are made during the PMC season at the terminator, and therefore directly relate to the simultaneous measurements of mesospheric ice. Using a composite data set of Lyman-alpha irradiance, we correlated the time variation of the atmospheric variables with the 27-day variability of solar ultraviolet irradiance. We used a combination of time-lagged linear regression and Superposed Epoch Analysis to extract the solar contribution as sensitivity values (response/forcing) vs. height. We compare these results to previously published results, and show that the temperature sensitivity is somewhat higher, whereas the water sensitivity is nearly the same as published values. The time lags are shorter than that expected from direct solar heating and photodissociation, suggesting that the responses are due to 27-day variations of vertical winds. An analytic solution for temperature changes forced by solar irradiance variations suggests that if the response is due purely to Lyman-alpha heating and Newtonian cooling, the response should vary throughout the summertime season and depend primarily upon the height-dependent column density of molecular oxygen. (C) 2015 Elsevier Ltd. All rights reserved.

Nadir viewing observations of Polar Mesospheric Clouds (PMCs) from the Cloud Imaging and Particle Size (UPS) instrument on the Aeronomy of Ice in the Mesosphere (AIM) spacecraft are compared to Common Volume (CV), limb-viewing observations by the Solar Occultation For Ice Experiment (SOFIE) also on AIM. CIPS makes multiple observations of PMC-scattered UV sunlight from a given location at a variety of geometries and uses the variation of the radiance with scattering angle to determine a cloud albedo, particle size distribution, and Ice Water Content (IWC). SOFIE uses IR solar occultation in 16 channels (0.3-5 mu m) to obtain altitude profiles of ice properties including the particle size distribution and IWC in addition to temperature, water vapor abundance, and other environmental parameters. CIPS and SOFIE made CV observations from 2007 to 2009. In order to compare the CV observations from the two instruments, SOFIE observations are used to predict the mean PMC properties observed by CIPS. Initial agreement is poor with SOFIE predicting particle size distributions with systematically smaller mean radii and a factor of two more albedo and IWC than observed by CIPS. We show that significantly improved agreement is obtained if the PMC ice is assumed to contain 0.5% meteoric smoke by mass, in agreement with previous studies. We show that the comparison is further improved if an adjustment is made in the CIPS data processing regarding the removal of Rayleigh scattered sunlight below the clouds. This change has an effect on the CV PMC, but is negligible for most Of the observed clouds outside the CV. Finally, we examine the role of the assumed shape of the ice particle size distribution. Both experiments nominally assume the shape is Gaussian with a width parameter roughly half of the mean radius. We analyze modeled ice particle distributions and show that, for the column integrated ice distribution, Log-normal and Exponential distributions better represent the range of masses that contribute to the IWC. We further show that agreement between SOFIE and CIPS is further improved with the assumption of either Log-normal or Exponential ice particle size distributions. This improvement suggests that the range of mass bearing particle radii is larger, but not significantly shifted from what is obtained by assuming a Gaussian distribution. The assumption of an Exponential particle size distribution, as shown to be justifiable here, has the attractive benefits of being characterized with a single parameter, the mean radius, which greatly facilitates studies of the spatial and temporal variation of PMC particle size distributions as well as comparisons between observations and models. Overall, our results represent a validation of both the CIPS and SOFIE datasets. (C) 2015 Published by Elsevier Ltd.

This chapter contains sections titled: Introduction PMC Climatology from the SME and Nimbus Satellite Data Correlation With Solar Lyman Alpha Flux Theory of the Brightness Distribution of Polar Mesospheric Clouds Discussion and Conclusions

This paper describes an investigation using data from the Solar Backscatter Ultraviolet (SBUV) satellite instruments to explore and understand variations in the timing of the onset of Polar Mesospheric Cloud (PMC) seasons. Previous work has shown that for several recent southern hemisphere (SH) seasons, the PMC season onset was controlled by the timing of the shift from winter to summer zonal wind flow in the SH stratosphere. We extend the analysis of PMC season onset to 28 years of SBUV observations, including both hemispheres. A multiple linear regression analysis of SBUV data from 1984 to 2011 suggests that the SH PMC season onset is delayed by one day for every day that the zonal wind at 65°S and 50 hPa (∼20 km) remains in a winter‐like state. In addition, we find that the solar cycle plays a role: The SH season onset is delayed by about ten days at solar maximum compared to solar minimum. In the NH, the PMC season onset is delayed by ∼7 days at solar maximum compared to solar minimum; variations in the NH stratospheric wind, however, are not correlated with the NH onset date. On the other hand, inter‐hemispheric teleconnections are important in the NH; a one‐day shift in the NH season onset corresponds to a shift of ∼1.4 m/s in the SH stratospheric wind at 60.0°S and 20 hPa (∼26 km). Neither the NH nor the SH season onset date is correlated with the Quasi‐Biennial Oscillation, North Atlantic Oscillation, Arctic Oscillation, or El Niño Southern Oscillation.

The Ozone Monitoring Instrument (OMI) on the Aura satellite obtains unique measurements for polar mesospheric cloud (PMC) analysis. Its wide cross-track viewing swath and high along-track spatial resolution makes it possible to directly evaluate PMC occurrence frequency and brightness variations between 65° and 85° latitude as a function of local time over a 12–14h continuous period. OMI PMC local time variations are closely coupled to concurrent variations in measurement scattering angle, so that ice phase function effects must be considered when interpreting the observations. Two different phase functions corresponding to bright and faint clouds are examined in this analysis. OMI observations show maximum frequency and albedo values at 8–10h local time in the Northern Hemisphere, with decreasing amplitude at higher latitudes. Southern Hemisphere values reach a minimum at 18–20h LT. Larger variations are seen in Northern Hemisphere data. No statistically significant longitudinal dependence was seen.