Amal Chandran

ABSTRACT The Cloud Imaging and Particle Size (CIPS) experiment is one of the three instruments on board the Aeronomy of Ice in the Mesosphere (AIM) spacecraft that was launched into sun-synchronous orbit on April 25, 2007. CIPS is a 4 camera wide-field (120° x 80°) imager designed to measure PMC morphology and particle properties and has a spatial resolution of 1 x 2 km in the nadir. One of the objectives of AIM is to investigate gravity wave effects on PMC formation and evolution. In this work we present an analysis of gravity waves observed in PMC's near 80 - 85 km altitude in both Northern and Southern hemisphere summers of 2007 - 2008 season. We present maps of polar gravity wave activity in both hemispheres. The observed gravity waves will be analyzed for hemispherical similarities or differences. The gravity waves detected shall be analyzed for any variations in wave scales which show a seasonal or latitudinal dependence.

ABSTRACT The Cloud Imaging and Particle Size (CIPS) experiment is one of three instruments on board the Aeronomy of Ice in the Mesosphere (AIM) spacecraft that was launched into a 600 km sun-synchronous orbit on April 25, 2007. CIPS images have shown clear and distinct wave patterns and structure in Polar Mesospheric Clouds (PMCs), around the summertime mesopause region, which are qualitatively similar to ground based photographs of Noctilucent Clouds (NLCs). These structures, observed in PMCs, are interpreted as manifestations of upward propagating gravity waves. One of the objectives of the AIM mission is to investigate gravity wave effects on PMC formation and evolution. In this presentation we provide new results pertaining to the longitudinal variability of observed PMC wave structures from CIPS. The horizontal scales and maps of the observed PMC structures during the northern and southern hemisphere 2007 and 2008 cloud seasons are presented. By comparing the longitudinal variability of the normalized wave occurrence frequency with the CIPS observed PMC occurrence frequency and albedo we can infer new details about the effect of gravity waves on PMCs. The spatial variability of the observed longitudinal structures and correlation with topography are also presented.

We present preliminary results from a two dimensional version of the Community Aerosol and Radiation Model for Atmospheres (CARMA 2D) model of the effects of atmospheric gravity waves (AGW) on the brightness and existence of Polar Mesospheric Clouds (PMC). The model shows differences in the ice particle size and brightness of PMCs that depend on the spatial scale and period

Ground-based lidars have been used as a powerful tool to observe mesospheric clouds in both hemispheres covering the pole-to-pole regions. Rayleigh lidars have made significant contribu-tions to the study of gravity waves in stratosphere and mesosphere. In spite of the 40-50 km separation in altitude, Gerrard et al. [1998] found a negative correlation between the strato-spheric gravity waves at 30-45

ABSTRACT Noctilucent clouds (NLC), also calles polar mesospheric clouds (PMC), are the visible manifes-tation of ice particles in the polar summer mesopause region. Gravity waves are a key dynamical feature of the mesopause region and and can be observed when modulating noctilucent clouds. Cloud parameters like brightness or altitude of the layer show variabilities at different time scales, ranging from minutes to decades, and include tidal and solar cycle variations. Since 1997 NLC have been observed regularly by the ALOMAR Rayleigh/Mie/Raman (RMR) lidar in Northern Norway at 69N, 16E. The total of 4105 measurement hours are more or less evenly distributed over the 13 years in season and local time, NLC were detected during 1735 hours of these observations. Due to the unique instrumental setup consisting of two independently tiltable systems, the lidar can perform observations of NLC at two locations in the layer, saptially separated by up to 100 km. While the lidar can observe the cloud evolution at these two locations, the precise horizontal structure of the clouds cannot be defiend by the LIDAR alone. However, PMC are observed with the CIPS instrument onboard the AIM satellite with an unprecedented horizontal resolution of about 5 km. In addition to the instrument's high spatial resolution, the large field of view provides an excellent opportunity for coincident observations with the lidar. The combined data from the two instruments allows a unique study of the temporal and horizontal structure of the clouds. We will report initial results from the abalysis of coincident CIPS and LIDAR data for the years 2007 to 2009.

ABSTRACT Multiple stratospheric sudden warming (SSW) events have been spontaneously generated in simulations of the period between 1953-2006 by the Whole Atmosphere Community Climate Model (WACCM). These SSWs include extreme events where the polar vortex breaks down throughout the stratosphere and an elevated stratopause reforms at a high altitude. Several such events have recently been documented in the Arctic winter. While the SSW is triggered by breaking planetary waves, the role of gravity waves in the formation of the elevated stratopause, reformation of the polar vortex, and coupling between the stratosphere, mesosphere, and lower thermosphere remains a topic of current research. In this study we analyze the general circulation and dynamics of the mesosphere during both winters with extreme warming events and those with minor warming events. The dynamics of the free-running WACCM simulations are compared with WACCM simulations for the period between January 2004 to December 2007 that are forced up to 40 km with assimilated data from the Goddard Earth Observing system Model version 5 (GEOS-5). We quantify the longitudinal variations in the meridional and zonal circulation and wave-forcing of the model simulations and assess the relative contributions of planetary and gravity waves to the circulation during these events. We also determine the frequency of occurrence of SSW events and elevated stratopause events over the 53 winters in the free running version of WACCM and assess the inter-annual variability in the polar circulation.

ABSTRACT Stratospheric sudden warmings (SSW) are a dynamical phenomenon that occurs in the wintertime middle atmosphere. SSW events occur much more frequently in the northern hemisphere (NH) compared to the southern hemisphere (SH). In multiple simulations of the period 1953-2006 in the Whole Atmosphere Community Climate Model (WACCM), SSW events are generated spontaneously in both the Arctic as well as Antarctica. While multiple SSW events in the Arctic have been studied in detail from both observations and models, SSW events reported from Antarctica have been confined to observations of a major SSW event in 2002 and a minor SSW event in 2010. In this study we present a detailed analysis of multiple WACCM generated SSW events in the Antarctic and compare the response of the stratosphere and MLT region during the SSW events to responses in the Arctic. We also present comparisons in the planetary wave activity in the NH and SH, which constitute the triggering mechanism for the SSW events as well as the gravity wave forcing during these events. We find that almost all SSW events in Antarctica are minor SSW and are almost always late winter events occurring in late September, similar to the 2002 SSW event. We also present detailed analysis of a mid-winter SH SSW, which is an extremely rare event. The planetary wave activity triggering the SSW in the SH in WACCM appears to be wave 2, while in the NH it is predominantly wave 1. The occurrence frequency of all (minor plus major) SSW in the SH is ~ 0.18/year compared to ~ 0.94/year in the NH.

ABSTRACT Noctilucent clouds (NLC) are the visible manifestation of ice particles in the polar summer mesopause region. These clouds are often modulated by gravity waves on scales of seconds and a few 100 m. Since 1997 NLC have been observed regularly by the ALOMAR Rayleigh/Mie/Raman (RMR) lidar in Northern Norway at 69N, 16E. Only recently the lidar was upgraded to allow higher temporal resolution. Now the modulation of the NLC layer can be observed with sub-second time resolution even during daytime. The lidar also uses a molecular absorption spectrometer to calculate Doppler winds in the strato- and mesosphere. In combination with simultaneous temperature and aerosol measurements the propagation of gravity waves can be investigated. We present high resolution lidar observations of waves in NLC. We observe that the spectrum of fluctuations follows those of saturated gravity waves down to the signal to noise limit of about 10 seconds. Using the capability of the lidar to perform observations at two different locations in the NLC layer we compare those to satellite observations by the cloud imaging and particle size (CIPS) instrument with a horizontal resolution of about 5 km. We observe that the horizontal and temporal structure agrees well only when taking coincident (<10min) and common volume (<10 km) observations. We present initial results on the propagation of waves in temperature and wind throughout the middle atmosphere.

ABSTRACT The Aeronomy of Ice in the Mesosphere (AIM) satellite was designed specifically to investigate the nature and evolution of Polar Mesospheric Clouds (PMCs) which form near the high-latitude summer mesopause region. Of key importance is the investigation of the role of atmospheric dynamics on PMC formation and variability. In particular, gravity waves are known to strongly influence the dynamics of the upper atmospheric environment in which the PMCs nucleate and grow, but measurements of their characteristics in the summer polar mesosphere are few. The Cloud Imaging and Particle Size experiment (CIPS) on AIM is a four camera, wide-field (120° x 80°) UV imager capable of imaging PMC morphology and measuring gravity waves in exceptional detail, and over a broad range of scale sizes. Seven seasons of PMCs have now been imaged by CIPS since AIM was launched (April, 2007) providing a rich data base for investigating the characteristics and impact of gravity waves on the PMC morphology with high spatial resolution (5km). In this talk, we will compare recent gravity wave results using CIPS PMC data over the northern and southern hemispheric polar regions.

The Cloud Imaging and Particle Size (CIPS) Experiment on the Aeronomy of Ice in the Mesosphere Mission (AIM) has the ability to image Polar Mesospheric Clouds (PMC) with approximately 2 km resolution. In addition, the CIPS has a large field of view that allows the same region of space (at high latitude) to be viewed on several successive orbits with

... Diego Janches,1 Craig J. Heinselman,2 Jorge L. Chau,3 Amal Chandran,4 and Ronald Woodman3 ... order of magnitude, from $7 to 250 tons of material a day over the whole planet [Hughes, 1978; Wasson and Kyte, 1987; Love and Brownlee, 1993; Taylor, 1995; Mathews et ...

ABSTRACT In this paper we report winds and temperature in the mesopause region (80-102 km) over full diurnal cycles during the 2009 major Sudden Stratospheric Warming (SSW) at Fort Collins (41°N, 105°W). The measurements were made with the Colorado State University (CSU) sodium Doppler wind-temperature lidar. We deduce the diurnal mean wind and temperature profiles by removing the tidal components from the 24-h continuous observations and present their anomalous behaviors in connection with this event. These mean wind and temperature measurements reveal significant anomalies in the mesopause region: the mean temperature at 80 km was approximately 30 K lower than the climatological mean; the mean zonal wind ranged between ˜ -10 to 0 m/s from 80 to 97 km and then turned eastward in lower thermosphere in a reversal of the climatological mean wind profile. We further use observations from the TIMED/SABER satellite observations and simulations from the WACCM model to investigate the global structure of this dynamical anomaly at Fort Collins. The satellite observations and model reveal that the anomaly is part of a disturbance that extended from the polar region to Fort Collins. These simultaneous wind- and temperature-lidar observations document the direct impact of a major SSW on the dynamic and thermal circulation of the midlatitude mesopause region.

A synchronized observation of a noctilucent cloud (NLC) using an airborne camera and a polar mesospheric cloud (PMC) using spaceborne cameras was obtained on 6 July 2009. Two Canon EOS-30D cameras were integrated to a Mooney M20K research aircraft and flown to a location of 58.32°N, 112.30OW in Northern Alberta, Canada to coordinate with the overpass of the Aeronomy of

Mid-latitude mesospheric clouds (MCs) are a rare phenomenon and their existence is not well understood, as the mesosphere at these latitudes is, in general, too warm for clouds to form. During the 2009 northern hemisphere summer season an unusually high number of these clouds were reported over both central and southern Europe, and the western contiguous United States. In this

Simultaneous and common volume observations of Noctilucent Clouds (NLC) and Polar Mesospheric Clouds (PMC) have been performed above the ALOMAR research station in Northern Norway (69° N, 16° E) from ground and space, respectively. A detailed case ...