Hemisphere Summer Research Articles

General circulation modeling of the Martian upper atmosphere during global dust storms

Simulations with a general circulation model (GCM) have been performed to study the Martian upper atmosphere during two major dust storms. The GCM extending from the surface to about 160 km included a spectral parameterization of subgrid‐scale gravity waves suitable for planetary thermospheres, and prescribed four‐dimensional dust distributions corresponding to storm events near the equinox and solstice (Martian years 25 and 28, respectively). The results show that the wind and temperature fields in the upper atmosphere above ∼100 km respond to such storms as intensively as in the lower atmosphere. During the equinoctial storm, the temperature above the mesopause dropped by up to 30 K everywhere except in the Northern Hemisphere high latitudes, where it rose by up to 15 K. At the solstitial storm, the temperature above the mesopause decreased by up to 40 K in the winter hemisphere, by 15 K in the summer hemisphere, and increased by 30–40 K in tropics and in the summer hemisphere above 130 km. Prograde and retrograde zonal wind jets intensified throughout the atmosphere at all heights and during both dust scenarios. These changes are the result of the altered meridional overturning circulation induced by resolved and unresolved waves. Atmospheric density during dust storms enhanced in average by a factor of 2 to 3 in the mesosphere and lower thermosphere, which agrees well with observations.

General circulation modeling of the Martian upper atmosphere during global dust storms

[1] Simulations with a general circulation model (GCM) have been performed to study the Martian upper atmosphere during two major dust storms. The GCM extending from the surface to about 160 km included a spectral parameterization of subgrid-scale gravity waves suitable for planetary thermospheres, and prescribed four-dimensional dust distributions corresponding to storm events near the equinox and solstice (Martian years 25 and 28, respectively). The results show that the wind and temperature fields in the upper atmosphere above ∼100 km respond to such storms as intensively as in the lower atmosphere. During the equinoctial storm, the temperature above the mesopause dropped by up to 30 K everywhere except in the Northern Hemisphere high latitudes, where it rose by up to 15 K. At the solstitial storm, the temperature above the mesopause decreased by up to 40 K in the winter hemisphere, by 15 K in the summer hemisphere, and increased by 30–40 K in tropics and in the summer hemisphere above 130 km. Prograde and retrograde zonal wind jets intensified throughout the atmosphere at all heights and during both dust scenarios. These changes are the result of the altered meridional overturning circulation induced by resolved and unresolved waves. Atmospheric density during dust storms enhanced in average by a factor of 2 to 3 in the mesosphere and lower thermosphere, which agrees well with observations.

The magnitude and inter-hemispheric asymmetry of equatorial ionization anomaly-based on CHAMP and GRACE observations

Based on nearly nine years (2001–2009) of observations from CHAMP and GRACE, a comprehensive study has been made on the morphology of the equatorial ionization anomaly (EIA), focusing on the EIA's magnitude, inter-hemispheric asymmetry by resolving their seasonal and local time variations at different altitudes and solar activity levels. The electron density and the magnetic latitudes of the EIA crests both peak around 1400 LT while the crest-to-trough ratio (CTR) of the EIA reaches its highest value post-sunset around 2000 LT, with a value almost twice the daytime level. The magnetic latitude of the EIA at CHAMP altitude (~400km) can reach 13° around December solstice during both high and low solar activity years, while at GRACE altitude (~480km) the crests are observed much closer to the dip equator during low solar activity years. During high solar activity years the averaged apex height of the EIA crests can reach 800km. During solstice seasons a clear inter-hemispheric asymmetry of the EIA can be seen. At CHAMP altitude the electron density of the EIA crest is stronger in the winter hemisphere during morning to noontime hours. It reverses after the noontime and the transition time appears around 1400 LT and 1200 LT for high and low solar activity years, respectively. At higher altitude (GRACE), the electron density of the EIA crest is always stronger in the summer hemisphere over the whole daytime. Simulation results from the SAMI2 model also show the differences in EIA inter-hemisphere asymmetry at the two altitudes.

Dominant modes of geopotential height in the northern hemisphere in summer on interdecadal timescales

Empirical orthogonal function (EOF) analysis is performed on the field of the northern hemisphere geopotential height at 200-hPa using a 54-year (1958–2011) record of summer data on an interdecadal time scale. The first dominant mode, which shows smooth semi-hemispheric variation with maximum action centers in the western hemisphere in the mid-latitudes over the eastern Pacific, North America, and the North Atlantic, is related to global warming. The second mode, which has a pronounced tropical-extratropical alternating pattern with active centers located over the eastern hemisphere from Western Europe across East Asia to the western Pacific, has a close relationship with the Arctic Oscillation. Further analysis results indicate that the two dominant modes show good correlation with the Arctic sea ice concentration (SIC), with correlation coefficients between these two modes and the first two EOF modes of the Arctic SIC reaching 0.88 and 0.86, respectively.

Hemisphere-coupled modeling of nighttime medium-scale traveling ionospheric disturbances

Nighttime medium-scale traveling ionospheric disturbances (MSTIDs), which have tilted frontal structures in the midlatitude ionosphere, are investigated by the midlatitude ionosphere electrodynamics coupling (MIECO) model in this study. It has been proposed that the electrodynamic coupling between the E and F regions plays an important role in generating MSTIDs within a few hours. An intriguing aspect of MSTIDs is that they were simultaneously observed at magnetic conjugate locations in the Northern and Southern Hemispheres. In order to study the hemisphere-coupled electrodynamics, the MIECO model has been upgraded to consist of two simulation domains for both hemispheres in which the electrostatic potential is solved by considering electrodynamics in both hemispheres. The simultaneous occurrence of MSTIDs at the magnetic conjugate stations has clearly been reproduced when the F-region neutral wind satisfies the unstable condition in both hemispheres and a sporadic-E layer is given only at the Northern (summer) Hemisphere. Even if the unstable condition is satisfied in the summer hemisphere, an unfavorable F-region neutral wind in the winter hemisphere largely suppresses the growth of MSTIDs in both hemispheres.

A Global View on the Swell and Wind Sea Climate by the Jason-1 Mission: A Revisit

Abstract In this study, a global climatology of swells and wind seas was investigated using near-10-yr collocated wind speed and significant wave height (SWH) measurements from the basic Geophysical Data Record (GDR) of the Jason-1 mission. A statistical method to estimate the wind sea and swell SWHs, respectively, on the basis of wave energy and wind sea/swell probability was proposed. The global distributions of swell/wind sea probability displayed the swell's dominance in the World Ocean. Their seasonal variation showed not only the regions called “swell pools” with high swell probability throughout the year at low latitudes, which have been found in previous studies, but also the regions with high swell probability only in hemispheric summer, termed “seasonal swell pools,” located at the midlatitudes of open oceans. The seasonal geographical patterns of the swell SWH were similar to those of the SWH due to the swell's dominance, and the patterns of the wind SWH were similar to those of the wind speed because of their well-coupled nature. The results could be used as a reference for related applications such as ocean engineering, seafaring, validation of wave models, and studies on climate change.

Prediction of global patterns of dominant quasi-biweekly oscillation by the NCEP Climate Forecast System version 2

Daily output from the hindcasts by the National Centers for Environmental Prediction (NCEP) Climate Forecast System version 2 (CFSv2) is analyzed to understand the skill of forecasting atmospheric variability on quasi-biweekly (QBW) time scale. Eight dominant quasi-biweekly oscillation (QBWO) modes identified by the extended empirical orthogonal function analysis are focused. In the CFSv2, QBW variability exhibits a significant weakening tendency with lead time for all seasons. For most QBWO modes, the variance drops to only 50 % of the initial value at lead time of 11–15 days. QBW variability has better prediction skill in the winter hemisphere than in the summer hemisphere. Skillful forecast can reach about 10–15 days for most modes but those in the winter hemisphere have better forecast skills. Among the eight QBWO modes, the North Pacific mode and the South Pacific (SP) mode have the highest forecast skills while the Asia–Pacific mode and the Central American mode have the lowest skills. For the Asia–Pacific and Central American modes, the forecasted QBWO phase shows an obvious eastward shift with increase in lead time compared to observations, indicating a smaller propagating speed. However, the predicted feature for the SP mode is more realistic. Air–sea coupling on the QBW time scale is perhaps responsible for the different prediction skills for different QBWO modes. In addition, most QBWO modes have better forecasting skills in El Nino years than in La Nina years. Different dynamical mechanisms for various QBWO modes may be partially responsible for the differences in prediction skill among different QBWO modes.

Investigation of the interhemispheric asymmetry in reverse convection near solstice during northward interplanetary magnetic field conditions using MHD simulations

AbstractThe reverse convection potential under northward interplanetary magnetic field (IMF) is significantly larger in the summer ionosphere than in the winter. In this study, we use the Coupled Magnetosphere‐Ionosphere‐Thermosphere model to simulate a Northern Hemisphere winter event where observations have shown asymmetry in both the reverse convection strength between hemispheres and the magnetic field topology associated with the ionospheric reverse convection cells. We show that a topological asymmetry, in which reconnection between the geomagnetic field and the IMF occurs in the summer hemisphere, first drives the interhemispheric asymmetry in reverse convection strength rather than an interhemispheric asymmetry in ionospheric conductivity. We find a large amount of overdraped open magnetic flux connected to the summer hemisphere that results from this reconnection bypasses the winter hemisphere x line and reconnects with the IMF again in the summer hemisphere lobe. This leads to a large amount of circulating lobe flux in the summer hemisphere and stagnant lobe flux in the winter hemisphere, while maintaining a divergence‐free field, as well as the weaker reverse convection potential in the winter hemisphere ionosphere.

Retrieval of polar mesospheric cloud properties from CIPS: Algorithm description, error analysis and cloud detection sensitivity

The Cloud Imaging and Particle Size (CIPS) instrument has been in operation on the NASA Aeronomy of Ice in the Mesosphere (AIM) satellite since May 2007. CIPS is a multi-camera UV imager that makes unprecedented hemispheric-scale measurements of polar mesospheric clouds (PMC). The primary CIPS data products are cloud frequency, albedo, mean particle radius, ice water content and vertical column particle density. These quantities are retrieved at 25km2 resolution at latitudes between ~55° and 84° over a range of local times in the summer hemisphere. CIPS has obtained data for six Northern Hemisphere and five Southern Hemisphere PMC seasons to date and is still in operation and performing flawlessly. The CIPS data are made available to the scientific community in a variety of formats and spatial and temporal resolution, including full-resolution single-orbit level 2 data files and images, daily (hemispheric) albedo maps and images, and full-season latitude-binned summary files. In this paper we describe the CIPS measurement strategy and sampling characteristics, calibration and the Version 4.20 processing algorithms and retrievals. We also provide a quantitative evaluation of the CIPS cloud detection sensitivity and estimated random and systematic errors of the V4.20 cloud data products.

The effect of ocean mixed layer depth on climate in slab ocean aquaplanet experiments

The effect of ocean mixed layer depth on climate is explored in a suite of slab ocean aquaplanet simulations with different mixed layer depths ranging from a globally uniform value of 50–2.4 m. In addition to the expected increase in the amplitude of the seasonal cycle in temperature with decreasing ocean mixed layer depth, the simulated climates differ in several less intuitive ways including fundamental changes in the annual mean climate. The phase of seasonal cycle in temperature differs non-monotonically with increasing ocean mixed layer depth, reaching a maximum in the 12 m slab depth simulation. This result is a consequence of the change in the source of the seasonal heating of the atmosphere across the suite of simulations. In the shallow ocean runs, the seasonal heating of the atmosphere is dominated by the surface energy fluxes whereas the seasonal heating is dominated by direct shortwave absorption within the atmospheric column in the deep ocean runs. The surface fluxes are increasingly lagged with respect to the insolation as the ocean deepens which accounts for the increase in phase lag from the shallow to mid-depth runs. The direct shortwave absorption is in phase with insolation, and thus the total heating comes back in phase with the insolation as the ocean deepens more and the direct shortwave absorption dominates the seasonal heating of the atmosphere. The intertropical convergence zone follows the seasonally varying insolation and maximum sea surface temperatures into the summer hemisphere in the shallow ocean runs whereas it stays fairly close to the equator in the deep ocean runs. As a consequence, the tropical precipitation and region of high planetary albedo is spread more broadly across the low latitudes in the shallow runs, resulting in an apparent expansion of the tropics relative to the deep ocean runs. As a result, the global and annual mean planetary albedo is substantially (20 %) higher in the shallow ocean simulations which results in a colder (7C) global and annual mean surface temperature. The increased tropical planetary albedo in the shallow ocean simulations also results in a decreased equator-to-pole gradient in absorbed shortwave radiation and drives a severely reduced (≈50 %) meridional energy transport relative to the deep ocean runs. As a result, the atmospheric eddies are weakened and shifted poleward (away from the high albedo tropics) and the eddy driven jet is also reduced and shifted poleward by 15° relative to the deep ocean run.

Contributions of Individual Atmospheric Diabatic Heating Processes to the Generation of Available Potential Energy

Abstract The generation of zonal and eddy available potential energy (Gz and Ge) as formulated by Lorenz are computed on a global-, daily-, and synoptic-scale basis to consider the contribution of each diabatic heating component separately and in combination. Using global, mostly satellite-derived datasets for the diabatic heating components and the temperature enables us to obtain Gz and, especially, Ge from observations for the first time and at higher temporal and spatial resolution than previously possible. The role of clouds in maintaining G is investigated. The global annual mean Gz is 1.52 W m−2. Values reach a minimum of 0.63 W m−2 in the Northern Hemisphere during spring and a maximum of 2.27 W m−2 in the Southern Hemisphere during winter. The largest contributors to Gz are latent heating in the tropical upper troposphere, associated with the intertropical convergence zone in the summer hemisphere and surface sensible heat fluxes in the winter pole. Diabatic cooling by radiative fluxes (mostly longwave) generally destroys Gz. The value of Ge is negative and is about an order of magnitude smaller than Gz, with a global annual mean of −0.29 W m−2. However, the small value of Ge results from the cancellation of the contributions from the individual diabatic heating terms, which are actually roughly similar in magnitude to their Gz contributions. The results presented herein suggest that the large-scale dynamics of the atmosphere organize the spatial and temporal distribution of clouds and precipitation in such a way as to increase the energy available to drive the circulation, a kind of positive feedback.

An investigation of the formation patterns of the ionospheric F3 layer in low and equatorial latitudes

Ionogram traces with the F3 layer in different latitude do not always seem similar. In our work, we tend to describe morphological features of traces with the F3 layer in magnetic low-latitude region and near magnetic equator through the quantitative investigation of the diurnal variation and latitude dependence of two morphologically characteristic parameters – the foF2-to-foF3 ratio and the difference between h′F3 and h′F2 – in geomagnetically quiet period. The distribution of two formation patterns (pattern A and pattern B are defined with increasing F3 peak density and with nearly constant or decreasing F3 peak density respectively as the peak moving upward around the onset of the F3 layer’s occurrence) of the F3 layer is also investigated based on statistics of formation patterns of the F3 layer in Sanya and Kwajalein in 2011. The ideal equinoctial distribution (without the summer-to-winter neutral wind) of those patterns is symmetrical about magnetic equator with pattern A in magnetic low-latitude region and pattern B near magnetic equator. When taking the summer-to-winter neutral wind which resists (enhances) the plasma diffusion to higher latitude in the windward (leeward) into consideration in a solstice, pattern A could be observed near magnetic equator in summer hemisphere and pattern B in magnetic low-latitude region in winter hemisphere compared with the ideal distribution in the equinox.

The Hadley Circulation in Reanalyses: Climatology, Variability, and Change

Abstract Analysis of the annual cycle of intensity, extent, and width of the Hadley circulation across a 31-yr period (1979–2009) from all existent reanalyses reveals a good agreement among the datasets. All datasets show that intensity is at a maximum in the winter hemisphere and at a minimum in the summer hemisphere. Maximum and minimum values of meridional extent are reached in the respective autumn and spring hemispheres. While considering the horizontal momentum balance, where a weakening of the Hadley cell (HC) is expected in association with a widening, it is shown here that there is no direct relationship between intensity and extent on a monthly time scale. All reanalyses show an expansion in both hemispheres, most pronounced and statistically significant during summer and autumn at an average rate of expansion of 0.55° decade−1 in each hemisphere. In contrast, intensity trends are inconsistent among the datasets, although there is a tendency toward intensification, particularly in winter and spring. Correlations between the HC and tropical and extratropical large-scale modes of variability suggest interactions where the extent of the HC is influenced by El Niño–Southern Oscillation (ENSO) and the annular modes. The cells tend to shrink (expand) during the warm (cold) phase of ENSO and during the low (high) phase of the annular modes. Intensity appears to be influenced only by ENSO and only during spring for the southern cell and during winter for the northern cell.

Role of gravity waves in the forcing of quasi two‐day waves in the mesosphere: An observational study

AbstractAmplitudes of quasi two‐day waves (QTDWs) are derived from temperature observations of the High Resolution Dynamics Limb Sounder and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite instruments. In particular, a global climatology of QTDW amplitudes is derived from 10 years of SABER data, covering the mesosphere and lower thermosphere. This climatology is compared with geostrophic winds and climatologies of gravity wave (GW) momentum flux and GW drag absolute values derived from the same data set. We find that QTDWs are forced shortly after the maximum of the mesospheric summertime zonal wind jet in regions of jet instability where the meridional gradient of quasi‐geostrophic zonal mean potential vorticity is strongly negative. The jet instability regions are closely linked to enhanced GW drag that likely seeds those instabilities by decelerating the jet and causing the jet curvature responsible for the negative potential vorticity gradient. The vertical phase structure and the Eliassen‐Palm flux of the QTDWs are derived from SABER data and investigated. It is shown that QTDWs propagate upward starting from the jet instability regions. They exert eastward drag in the jet core, and strong westward drag at higher altitudes. Strikingly, the QTDWs are forced in regions where the global distribution of GWs exhibits a characteristic longitudinal structure caused by the GW source patterns in the summer hemisphere. This longitudinal structure might play an important role in the forcing of QTDWs; however, no clear link has been found to the observed QTDW zonal wavenumbers.

History, distribution, and seasonal abundance of the Least Tern Sternula antillarum (Aves: Charadriiformes: Sternidae) in Brazil

We review existing data on the distribution of the Least Tern, Sternula antillarum along the Brazilian coast, based on the literature and museum specimens, and present results of a year-long study (October 2008 to September 2009) on the seasonal abundance of this species on a large tidal flat area, Cajuais Bank, in the State of Ceara, north-eastern Brazil. We evaluate whether the observed variation in the abundance of terns is due to the occurrence of an undocumented breeding colony, or alternatively, whether it results from an influx of migrants from the Northern Hemisphere. The recovery of historical data revealed that all literature references on the distribution of birds in the Americas, published up to the late 1990s include Brazil in the non-breeding range of the Least Tern. This inclusion is based on a few, old (late 19th and early 20th centuries) museum specimens, all of which have been collected on the northern and north-eastern coasts of this country'. From the late 1980s, birds continued to be occasionally recorded along the coastline, running from the State of Amapa (01°N) up to the State of Bahia (10°S), with records of single individuals in south-eastern and southern Brazil. An alleged record from Rocas Atoll, 260 km off the Brazilian mainland, might tentatively refer to the Old World Little Tern S. albifrons. At Cajuais Bank, Least Terns occurred from October 2008 to April 2009, and in September 2009. The highest numbers (> 800 individuals) were recorded in January-February (Southern Hemisphere's summer). The species was observed in rather small numbers (< 30) in March-April (early-mid Southern Hemisphere fall) and in September (early Southern Hemisphere spring), being absent from the area in May-August (Southern Hemisphere's fall and winter). In October-December 2008 (Southern Hemisphere's spring), and September 2009 (early Southern Hemisphere's summer), no birds were in breeding plumage. In January, about 32% of the birds were in breeding plumage, while from February-April (Southern Hemisphere's summer to mid fall) all were in breeding plumage. This pattern is consistent with what would be expected for migratory birds. The Cajuais Bank itself (and adjacent beaches and inland environments) holds the largest numbers of Least Terns recorded in Brazil, thus being one of the most significant sites along the migratory route of the species.

Operational assimilation of ozone‐sensitive infrared radiances at ECMWF

AbstractECMWF has been assimilating ozone‐sensitive infrared (IR/O3) radiances from AIRS, IASI, and HIRS in its operational system since November 2011. We present a detailed assessment of the value of assimilating these observations, as well as the steps that have been taken to successfully merge the infrared information with that provided by ozone products retrieved from UV sensors. In general, the assimilation of the IR/O3 radiances improves the agreement between the ozone analyses and independent ozone data from MLS and sondes, especially in the UTLS and at high latitudes in the Southern Hemisphere winter. However, blending the information provided by the IR/O3 radiances with that provided by UV instruments can lead in certain circumstances to a degradation of the ozone analyses in the region of the ozone maximum, particularly at midlatitudes in the summer hemisphere. It is shown that this problem can be alleviated by providing the assimilation system with height‐resolved ozone information. The assessment of one‐year long assimilation experiments has shown some additional problems in the ozone analyses related to a slow drift of adaptive observation bias correction over time. Previously, just two uncorrected infrared channels (one from AIRS and one from IASI) were used to stabilise (anchor) the bias correction of all other ozone observations against the influence of model systematic error. However, it has been found that their influence (limited primarily to the UTLS) was not sufficient to constrain the ozone assimilation system as a whole (i.e. the total column) over longer time‐scales of several months to a year. This issue has been addressed by using additional anchoring observations to constrain the time evolution of the bias correction.

Modes of interannual variability of Southern Hemisphere atmospheric circulation in CMIP3 models: assessment and projections

An assessment is made of the modes of interannual variability in the seasonal mean summer and winter Southern Hemisphere 500 hPa geopotential height in the twentieth century in models from the Coupled Model Intercomparison Project phase 3 (CMIP3) dataset. The analysis is done for both the intraseasonal and slow components of the geopotential height. When the CMIP3 models are assessed against reanalysis data, the spatial structure and variance of the leading modes in the intraseasonal component are generally well reproduced. There are systematic differences between the models in their reproduction of the leading modes in the slow component. An overall score using the leading modes in the slow component allows a categorisation of CMIP3 model performance. Using an ensemble from four models that suitably reproduce the twentieth century modes, modes of variability in the slow-internal and slow-external components are estimated. The leading mode of the slow-external component is shown to be related to observed changes in greenhouse gas concentrations. In this ensemble, there is little change in the leading modes in the intraseasonal component in the twenty-first century. Larger changes in variance, and subtle changes in regional-scale structure, are found for the leading modes in the slow-internal component. These are related to changes in the slowly varying dynamics of the Southern Annular Mode and the El Nino-Southern Oscillation. By far the biggest change is in the leading mode of the slow-external component. The spatial structure becomes uniform in the twenty-first century, and the variance increases with increasing greenhouse gas concentrations.

The zonal propagating characteristics of low-frequency oscillation over the Eurasian mid-high latitude in boreal summer

Using 32-yr National Centers for Environment Prediction-National Center for Atmospheric Research (NCEP-NCAR) reanalysis data, we investigated zonal propagation and circulation characteristics of the low-frequency circulation for the prevailing period over Eurasian mid-high latitude in boreal summer (May-August) in terms of empirical orthogonal function (EOF), linear regression, and phase analysis and so on. We found that the dominant periods of the low-frequency circulation are 10–30 days and it clearly shows meridional (southward) and zonal (westward) propagation features at the middle troposphere (500 hPa). The average zonal speed of the 10–30 days low-frequency oscillation (LFO) is about 9–10 longitudes per day. Further analysis shows that the southernmost part of the polar vortex in the northern hemisphere exhibits westward clockwise rotation in the eastern hemisphere in boreal summer. Also, the southernmost tips of 5400 and 5500 gpm contours, which indicate the site of the major trough in the eastern hemisphere, obviously move westwards. The southernmost tip of 5500 gpm contour line propagates westwards at the speed of about 9–10 longitudes per day, which is consistent with the mean zonal speed of the westward propagation of the low-frequency circulation. Moreover, the 10–30-day LFO-related cold air also shows west propagation feature with respect to LFO phases. The westward propagation of the LFO is the low-frequency-scale embodiment of the clockwise rotation of polar vortex. The cold air activities closely related to polar vortex or to ridge-trough system activities is the essential circulation of 10–30 days LFO circulation over the Eurasian mid-high latitude in boreal summer.

Central Venous Catheter Insertion by Registered Professional Nurses in the United States: Scope of Practice, Education, Training, and Credentialing Considerations

The USU time-dependent ionospheric model (TDIM) simulated the northern (winter) and southern (summer) ionospheres as they responded to the changing solar wind and geomagnetic activity on 14 January 1988. This period began with moderately disturbed conditions, but as the IMF turned northward, the geomagnetic activity decreased. By 1400 UT, the IMF By component became strongly negative with Bz near zero; and eventually Bz turned southward. This began a period of intense activity as a magnetic storm developed. The magnetospheric electric field and auroral electron precipitation drivers for these simulations were obtained from the Naval Research Laboratories (NRL) Magnetohydrodynamic (MHD) magnetospheric simulation for this event.The F-region ionospheric simulations contrast the summer–winter hemispheres. Then, the difference in how the two hemispheres respond to the geomagnetic storm is related to the differences in magnetospheric energy deposition in the two hemispheres. This also emphasizes the role played by the E-region in the magnetosphere–ionosphere (M–I) coupling and subsequent lack of conjugacy in the two hemispheres. The F-region’s response to the changing geomagnetic conditions also demonstrates a striking lack of conjugacy. This manifests itself in a well-defined ionospheric morphology in the summer hemisphere and a highly irregular morphology in the winter hemisphere. These differences are found to be associated with the differences in the magnetospheric electric field input.

Climatology and first-order composition estimates of mesospheric clouds from Mars Climate Sounder limb spectra

Mesospheric clouds have been previously observed on Mars in a variety of datasets. However, because the clouds are optically thin and most missions have performed surface-focussed nadir sounding, geographic and seasonal coverage is sparse. We present new detections of mesospheric clouds using a limb spectra dataset with global coverage acquired by NASA’s Mars Climate Sounder (MCS) aboard Mars Reconnaissance Orbiter. Mesospheric aerosol layers, which can be CO2 ice, water ice or dust clouds, cause high radiances in limb spectra, either by thermal emission or scattering of sunlight. We employ an object recognition and classification algorithm to identify and map aerosol layers in limb spectra acquired between December 2006 and April 2011, covering more than two Mars years. We use data from MCS band A4, to show thermal signatures of day and nightside features, and A6, which is sensitive to short wave IR and visible daytime features only. This large dataset provides several thousand detections of mesospheric clouds, more than an order of magnitude more than in previous studies.Our results show that aerosol layers tend to occur in two distinct regimes. They form in equatorial regions (30°S–30°N) during the aphelion season/northern hemisphere summer (Ls<150°), which is in agreement with previous published observations of mesospheric clouds. During perihelion/dust storm season (Ls>150°) a greater number of features are observed and are distributed in two mid-latitude bands, with a southern hemisphere bias. We observe temporal and longitudinal clustering of cloud occurrence, which we suggest is consistent with a formation mechanism dictated by interaction of broad temperature regimes imposed by global circulation and the propagation to the mesosphere of small-scale dynamics such as gravity waves and thermal tides.Using calculated frost point temperatures and a parameterization based on synthetic spectra we find that aphelion clouds are present in generally cooler conditions and are spectrally more consistent with H2O or CO2 ice. A significant fraction has nearby temperature retrievals that are within a few degrees of the CO2 frost point, indicating a CO2 composition for those clouds. Perihelion season clouds are spectrally most similar to H2O ice and dust aerosols, consistent with temperature retrievals near to the clouds that are 30–80K above the CO2 frost point.