Northern Hemisphere Spring Research Articles

Global Precipitation for the Year 2023 and How It Relates to Longer Term Variations and Trends

Global Precipitation for the Year 2023 and How It Relates to Longer Term Variations and Trends

Seasonal variations of orographic clouds on Mars with MRO/MARCI observations and the Mars Planetary Climate Model

Although an appreciable amount of research has been conducted studying the Aphelion Cloud Belt (ACB) and Polar Hoods (PHs), much less attention has been given to orographic clouds on Mars. Orographic clouds (afternoon) are generally observed in northern Spring and Summer since they are associated with the significant Martian volcanoes. The water ice optical depths near 15h00 LTST (Local True Solar Times) provided by the Mars Color Imager (MARCI) of Mars Reconnaissance Orbiter (MRO) are used to investigate seasonal and spatial variations of orographic clouds in four volcanic regions: Alba Patera, Olympus Mons, Tharsis region and Elysium Mons. The seasonal variations of water ice clouds over volcanic areas need to be better understood. Thus, context will be provided using the meteorological fields from the Mars PCM (Mars Planetary Climate Model led by the Laboratoire de Météorologie Dynamique Paris, France). This study provides a general picture of how Martian afternoon water ice clouds correlate with Mars PCM’s meteorological variables: water ice column, atmospheric temperature, meteorological winds, and water vapor mixing ratio. Comparison between the model and the MARCI observations show that spatial and seasonal variations of atmospheric temperature, water vapor, and meteorological winds strongly control the water ice cloud distribution during northern hemispheric Spring and Summer.

Hydroclimate Variability in the Equatorial Western Indian Ocean for the Last 250,000 Years

AbstractIndian Ocean sea surface temperatures impact precipitation across the basin through coupled ocean‐atmosphere responses to changes in climate. To understand the hydroclimate response over the western Indian Ocean and equatorial east Africa to different forcing mechanisms, we present four new proxy reconstructions from core VM19‐193 (2.98°N, 51.47°E) that span the last 250 ky. Sub‐surface water temperatures (Sub‐T; TEX86) show strong precessional (23 ky) variability that is primarily influenced by maximum incoming solar radiation (insolation) during the Northern Hemisphere spring season, likely indicating that local insolation dominates the upper water column at this tropical location over time. Leaf waxes, on the other hand, reflect two different precipitation signals: δ13Cwax (in phase with boreal fall insolation) is likely reflecting vegetation changes in response to local rainfall over east Africa, whereas δDprecip (primarily driven by boreal summer insolation) represents changes in regional circulation associated with the summer monsoon. Glacial‐interglacial changes in ocean temperatures support glacial shelf exposure over the Maritime Continent in the eastern Indian Ocean and the subsequent weakening of the Indian Walker Circulation as a mechanism driving 100 ky climate variability across the tropical Indo‐Pacific. Additionally, the 100 ky spectral power in δDprecip supports a basin‐wide weakening of summer monsoon circulation in response to glacial climates. Overall, the proxy records from VM19‐193 indicate that both precession and glacial‐interglacial cycles exert control over hydroclimate at this tropical location.

Abstract 13270: Seasonal Variation in In-Hospital Outcomes of Takotsubo-Syndrome-Related Admissions: A National Inpatient Analysis, 2019

Background: Contemporary literature lacks data on the impact of climatic variations on the etiopathogenesis and outcomes of Takotsubo Syndrome (TTS)-related hospitalization in the U.S. Methods: Seasonal variation was identified based on meteorological classification of the northern hemisphere Spring, Summer, Fall and Winter using data from the National Inpatient Sample (2019) and odds of outcomes were assessed using multivariable regression models. Results: The TTS cohort (n=41830) in 2019 was mostly caucasian (80.6%), female (82.1%), and median age ≥65yrs (61.9%). Fall (25.9%) admissions were the highest, followed by summer (25%), spring (24.6%) and winter (24.5%). Despite a similar median length of stay (4-days; p<0.001), winter hospitalization expenditures (USD56763) were the highest and fall lowest (USD51649). Winter admissions had greater all-cause mortality (7.3%vs.6.7%) and dysrhythmias (29.8%vs.28.5%), including Atrial fibrillation (AF) (20.7%vs. 19.7%). Admissions in spring had a higher cardiac arrest (4.8%vs.4.1%) and Acute Venous Thromboembolism (VTE) (4.7%vs.3.5%) compared to overall TTS-related admissions. When adjusted for confounders, a higher risk of dysrhythmias was noted for [winter (OR:1.20; 95%CI:1.03-1.39), Spring (OR:1.15;95%CI:1.00-1.33) and Fall (OR:1.18;95%CI:1.03-1.36) vs. summer; p=0.063]. A higher risk was also noted for AF in winter (OR:1.22;95%CI:1.02-1.45), Spring (OR:1.20;95%CI:1.02-1.42) and Fall (OR:1.28;95%CI:1.08-1.51) when compared to summer; p=0.028]. Spring admissions had a greater risk of VTE than summer admissions [(OR:1.54;95%CI:1.09-2.16) vs. summer; p=0.067]. Other outcomes, such as all-cause mortality and cardiogenic shock, had an association after controlling for confounding variables. Conclusions: Compared to Summer, Winter hospitalizations increased the risk of dysrhythmia and AF, while Spring admissions revealed a higher risk of VTE.

Review article: Global monitoring of snow water equivalent using high-frequency radar remote sensing

Abstract. Seasonal snow cover is the largest single component of the cryosphere in areal extent, covering an average of 46 × 106 km2 of Earth's surface (31 % of the land area) each year, and is thus an important expression and driver of the Earth's climate. In recent years, Northern Hemisphere spring snow cover has been declining at about the same rate (∼ −13 % per decade) as Arctic summer sea ice. More than one-sixth of the world's population relies on seasonal snowpack and glaciers for a water supply that is likely to decrease this century. Snow is also a critical component of Earth's cold regions' ecosystems, in which wildlife, vegetation, and snow are strongly interconnected. Snow water equivalent (SWE) describes the quantity of water stored as snow on the land surface and is of fundamental importance to water, energy, and geochemical cycles. Quality global SWE estimates are lacking. Given the vast seasonal extent combined with the spatially variable nature of snow distribution at regional and local scales, surface observations are not able to provide sufficient SWE information. Satellite observations presently cannot provide SWE information at the spatial and temporal resolutions required to address science and high-socio-economic-value applications such as water resource management and streamflow forecasting. In this paper, we review the potential contribution of X- and Ku-band synthetic aperture radar (SAR) for global monitoring of SWE. SAR can image the surface during both day and night regardless of cloud cover, allowing high-frequency revisit at high spatial resolution as demonstrated by missions such as Sentinel-1. The physical basis for estimating SWE from X- and Ku-band radar measurements at local scales is volume scattering by millimeter-scale snow grains. Inference of global snow properties from SAR requires an interdisciplinary approach based on field observations of snow microstructure, physical snow modeling, electromagnetic theory, and retrieval strategies over a range of scales. New field measurement capabilities have enabled significant advances in understanding snow microstructure such as grain size, density, and layering. We describe radar interactions with snow-covered landscapes, the small but rapidly growing number of field datasets used to evaluate retrieval algorithms, the characterization of snowpack properties using radar measurements, and the refinement of retrieval algorithms via synergy with other microwave remote sensing approaches. This review serves to inform the broader snow research, monitoring, and application communities on progress made in recent decades and sets the stage for a new era in SWE remote sensing from SAR measurements.

Diverse variations in middle and high latitudes of the Northern Hemisphere spring phenology sensitivity to diurnal temperature during 1982–2015

AbstractRecent studies have revealed that the influence of diurnal temperature on spring phenology is asymmetric, and the faster night‐time warming in the Northern Hemisphere (NH) has a complex impact on spring phenology. Our understanding from the sensitivity of the start of the growing season (SOS) to daytime (ST_daytime) and night‐time temperatures (ST_night‐time) has urgently needs to be improved. In this study, the SOS sensitivity to diurnal temperature in the middle and high latitudes of the NH (>30°N) from 1982 to 2015 is estimated. The results indicate that although SOS showed stronger sensitivity to daytime than night‐time temperature in most parts of the study areas, the influence of daytime temperature on SOS is decreasing, while the influence of night‐time temperature on SOS is increasing. The variations in ST_daytime and ST_night‐time along the latitude gradient were significantly correlated with the warming rate of the preseason diurnal temperature (p < .01). The SOS between 40°N and 70°N was more sensitive to daytime temperature, while ST_night‐time was higher than ST_daytime at other latitudes due to topography and rapid night‐time warming. On the altitude gradient, the SOS was more sensitive to daytime temperature in areas below 800 and 2,000–4,000 m. ST_night‐time exceeded ST_daytime at other altitudes owing to night‐time warming relief of the severe restrictions on phenological processes and the reduction in frost risk. To reach a comprehensive characterization of the interaction between vegetation and climate systems, the current study suggests more investigation on the response of SOS to diurnal temperature on large scales.

Ozone Anomalies in the Free Troposphere During the COVID‐19 Pandemic

AbstractUsing the CAM‐chem Model, we simulate the response of chemical species in the free troposphere to scenarios of primary pollutant emission reductions during the COVID‐19 pandemic. Zonally averaged ozone in the free troposphere during Northern Hemisphere spring and summer is found to be 5%–15% lower than 19‐yr climatological values, in good agreement with observations. About one third of this anomaly is attributed to the reduction scenario of air traffic during the pandemic, another third to the reduction scenario of surface emissions, the remainder to 2020 meteorological conditions, including the exceptional springtime Arctic stratospheric ozone depletion. For the combined emission reductions, the overall COVID‐19 reduction in northern hemisphere tropospheric ozone in June is less than 5 ppb below 400 hPa, but reaches 8 ppb at 250 hPa. In the Southern Hemisphere, COVID‐19 related ozone reductions by 4%–6% were masked by comparable ozone increases due to other changes in 2020.

The climate impact of COVID-19-induced contrail changes

Abstract. The COVID-19 pandemic caused significant economic disruption in 2020 and severely impacted air traffic. We use a state-of-the-art Earth system model and ensembles of tightly constrained simulations to evaluate the effect of the reductions in aviation traffic on contrail radiative forcing and climate in 2020. In the absence of any COVID-19-pandemic-caused reductions, the model simulates a contrail effective radiative forcing (ERF) of 62 ± 59 mW m−2 (2 standard deviations). The contrail ERF has complex spatial and seasonal patterns that combine the offsetting effect of shortwave (solar) cooling and longwave (infrared) heating from contrails and contrail cirrus. Cooling is larger in June–August due to the preponderance of aviation in the Northern Hemisphere, while warming occurs throughout the year. The spatial and seasonal forcing variations also map onto surface temperature variations. The net land surface temperature change due to contrails in a normal year is estimated at 0.13 ± 0.04 K (2 standard deviations), with some regions warming as much as 0.7 K. The effect of COVID-19 reductions in flight traffic decreased contrails. The unique timing of such reductions, which were maximum in Northern Hemisphere spring and summer when the largest contrail cooling occurs, means that cooling due to fewer contrails in boreal spring and fall was offset by warming due to fewer contrails in boreal summer to give no significant annual averaged ERF from contrail changes in 2020. Despite no net significant global ERF, because of the spatial and seasonal timing of contrail ERF, some land regions would have cooled slightly (minimum −0.2 K) but significantly from contrail changes in 2020. The implications for future climate impacts of contrails are discussed.

Record low ozone values over the Arctic in boreal spring 2020

Abstract. Ozone data derived from the Tropospheric Monitoring Instrument (TROPOMI) sensor on board the Sentinel-5 Precursor satellite show exceptionally low total ozone columns in the polar region of the Northern Hemisphere (Arctic) in spring 2020. Minimum total ozone column values around or below 220 Dobson units (DU) were seen over the Arctic for 5 weeks in March and early April 2020. Usually the persistence of such low total ozone column values in spring is only observed in the polar Southern Hemisphere (Antarctic) and not over the Arctic. These record low total ozone columns were caused by a particularly strong polar vortex in the stratosphere with a persistent cold stratosphere at higher latitudes, a prerequisite for ozone depletion through heterogeneous chemistry. Based on the ERA5, which is the fifth generation of the European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric reanalysis, the Northern Hemisphere winter 2019/2020 (from December to March) showed minimum polar cap temperatures consistently below 195 K around 20 km altitude, which enabled enhanced formation of polar stratospheric clouds. The special situation in spring 2020 is compared and discussed in context with two other Northern Hemisphere spring seasons, namely those in 1997 and 2011, which also displayed relatively low total ozone column values. However, during these years, total ozone columns below 220 DU over several consecutive days were not observed in spring. The similarities and differences of the atmospheric conditions of these three events and possible explanations for the observed features are presented and discussed. It becomes apparent that the monthly mean of the minimum total ozone column value for March 2020 (221 DU) was clearly below the respective values found in March 1997 (267 DU) and 2011 (252 DU), which highlights the special evolution of the polar stratospheric ozone layer in the Northern Hemisphere in spring 2020. A comparison with a typical ozone hole over the Antarctic (e.g., in 2016) indicates that although the Arctic spring 2020 situation is remarkable, with total ozone column values around or below 220 DU observed over a considerable area (up to 0.9 million km2), the Antarctic ozone hole shows total ozone columns typically below 150 DU over a much larger area (of the order of 20 million km2). Furthermore, total ozone columns below 220 DU are typically observed over the Antarctic for about 4 months.

Statistical and Solar Cycle Distribution of Daily Flux $\ge 10^{9}\mbox{ cm}^{-2}$ d−1 sr−1 for $E>2$ MeV Electrons Observed by GOES During 1987 – 2019

We studied the statistical and solar cycle distribution of daily flux $\ge 10^{9}\mbox{ cm}^{-2}$ d−1 sr−1 for $E>2$ MeV electrons Observed by GOES from 1987 to 2019. There were 282 days with daily flux $\ge 10^{9}\mbox{ cm}^{-2}$ d−1 sr−1 for $E>2$ MeV electrons during this period. Of the 282 days, 71.63% of them have the daily flux <2.0 $\times 10^{9}\mbox{ cm}^{-1}$ d−1sr−1, 19.86% of them with the daily flux fall in the interval ≥2.0 $\times 10^{9}\mbox{ cm}^{-2}$ d−1 sr−1 and <3.0 $\times 10^{9}\mbox{ cm}^{-2}$ d−1 sr−1, 4.26% of them have the daily flux in the interval between ≥3.0 $\times 10^{9}\mbox{ cm}^{-2}$ d−1 sr−1 and <4.0 $\times 10^{9}\mbox{ cm}^{-2}$ d−1 sr−1, and 4.26% of them have the daily flux ≥4.0 $\times 10^{9}\mbox{ cm}^{-2}$ d−1 sr−1. The daily flux $\ge 10^{9}\mbox{ cm}^{-2}$ d−1 sr−1 for $E>2$ MeV electrons that lasted for 1, 2, 3, 4, 5, 6, 7 and 10 days accounted for 18.44%, 17.02%, 20.21%, 15.6%, 8.87%, 6.38%, 9.93% and 3.55%, respectively. Among all the daily fluxes $\ge 10^{9}\mbox{ cm}^{-2}$ d−1 sr−1, 47.79% of them occurred in the northern hemisphere spring, 36.03% of them occurred in the fall, and 16.18% of them occurred in the other months. More than 82% of the daily flux $\ge 10^{9}\mbox{ cm}^{-2}$ d−1 sr−1 for $E>2$ MeV electrons appeared in the descending phase for each solar cycle. The greater percentage of the electrons of daily flux $\ge 10^{9}\mbox{ cm}^{-2}$ d−1 sr−1 for $E>2$ MeV occurred during the descending phase for the solar cycle with higher amplitude. Also, for the solar cycle with higher amplitude, the lower the percentage of the electrons of daily flux $\ge 10^{9}\mbox{ cm}^{-2}$ d−1 sr−1 of $E>2$ MeV occurred in the period from two years before to three years after the solar cycle peak.

Characteristic features of water ice clouds over Olympus and Arsia Mons using MOM and MRO observations

The present study used the observations from Mars Color Camera (MCC) onboard Mars Orbiter Mission, from the two instruments onboard Mars Reconnaissance Orbiter, i.e., Mars Climate Sounder (MCS) and Mars Color Imager (MARCI), for investigating the water ice cloud appearance over two Martian volcanos, Olympus Mons and Arsia Mons. Indeed, these regions offer an opportunity to explore the dynamical effects related to the orographic clouds and give an idea about their interactions with atmospheric transport. Also, the long-term MCS profile observations are much useful to emphasize the sub-seasonal, seasonal, and interannual variability of clouds at different altitudes. The MCC and MARCI images show a cloud patch over Olympus Mons within the aphelion and a thin cloud trails over Arsia Mons within the perihelion of Mars years. Night-time MCS observations suggest an appearance of thick low altitude clouds within 15–32 ​km height during LS ​= ​35–150° and thin high-altitude clouds within 30–50 ​km height during LS ​= ​225–315°. The profile observations over both the volcanic regions show that the atmospheric temperature variations more strongly control the water ice cloud distribution at lower altitudes during northern hemispheric spring and summer. In contrast, the high altitude thin clouds during southern hemispheric spring and summer are found to be more associated with the elevated dustiness and vertical advection of dust-laden mountain induced regional circulation, as suggested by MarsWRF simulated wind. The appearance of the consistent thick followed by thin clouds during aphelion and perihelion season shows a nearly constant cloud water content of ~0.2 and ~0.05 pr μm. The high or low magnitude of cloud water content could be distinguished from the peak water ice extinction within the column, as observed in the inter-annual variations. However, irrespective of low cloud water content during the second half of the year, the presence of high altitude thin clouds leads to an overall cloud vertical depth (≥30 ​km) higher (mostly visible during the night) than the first half of the year. Comparison of the nighttime appearance of thick clouds (centered at ~20 ​km) during the first half and thin clouds (centered at ~40 ​km) during the second half of the year over two volcanos indicates the suitable atmospheric conditions in the case of the Olympus Mons for the former type clouds and over Arsia Mons for the later. Also, the appearance of thick clouds mostly resembles the consistent and stable aphelion cloud cycle. In contrast, the thin high altitude clouds are more variable and influenced by the vertical advection during the perihelion season. Besides, these high altitude clouds drive the more prominent east-west asymmetry in the cloud abundance over the Arsia Mons region during the perihelion period.

Arts and crafts as an educational strategy and coping mechanism for Republic of Korea and United States parents during the COVID-19 pandemic.

The COVID-19 pandemic and ensuing stay-at-home orders have shifted family lives worldwide. Government regulations about social distancing and isolation have resulted in parents/carers and children spending most of their time together in private spaces. During the northern hemisphere spring 2020 semester, most childcare and school systems closed and parents had to dramatically modify their balance between work and home life. Using data from consumer reports, online parenting forums and blog posts, and Google Trends, the authors of this article explored how some parents have shifted towards cultural and creative enrichment as a resource to occupy their children during governmental stay-at-home directives in both the United States and the Republic of Korea. The authors found that arts and crafts and educational toy sales have increased, parents are sharing advice and resources for at-home creative activities, and arts and cultural institutions have expanded their free online content. Finally, this article discusses whether the short-term stressors from COVID-19 might lead to long-term changes in parenting and sustained interest in these resources. The authors’ findings provide additional support for the importance of arts and humanities in the educational experience of children.

Modeled Climate Responses to Realistic Extremes of Northern Hemisphere Spring and Summer Snow Anomalies

AbstractNorthern Hemisphere (NH) snow cover extent (SCE) has diminished in spring and early summer since the 1960s. Historical simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5) estimated about half as much NH SCE reduction as observed, and thus underestimated the associated climate responses. This study investigates atmospheric responses to realistic decreasing snow anomalies using multiple ensemble transient integrations of climate models forced by observed light and heavy NH snow cover years, specifically satellite-based observations of NH SCE and snow water equivalent from March to August in 1990 (light snow) and 1985 (heavy snow), as a proxy for the trend. The primary atmospheric responses to March–August NH snow reduction are decreased soil moisture, increased surface air temperature, general tropospheric warming in the extratropics and the Arctic, increased geopotential heights, and weakening of the midlatitude jet stream and eddy kinetic energy. The localized response is maintained by persistent increased diabatic heating due to reduced snow anomalies and resulting soil moisture drying, and the remote atmospheric response results partly from horizontal propagation of stationary Rossby wave energy and also from a transient eddy feedback mechanism. In summer, atmospheric responses are significant in both the Arctic and the tropics and are mostly induced by contemporaneous snow forcing, but also by the summer soil moisture dry anomaly associated with early snow melting.

The effect of interactive ozone chemistry on weak and strong stratospheric polar vortex events

Abstract. Modeling and observational studies have reported effects of stratospheric ozone extremes on Northern Hemisphere spring climate. Recent work has further suggested that the coupling of ozone chemistry and dynamics amplifies the surface response to midwinter sudden stratospheric warmings (SSWs). Here we study the importance of interactive ozone chemistry in representing the stratospheric polar vortex and Northern Hemisphere winter surface climate variability. We contrast two simulations from the interactive and specified chemistry (and thus ozone) versions of the Whole Atmosphere Community Climate Model, which is designed to isolate the impact of interactive ozone on polar vortex variability. In particular, we analyze the response with and without interactive chemistry to midwinter SSWs, March SSWs, and strong polar vortex events (SPVs). With interactive chemistry, the stratospheric polar vortex is stronger and more SPVs occur, but we find little effect on the frequency of midwinter SSWs. At the surface, interactive chemistry results in a pattern resembling a more negative North Atlantic Oscillation following midwinter SSWs but with little impact on the surface signatures of late winter SSWs and SPVs. These results suggest that including interactive ozone chemistry is important for representing North Atlantic and European winter climate variability.

Assessment of spatio-temporal distribution of CO2 over greater Asia using the WRF–CO2 model

In-depth knowledge of global and regional carbon budget is required for effective policymaking to mitigate the global climate change. However, Asian carbon budget shows large uncertainty due to both lack of sufficient observations and detailed understanding of the existing CO2 observations. A regional air quality model (WRF–CO2) is set up for simulating atmospheric CO2 variations over the greater Asia region (68–124°E, 2°S–45°N) for the period 2010–2012. The WRF–CO2 simulations are compared with observations from nine sites and a global Atmospheric Chemistry Transport Model (ACTM). The comparisons suggest WRF–CO2 simulation is able to capture large scale features in the observed variabilities, with varied ability at fine scales depending on representation of surface fluxes and meteorology around the observation sites. Analysis of CO2 signals from individual flux components suggests that ocean flux has least contribution to the CO2 variation ( 80%). CO2 mixing ratios are found to be maximum in northern hemisphere (NH) winter over East Asia, while they are maximum in NH spring over Indian subcontinent. Observed peak-to-trough seasonal amplitude is lowest (4.5 ppm) for the site Bukit Koto Tabang, Indonesia and highest (29.5 ppm) for Shangdianzi in China. Statistical analysis from monthly mean CO2 time series shows that correlation coefficient and normalised standard deviation with observations, are generally equal or better for the WRF–CO2 than the coarser resolution ACTM. Study of synoptic scale CO2 variations shows that the WRF–CO2 is able to better resolve daytime signatures than those in the night. Year-to-year CO2 variations of seasonal cycle amplitude is highest (~5 ppm) at Nainital, India compared to all other sites.

MARCI-observed clouds in the Hellas Basin during northern hemisphere summer on Mars: Interpretation with the NASA/Ames Legacy Mars Global Climate Model

We present a study that is motivated by a population of water ice clouds in the Hellas Basin that has been observed by the MARs Color Imager (MARCI) instrument on the Mars Reconnaissance Orbiter (MRO) to persist throughout the majority of Northern Hemisphere (NH) summer. Although water ice clouds are present in Hellas at very low opacities throughout NH spring, they noticeably thicken after Ls 60° and continue to do so until their peak optical thickness is attained at Ls ~120°. They dissipate rapidly from Ls 120° to 150°, and by Ls 150°, the only clouds in Hellas are on the southern side of the basin and are indistinguishable from the polar hood clouds. We use the NASA/Ames Legacy Mars Global Climate Model (GCM), which is supported by the Agency's Mars Climate Modeling Center, to investigate the dynamical and microphysical mechanisms that control the formation and evolution of Hellas water ice clouds. We show that water is transported from the North Polar Residual Cap (NPRC) southward across the equator and into the Hellas region. Water vapor is confined down low by cloud formation in the aphelion cloud belt, thus limiting the effectiveness of transport by the zonal mean overturning circulation (i.e., the Hadley cell). Thus, contrary to the commonly held conceptual understanding that the Hadley cell controls cross-equatorial water transport during this season, we show that the southward transport of water is done primarily in the vapor phase by stationary eddies at nearly all latitudes, including across the equator. Clouds form near the surface in the basin as moist air mixes with cold polar air on the western side of Hellas and are subsequently transported clockwise around the north side of the basin by the low-level cyclonic circulation. The simulated Hellas clouds have small particle sizes (~3–5 μm), are very low, and exist as long as the NPRC is exposed.

Heterogeneous spring phenology shifts affected by climate: supportive evidence from two remotely sensed vegetation indices

The Northern Hemisphere spring greenup (SG) has advanced between 0–12 days per decade since early 1980s as inferred from multiple satellite time series. The wide range of SG shifts is mainly due to the fact that these studies cover different periods and regions, and using different satellite records. Assessing the spatial heterogeneity of SG trends associated with different satellites is essential for robustly interpreting phenological dynamics and their responses to climate. We investigated the heterogeneity of the SG trends and their responses to climate variability with two satellite products (1) Terra Moderate Resolution Imaging Spectroradiometer (MODIS) and (2) Advanced Very High Resolution Radiometer (AVHRR) over the period 2001–2013. Both MODIS and AVHRR agreed in showing the spatial distribution of mean SG, and SG advancement in northern Canada, the eastern United States, and Russia, and SG delay in western North America, parts of Baltic Europe, and East Asia. However, we identified contrasting MODIS and AVHRR SG trends in the northern high latitudes. Our analyses of correlations between SG and preseason climate drivers indicated that temperature dominated the interannual variability of SG. Preseason, the period preceding SG and highly correlated with the timing of SG has experienced much stronger warming than the spring season. MODIS and AVHRR indicated consistent temperature sensitivity of SG across biomes, even though the MODIS inferred SG is better correlated and more sensitive to temperature across biomes as compared to AVHRR. The sensitivities of SG to temperature across biomes is stable but with a slight increase over 2001–2013, in comparison with that over 1988–2000. The increased SG-temperature sensitivity is associated with increased precipitation during the spring season, which regulated the sensitivity of SG to spring temperature.

Origin of Solar Rotational Periodicity and Harmonics Identified in the Interplanetary Magnetic Field B_{z} Component Near the Earth During Solar Cycles 23 and 24

Periodic variations in solar-wind and geomagnetic parameters have long been recognized. In this work, we examine the periodic properties in the interplanetary magnetic field (IMF) near the Earth using satellite observations from 1996 to 2017. We pay particular attention to short-term periodicities (solar rotational period and its harmonics) of IMF B_{z} by distinguishing between the geocentric solar ecliptic (GSE) and the geocentric solar magnetospheric (GSM) coordinates. We find that, for nearly all of the years in Solar Cycles 23 and 24, IMF B_{z} exhibits periodic changes with a period of the solar rotation or its harmonics or both. We emphasize that these changes are far more pronounced in the GSM coordinates than in the GSE coordinates and during the northern hemisphere spring and fall seasons than the other two seasons. We attribute this result to an exquisite harmony between the Russell–McPherron effect and a well-defined IMF polarity that shows either a two- or four-sector structure for a long period of time.

The importance of interactive chemistry for stratosphere–troposphere coupling

Abstract. Recent observational and modeling studies suggest that stratospheric ozone depletion not only influences the surface climate in the Southern Hemisphere (SH), but also impacts Northern Hemisphere (NH) spring, which implies a strong interaction between dynamics and chemistry. Here, we systematically analyze the importance of interactive chemistry with respect to the representation of stratosphere–troposphere coupling and in particular the effects on NH surface climate during the recent past. We use the interactive and specified chemistry version of NCAR's Whole Atmosphere Community Climate Model coupled to an ocean model to investigate differences in the mean state of the NH stratosphere as well as in stratospheric extreme events, namely sudden stratospheric warmings (SSWs), and their surface impacts. To be able to focus on differences that arise from two-way interactions between chemistry and dynamics in the model, the specified chemistry model version uses a time-evolving, model-consistent ozone field generated by the interactive chemistry model version. We also test the effects of zonally symmetric versus asymmetric prescribed ozone, evaluating the importance of ozone waves in the representation of stratospheric mean state and variability. The interactive chemistry simulation is characterized by a significantly stronger and colder polar night jet (PNJ) during spring when ozone depletion becomes important. We identify a negative feedback between lower stratospheric ozone and atmospheric dynamics during the breakdown of the stratospheric polar vortex in the NH, which contributes to the different characteristics of the PNJ between the simulations. Not only the mean state, but also stratospheric variability is better represented in the interactive chemistry simulation, which shows a more realistic distribution of SSWs as well as a more persistent surface impact afterwards compared with the simulation where the feedback between chemistry and dynamics is switched off. We hypothesize that this is also related to the feedback between ozone and dynamics via the intrusion of ozone-rich air into polar latitudes during SSWs. The results from the zonally asymmetric ozone simulation are closer to the interactive chemistry simulations, implying that under a model-consistent ozone forcing, a three-dimensional (3-D) representation of the prescribed ozone field is desirable. This suggests that a 3-D ozone forcing, as recommended for the upcoming CMIP6 simulations, has the potential to improve the representation of stratospheric dynamics and chemistry. Our findings underline the importance of the representation of interactive chemistry and its feedback on the stratospheric mean state and variability not only in the SH but also in the NH during the recent past.

The effects on student retention by implementing contextualised, program-specific learning modules in an online student success course

This practice report examines the results of inserting program-specific, contextualised modules and instructors into an online student success course in a two-year college environment. The results of multiple semesters of pre-contextualised instruction (Northern Hemisphere Spring and Fall 2015) and post-contextualisation instruction (Northern Hemisphere Fall 2016 and Spring 2017), showed an increase in next semester retention. Additionally, ten student success course instructors were interviewed to determine critical elements of the course. Instructors revealed that time management, stress management, and program-specific assignments were the most beneficial components of the course.