Assessment of Recent Changes in Dust over South Asia Using RegCM4 Regional Climate Model

Pre-monsoon dust aerosols over Indian regions are closely linked to the monsoon dynamics and Indian summer monsoon rainfall. Past observational studies have shown a decline in dust loading over the Indian landmass potentially caused by changing rainfall patterns over the desert regions. Such changes are expected to have a far-reaching impact on regional energy balance and monsoon rainfall. Using a regional climate-chemistry model, RegCM4.5, with an updated land module, we have simulated the long-term (2001–2015) changes in dust over the arid and semi-arid dust source regions of the North-Western part of the subcontinent. It is found that the area-averaged dust aerosol optical depth (AOD) over the arid and semi-arid desert regions has declined by 17% since the start of this millennium. The rainfall over these regions exhibits a positive trend of 0.1 mm day−1year−1 and a net increase of >50%. The wet deposition is found to be dominant and ~five-fold larger in magnitude over dry deposition and exhibits total changes of ~79 and 48% in the trends in atmospheric dust. As a response, a significant difference in the surface (11%), top of the atmosphere radiative forcing (7%), and widespread atmospheric cooling are observed in the short wave domain of radiation spectrum over the Northern part of the Indian landmass. Such quantification and long-term change studies are necessary for understanding regional climate change and the water cycle

The Arctic Temperature Response to Global and Regional Anthropogenic Sulfate Aerosols

The mechanisms behind Arctic warming and associated climate changes are difficult todiscern. Also, the complex local processes and feedbacks like aerosol-cloud-climateinteractions are yet to be quantified. Here, using the Community Earth System Model(CAM5) experiments, with emission enhancement of anthropogenic sulfate 1) five-foldglobally, 2) ten-times over Asia, and 3) ten-times over Europe we show that regionalemissions of sulfate aerosols alter seasonal warming over the Arctic, i.e., colder summerand warmer winter. European emissions play a dominant role in cooling during the summerseason (0.7 K), while Asian emissions dominate the warming during the winter season(maximum ∼0.6 K) in the Arctic surface. The cooling/warming is associated with a negative/positive cloud radiative forcing. During the summer season increase in low–mid levelclouds, induced by sulfate emissions, favours the solar dimming effect that reduces thedownwelling radiation to the surface and thus leads to surface cooling. Warmer winters areassociated with enhanced high-level clouds that induce a positive radiative forcing at thetop of the atmosphere. This study points to the importance of international strategies beingimplemented to control sulfate emissions to combat air pollution. Such strategies will alsoaffect the Arctic cooling/warming associated with a cloud radiative forcing caused bysulfate emission change

Observation of Cloud Base Height and Precipitation Characteristics at a Polar Site Ny-Ålesund, Svalbard Using Ground-Based Remote Sensing and Model Reanalysis

Clouds play a significant role in regulating the Arctic climate and water cycle due to their impacts on radiative balance through various complex feedback processes. However, there are still large discrepancies in satellite and numerical model-derived cloud datasets over the Arctic region due to a lack of observations. Here, we report observations of cloud base height (CBH) characteristics measured using a Vaisala CL51 ceilometer at Ny-Ålesund, Svalbard. The study highlights the monthly and seasonal CBH characteristics at the location. It is found that almost 40% of the lowest CBHs fall within a height range of 0.5–1 km. The second and third cloud bases that could be detected by the ceilometer are mostly concentrated below 3 km during summer but possess more vertical spread during the winter season. Thin and low-level clouds appear to be dominant during the summer. Low-level clouds are found to be dominant and observed in 76% of cases. The mid and high-level clouds occur in ~16% and ~7% of cases, respectively. Further, micro rain radar (MRR2) observed enhanced precipitation and snowfall events during the winter and spring which are found to be associated with the lowest CBHs within 2 km from the ground. The frontal process associated with synoptic-scale meteorological conditions explains the variabilities in CBH and precipitation at the observation site when compared for two contrasting winter precipitation events. The findings of the study could be useful for model evaluation of cloud precipitation relationships and satellite data validation in the Arctic environment

Storage, degradation, and new connectivity of face-related semantic memory in Alzheimer's disease

Background: Excepting amnesia, impairment of other domains also hampers the activity of daily living in Alzheimer's disease (AD). Although prosopagnosia poses problem in interacting with other persons, it rarely causes problem during interaction with close relatives as known voice acts as cue for recognition. Objective: In a cohort of AD, we planned to study errors in recognition, naming, and assigning relationship of close relatives, to assess the type and frequency of errors and to explain with current knowledge and hypothesis. Materials and Methods: This cross-sectional study was conducted in Memory Clinic of Medical College Hospital, Kolkata, India, between July 2013 and June 2015. Patients were evaluated by history, general neurological examination, and neuropsychological tests. A structured questionnaire was used to assess recognition (use of honorifics) and naming defect of close relatives. Results: AD was diagnosed in 42 patients. Prosopagnosia was found in 14 and anomia in 6 patients. Four patients exhibited problem during conversation with close relatives. They assigned name and relation of one generation earlier to close relatives with proper recognitions. Discussion: We got predictive error of name and relation assignment of close relatives by one generation back with normal recognition. It can be explained by two memory traces in connection of face-visual and name (with/without relation) representation, earlier being hierarchically older and more resistant to wearing. Conclusions: We hypothesize that the name/relation store is orderly conserved. In AD, after degradation of part of name/relation store, a new wiring might be built up between these two traces

Tropospheric warming over the northern Indian Ocean caused by South Asian anthropogenic aerosols: possible impact on the upper troposphere and lower stratosphere

Atmospheric concentrations of South Asian anthropogenic aerosols and their transport play a key role in the regional hydrological cycle. Here, we use the ECHAM6-HAMMOZ chemistry–climate model to show the structure and implications of the transport pathways of these aerosols during spring (March–May). Our simulations indicate that large amounts of anthropogenic aerosols are transported from South Asia to the northern Indian Ocean and western Pacific. These aerosols are then lifted into the upper troposphere and lower stratosphere (UTLS) by the ascending branch of the Hadley circulation, where they enter the westerly jet. They are further transported to the Southern Hemisphere (∼15–30∘ S) and downward (320–340 K) via westerly ducts over the tropical Atlantic (5∘ S–5∘ N, 10–40∘ W) and Pacific (5∘ S–5∘ N, 95–140∘ E). The carbonaceous aerosols are also transported to the Arctic, leading to local heating (0.08–0.3 K per month, an increase by 10 %–60 %).The presence of anthropogenic aerosols causes a negative radiative forcing (RF) at the top of the atmosphere (TOA) (−0.90 ± 0.089 W m−2) and surface (−5.87 ± 0.31 W m−2) and atmospheric warming (+4.96 ± 0.24 W m−2) over South Asia (60–90∘ E, 8–23∘ N), except over the Indo-Gangetic Plain (75–83∘ E, 23–30∘ N), where RF at the TOA is positive (+1.27 ± 0.16 W m−2) due to large concentrations of absorbing aerosols. The carbonaceous aerosols lead to in-atmospheric heating along the aerosol column extending from the boundary layer to the upper troposphere (0.1 to 0.4 K per month, increase by 4 %–60 %) and in the lower stratosphere at 40–90∘ N (0.02 to 0.3 K per month, increase by 10 %–60 %). The increase in tropospheric heating due to aerosols results in an increase in water vapor concentrations, which are then transported from the northern Indian Ocean–western Pacific to the UTLS over 45–45∘ N (increasing water vapor by 1 %–10 %)