## 1 Introduction
### Atmospheric Temperature Trend (MSUI/AMSU)  
In order to estimate multidecadal changes in global atmospheric temperature, measurements from two different measuring systems, balloon-borne radiosondes and satellite-borne microwave-sounding equipment, have been largely used [17; 18; 19; 20; 21]. The Microwave Sounding Unit (MSU) and Advanced Microwave Sounding Unit (AMSU) were flown on a series of polar-orbiting weather satellites launched by NOAA in 1978 and 1998, respectively. The microwave measurements are constructed by merging measurements from both and are referred to as the MSU dataset. These satellite-based instruments provide measurements processed by different organizations and agencies to produce valuable data products that contribute to our understanding of climate dynamics, weather forecasting, and the detection of long-term temperature trends. The satellite microwave sounding observations of the lower troposphere and middle troposphere since 1979 show a rise in global temperature of 0.156 \({}^{\circ}\)K/decade and 0.091 \({}^{\circ}\)K/decade, respectively [22; 23].  
By incorporating the observed prevalence of vertically extended atmospheric brown clouds over the Indian Ocean and Asia into general circulation model (GCM) simulations [24], it is suggested that these clouds contribute significantly to regional lower atmospheric warming trends. The study proposed that the observed retreat of Himalayan glaciers could be attributed to the combined warming trend of 0.25 \({}^{\circ}\)K/decade associated with atmospheric brown clouds and greenhouse gas emissions. The findings indicate that the observed trend of warming in the mid-troposphere across west-central Asia in recent years has significant implications for the amplified variability of western disturbances and an elevated likelihood of intense winter precipitation events in the western Himalaya region [25]. However, the precise implications of this climate warming signal on the hydrological cycle of the HKH region are yet to be understood.  
The long-term temperature trends in two cities, Delhi and Kolkata, in the Indo-Gangetic plains based on radiosonde data from 1973 to 2008 reveal that both cities experienced warming trends in the lower troposphere until 400 hPa, with the maximum increase occurring at 700 hPa [26]. A notable shift from cooling to warming trends occurred between 1958-1985 and 1973-2008. The study suggests that increased emissions from fossil fuels, urbanization, and aerosol distribution, including greenhouse gases and particulate matter, may have influenced these temperature trends, but further comprehensive observations are needed to establish their specific roles. Using radiosonde data, researchers in India have managed to examine the variability of annual and seasonal tropospheric temperature changes from 1971 to 2015 [27]. It was reported that the all-India mean annual temperature has experienced significant increasing trends at surface, 700 hPa, and 500 hPa levels, driven primarily by pronounced winter warming. Surface air temperatures in India have shown significant increases across all seasons. North and South India exhibit varying temperature trends, with surface and 700 hPa levels showing significant increases, influenced by differences in aerosol concentrations between the two regions. The layer average temperature was growing in the lower troposphere (surface-850 hPa) and falling in the lower stratosphere (100-50 hPa) in a trend study of 10 years of Aqua-AIRS sounding atmospheric temperature data over a few major Indian cities [28]. The decreasing trend in the lower stratosphere was found to be prominent. A literature review of the lower and middle tropospheric temperature trend studies in the HKH region using MSU datasets is tabulated below (Table 1).