The warming of the atmosphere related to the absorption of aerosols has an influence on snow cover, which thereby reduces the effect of reflectance after deposition. The warming produces an atmospheric dynamical feedback, termed an “elevated-heat-pump (EHP) effect”, which increases moisture, cloud cover, and deep convection over northern India, as well as enhancing the rate of snow melt in the Himalayas and on the Tibetan Plateau (TP). Observations and models were analyzed to explore the impact of these processes on the spring-time climate.

Observational evidence is firstly presented, illustrating that the Indo-Gangetic Plain (IGP) region, which is bounded by the high-altitude Himalayan mountains, is subject to heavy loading of absorbing aerosols, i.e., black carbon and dust. This leads to widespread enhancement warming over the Tibetan Plateau and accelerated snowmelt on the western Tibetan Plateau (WTP) and the Himalayas. In terms of the aerosol loading over the IGP, the two pre-monsoon seasons of 2004 and 2005 were strikingly contrasting. In 2004, the warming of the TP was widespread relative to 2005. It covered most of the WTP and the Himalayas and was closely linked to the patterns of snow melt. Consistent with the Elevated Heat Pump hypothesis, we find that an increased loading of absorbing aerosols over the IGP in the pre-monsoon season is associated with an increased heating of the upper troposphere, which enhances the rate of snowmelt over the Himalayas and the WTP in April-May.

Secondly, a coupled atmosphere-ocean global climate model (CSIRO-Mk3.6) is used to investigate the role of aerosol forcing agents as drivers of snow melting trends in the TP region. Our results suggest that the heating trend of the atmosphere by aerosols can lead to widespread enhanced warming over the TP and to snow melt in the western TP and Himalayas. An aerosol layer, composed mainly of dust transported from adjacent deserts and black carbon from local emissions, builds up in the Boreal Spring over the Indo-Gangetic Plain against the foothills of the Himalayas and the TP. This layer, which extends from the surface to a high elevation, heats the mid-troposphere by absorbing solar radiation. The heating then produces an acceleration of the rate of snow melt in the Himalayas and on the TP.

Part 1. Satellite observations of enhanced pre-monsoon aerosol loading and tropospheric warming over Tibetan Plateau

1. INTRODUCTION

2. Data and Methodology

3. Results

3.1 Aerosol Optical Depth over IGP

3.2. Enhanced warming over the TP

3.3 Accelerated snow melting over the TP

4. Discussion

Part 2. Study of aerosol Effect on accelerated snow melting over the Tibetan Plateau using CMIP5 simulation data

1. Introduction

2. Data and Methodology

2.1 observation data

2.2 Model description

3. Results

3.1. Model evaluation

3.2. Aerosols effects on snow melt

4. Summary and discussion