This work discusses using a series of regional relaxation or ‘nudging’ experiments on hindcasts, whereby certain dynamical fields are relaxed back to reanalysis in order to investigate their role on the growth of errors and biases in key components of the Asian Summer Monsoon. The methodology is well motivated and the application of this methodology for studying these errors in coupled NWP and seasonal hindcasts in the Met Office Global Coupled models is new. The results highlight a number of key processes through which errors arise.

This work sheds light on the source of errors and biases in the Met Office Global Coupled models which is important for future model development (that this work will undoubtedly support). This paper fits well within the scope of the journal. The comments I provide for improving the manuscript are about clarity and presentation. Thus I would recommend this article be published after the following comments are addressed.

Specific Comments

Introduction

1. This section provides good motivatation for the relaxation methodology but not the wider context of why the specific configurations used in the paper were chosen. It would be of great benefit to the reader to introduce the components of the ASM variability and describing some of the mechanisms through which biases can arise in models as a result of these not being faithfully represented. Specifically it would be useful for the authors to describe the role of each of the regions used in the nudging experiments in controlling the ASM.
2. There are also many acronyms and areas introduced later on in the paper, some were not defined. For clarity, it would be useful for these to be introduced earlier: the WNPSH, EASMI, the EIO, EEIO and the WEIO.
3. Line 44, pg 2, states ‘also to increase sample size’. Is sample size referring to deterministic versus ensemble?

Data description and methods

1. In the results section there is discussion of a control run, please clarify what this is.
2. Could the authors clarify why the hindcast ensembles are compared to reanalysis, GPCP and OISSTv2 but the Coupled NWP forecasts are compared against FOAM and MetUM operational analysis?

3.1 ASM errors in seasonal hindcasts

1. Fig.2 is this the control run?
2. Pg 6, Line 139. It seems a bit strange to comment on the results of the Indonesia and Philippines nudging experiments without showing these. However, if they make a significant contribution to the errors produced by the MC region then it is not necessary for the authors to do so, this seems to be the case but it would be good for the authors to clarify this. This also motivates the authors' assumption that errors in this region are mostly linear. 

3.2 Emergence of Indian Ocean SST errors in coupled NWP hindcasts

1. Line 284, pg 15 why was 1 ensemble initialised each day, were they different ensemble members, if so, why? Can the authors clarify what the forecast validity time is? Why were forecasts initialised everyday of 2020 if only certain forecast validity periods between 30 June - 31st August were used?
2. Line 289, pg 15. Does EEIO stand for Eastern Eq. Indian Ocean and WEIO western eq. Indian Ocean and do they correspond to box 1 and 2 in Fig 13. If so please specify.
3. There seems to be a rapid change/increase in errors in precipitation, wind, heat flux and SST after day 9. Did atmospheric conditions change on this day perhaps? I.e. If there was low precipitation then there is low variability in the precipitation and hence there would be smaller errors associated with it.  
4. Figure 12b, 14b there is no dashed red line representing mld in the nudged MC experiment.

3.3 Development of ocean errors in the Equatorial Indian Ocean

1. Line 380, pg 21 is the ‘day-1 start day’ the 9th of each month? Is this why that date is used in Fig 15, 16 and 17.
2. Line 385, pg 21 ‘easter EIO’, I assume this is meant to say eastern EIO but is this defined already as EEIO (i.e. box 1 in Fig 13)?

This manuscript is a noteworthy continuation and expansion of the work initiated by Martin et al. (2021), delving deeper into the development of errors in the Asian Summer Monsoon (ASM) through regional relaxation experiments in initialized hindcasts. The study's utilization of nudging techniques within ensemble experiments in both coupled NWP and GloSea5 hindcasts provides valuable insights into the role of the Maritime Continent and the Equatorial Indian Ocean in ASM circulation errors. These findings not only corroborate previous hypotheses but also contribute novel insights into the error dynamics of the ASM, marking a significant advancement in climate modeling for this region.

The manuscript is well-structured and demonstrates thorough research, making it a valuable contribution to the field. Overall, the paper stands out for its methodological rigor and the practical implications of its findings in improving climate models. I recommend the acceptance of this manuscript for publication.